# Inter-Integrated Circuit (I2C)

[中文]

## Introduction

I2C is a serial, synchronous, multi-device, half-duplex communication protocol that allows co-existence of multiple masters and slaves on the same bus. I2C uses two bidirectional open-drain lines: serial data line (SDA) and serial clock line (SCL), pulled up by resistors.

ESP32-P4 has 2 I2C controller(s) (also called port), responsible for handling communication on the I2C bus.

A single I2C controller can be a master or a slave.

Additionally, the ESP32-P4 chip has 1 low-power (LP) I2C controller. It is the cut-down version of regular I2C. Usually, the LP I2C controller only support basic I2C functionality with a much smaller RAM size, and does not support slave mode. For a full list of difference between HP I2C and LP I2C, please refer to the ESP32-P4 Technical Reference Manual > I2C Controller (I2C) > Features [PDF].

You can use LP I2C peripheral when HP I2C is not sufficient for users' usage. But please note again the LP I2C does not support all HP I2C functions. Please read documentation before you use it.

Typically, an I2C slave device has a 7-bit address or 10-bit address. ESP32-P4 supports both I2C Standard-mode (Sm) and Fast-mode (Fm) which can go up to 100 kHz and 400 kHz respectively.

Warning

The clock frequency of SCL in master mode should not be larger than 400 kHz.

Note

The frequency of SCL is influenced by both the pull-up resistor and the wire capacitance. Therefore, it is strongly recommended to choose appropriate pull-up resistors to make the frequency accurate. The recommended value for pull-up resistors usually ranges from 1 kΩ to 10 kΩ.

Keep in mind that the higher the frequency, the smaller the pull-up resistor should be (but not less than 1 kΩ). Indeed, large resistors will decline the current, which will increase the clock switching time and reduce the frequency. A range of 2 kΩ to 5 kΩ is recommended, but adjustments may also be necessary depending on their current draw requirements.

Note

We realized that our first version of the I2C slave driver had some problems and was not easy to use, so we have prepared a second version of the I2C slave driver, which solves many of the problems with our current I2C slave and which will be the focus of our maintenance. We encourage and recommend that you use the second version of the I2C slave driver, which you can do by enabling CONFIG_I2C_ENABLE_SLAVE_DRIVER_VERSION_2. This document focuses on the content of I2C slave v2.0. If you still want to read programming guide of I2C slave v1.0, please refer to I2C Slave v1.0. The I2C slave v1.0 driver will be removed with the IDF v6.0 update.

## I2C Clock Configuration

- `i2c_clock_source_t::I2C_CLK_SRC_DEFAULT`: Default I2C source clock.

- `i2c_clock_source_t::I2C_CLK_SRC_XTAL`: External crystal for I2C clock source.

- `i2c_clock_source_t::I2C_CLK_SRC_RC_FAST`: Internal 20 MHz RC oscillator for I2C clock source.

## I2C File Structure

I2C file structure

Public headers that need to be included in the I2C application

- `i2c.h`: The header file of legacy I2C APIs (for apps using legacy driver).

- `i2c_master.h`: The header file that provides standard communication mode specific APIs (for apps using new driver with master mode).

- `i2c_slave.h`: The header file that provides standard communication mode specific APIs (for apps using new driver with slave mode).

Note

The legacy driver can't coexist with the new driver. Include `i2c.h` to use the legacy driver or the other two headers to use the new driver. Please keep in mind that the legacy driver is now deprecated and will be removed in future.

Public headers that have been included in the headers above

- `i2c_types_legacy.h`: The legacy public types that are only used in the legacy driver.

- `i2c_types.h`: The header file that provides public types.

## Functional Overview

The I2C driver offers following services:

- Resource Allocation - covers how to allocate I2C bus with properly set of configurations. It also covers how to recycle the resources when they finished working.

- I2C Master Controller - covers behavior of I2C master controller. Introduce data transmit, data receive, and data transmit and receive.

- I2C Slave Controller - covers behavior of I2C slave controller. Involve data transmit and data receive.

- Power Management - describes how different source clock will affect power consumption.

- IRAM Safe - describes tips on how to make the I2C interrupt work better along with a disabled cache.

- Thread Safety - lists which APIs are guaranteed to be thread safe by the driver.

- Kconfig Options - lists the supported Kconfig options that can bring different effects to the driver.

### Resource Allocation

The I2C master bus is represented by `i2c_master_bus_handle_t` in the driver. The available ports are managed in a resource pool that allocates a free port on request.

#### Install I2C master bus and device

The I2C master bus is designed based on bus-device model. So `i2c_master_bus_config_t` and `i2c_device_config_t` are required separately to allocate the I2C master bus instance and I2C device instance.

I2C master bus-device module

I2C master bus requires the configuration that specified by `i2c_master_bus_config_t`:

- `i2c_master_bus_config_t::i2c_port` sets the I2C port used by the controller.

- `i2c_master_bus_config_t::sda_io_num` sets the GPIO number for the serial data bus (SDA).

- `i2c_master_bus_config_t::scl_io_num` sets the GPIO number for the serial clock bus (SCL).

- `i2c_master_bus_config_t::clk_source` selects the source clock for I2C bus. The available clocks are listed in `i2c_clock_source_t`. For the effect on power consumption of different clock source, please refer to Power Management section.

- `i2c_master_bus_config_t::glitch_ignore_cnt` sets the glitch period of master bus, if the glitch period on the line is less than this value, it can be filtered out, typically value is 7.

- `i2c_master_bus_config_t::intr_priority` sets the priority of the interrupt. If set to `0` , then the driver will use a interrupt with low or medium priority (priority level may be one of 1, 2 or 3), otherwise use the priority indicated by `i2c_master_bus_config_t::intr_priority`. Please use the number form (1, 2, 3) , not the bitmask form ((1<<1), (1<<2), (1<<3)).

- `i2c_master_bus_config_t::trans_queue_depth` sets the depth of internal transfer queue. Only valid in asynchronous transaction.

- `i2c_master_bus_config_t::enable_internal_pullup` enables internal pullups. Note: This is not strong enough to pullup buses under high-speed frequency. A suitable external pullup is recommended.

- `i2c_master_bus_config_t::allow_pd` configures if the driver allows the system to power down the peripheral in light sleep mode. Before entering sleep, the system will backup the I2C register context, which will be restored later when the system exit the sleep mode. Powering down the peripheral can save more power, but at the cost of more memory consumed to save the register context. It's a tradeoff between power consumption and memory consumption. This configuration option relies on specific hardware feature, if you enable it on an unsupported chip, you will see error message like `not able to power down in light sleep`.

If the configurations in `i2c_master_bus_config_t` is specified, then `i2c_new_master_bus()` can be called to allocate and initialize an I2C master bus. This function will return an I2C bus handle if it runs correctly. Specifically, when there are no more I2C port available, this function will return `ESP_ERR_NOT_FOUND` error.

I2C master device requires the configuration that specified by `i2c_device_config_t`:

- `i2c_device_config_t::dev_addr_length` configure the address bit length of the slave device. It can be chosen from enumerator `I2C_ADDR_BIT_LEN_7` or `I2C_ADDR_BIT_LEN_10` (if supported).

- `i2c_device_config_t::device_address` sets the I2C device raw address. Please parse the device address to this member directly. For example, the device address is 0x28, then parse 0x28 to `i2c_device_config_t::device_address`, don't carry a write or read bit.

- `i2c_device_config_t::scl_speed_hz` sets the SCL line frequency of this device.

- `i2c_device_config_t::scl_wait_us` sets the SCL await time (in μs). Usually this value should not be very small because slave stretch will happen in pretty long time (It's possible even stretch for 12 ms). Set `0` means use default register value.

Once the `i2c_device_config_t` structure is populated with mandatory parameters, `i2c_master_bus_add_device()` can be called to allocate an I2C device instance and mounted to the master bus then. This function will return an I2C device handle if it runs correctly. Specifically, when the I2C bus is not initialized properly, calling this function will result in a `ESP_ERR_INVALID_ARG` error.

    #include "driver/i2c_master.h"

    i2c_master_bus_config_t i2c_mst_config = {
        .clk_source = I2C_CLK_SRC_DEFAULT,
        .i2c_port = TEST_I2C_PORT,
        .scl_io_num = I2C_MASTER_SCL_IO,
        .sda_io_num = I2C_MASTER_SDA_IO,
        .glitch_ignore_cnt = 7,
        .flags.enable_internal_pullup = true,
    };

    i2c_master_bus_handle_t bus_handle;
    ESP_ERROR_CHECK(i2c_new_master_bus(&i2c_mst_config, &bus_handle));

    i2c_device_config_t dev_cfg = {
        .dev_addr_length = I2C_ADDR_BIT_LEN_7,
        .device_address = 0x58,
        .scl_speed_hz = 100000,
    };

    i2c_master_dev_handle_t dev_handle;
    ESP_ERROR_CHECK(i2c_master_bus_add_device(bus_handle, &dev_cfg, &dev_handle));

#### Get I2C master handle via port

When the I2C master handle has been initialized in one module (e.g. the audio module), but it is not convenient to acquire this handle in another module (e.g. the video module). You can use the helper function, `i2c_master_get_bus_handle()` to retrieve the initialized handle via port. Ensure that the handle has already been initialized beforehand to avoid potential errors.

    // Source File 1
    #include "driver/i2c_master.h"
    i2c_master_bus_handle_t bus_handle;
    i2c_master_bus_config_t i2c_mst_config = {
        ... // same as others
    };
    ESP_ERROR_CHECK(i2c_new_master_bus(&i2c_mst_config, &bus_handle));

    // Source File 2
    #include "driver/i2c_master.h"
    i2c_master_bus_handle_t handle;
    ESP_ERROR_CHECK(i2c_master_get_bus_handle(0, &handle));

#### Install I2C master bus with LP I2C Peripheral

Install I2C master bus with LP I2C peripheral is almost as same as how HP I2C peripheral is installed. However, there are still some difference should be taken focus on, including IOs, clock sources, I2C port number, etc. Following code will show how to install I2C master bus with LP_I2C.

    #include "driver/i2c_master.h"

    i2c_master_bus_config_t i2c_mst_config = {
        .clk_source = LP_I2C_SCLK_DEFAULT,    // clock source for LP I2C, might different from HP I2C
        .i2c_port = LP_I2C_NUM_0,             // Assign to LP I2C port
        .scl_io_num = 7,                      // SCL IO number. Please refer to technical reference manual
        .sda_io_num = 6,                      // SDA IO number. Please refer to technical reference manual
        .glitch_ignore_cnt = 7,
        .flags.enable_internal_pullup = true,
    };

    i2c_master_bus_handle_t bus_handle;
    ESP_ERROR_CHECK(i2c_new_master_bus(&i2c_mst_config, &bus_handle));

    i2c_device_config_t dev_cfg = {
        .dev_addr_length = I2C_ADDR_BIT_LEN_7,
        .device_address = 0x58,
        .scl_speed_hz = 100000,
    };

    i2c_master_dev_handle_t dev_handle;
    ESP_ERROR_CHECK(i2c_master_bus_add_device(bus_handle, &dev_cfg, &dev_handle));

#### Uninstall I2C master bus and device

If a previously installed I2C bus or device is no longer needed, it's recommended to recycle the resource by calling `i2c_master_bus_rm_device()` or `i2c_del_master_bus()`, so as to release the underlying hardware.

#### Install I2C slave device

I2C slave requires the configuration specified by `i2c_slave_config_t`:

- `i2c_slave_config_t::i2c_port` sets the I2C port used by the controller.

- `i2c_slave_config_t::sda_io_num` sets the GPIO number for serial data bus (SDA).

- `i2c_slave_config_t::scl_io_num` sets the GPIO number for serial clock bus (SCL).

- `i2c_slave_config_t::clk_source` selects the source clock for I2C bus. The available clocks are listed in `i2c_clock_source_t`. For the effect on power consumption of different clock source, please refer to Power Management section.

- `i2c_slave_config_t::send_buf_depth` sets the sending software buffer length.

- `i2c_slave_config_t::receive_buf_depth` sets the receiving software buffer length.

- `i2c_slave_config_t::intr_priority` sets the priority of the interrupt. If set to `0` , then the driver will use a interrupt with low or medium priority (priority level may be one of 1, 2 or 3), otherwise use the priority indicated by `i2c_slave_config_t::intr_priority`. Please use the number form (1, 2, 3), instead of the bitmask form ((1<<1), (1<<2), (1<<3)). Please pay attention that once the interrupt priority is set, it cannot be changed until `i2c_del_slave_device()` is called.

- `i2c_slave_config_t::addr_bit_len` Set this variable to `I2C_ADDR_BIT_LEN_10` if the slave should have a 10-bit address.

- `i2c_slave_config_t::allow_pd` If set, the driver will backup/restore the I2C registers before/after entering/exist sleep mode. By this approach, the system can power off I2C's power domain. This can save power, but at the expense of more RAM being consumed.

- `i2c_slave_config_t::broadcast_en` Set this to true to enable the slave broadcast. When the slave receives the general call address 0x00 from the master and the R/W bit followed is 0, it responds to the master regardless of its own address.

- `i2c_slave_config_t::enable_internal_pullup` Set this to enable internal pull-up. Even though, an output pull-up resistance is strongly recommended.

Once the `i2c_slave_config_t` structure is populated with mandatory parameters, `i2c_new_slave_device()` can be called to allocate and initialize an I2C master bus. This function will return an I2C bus handle if it runs correctly. Specifically, when there are no more I2C port available, this function will return `ESP_ERR_NOT_FOUND` error.

    i2c_slave_config_t i2c_slv_config = {
        .i2c_port = I2C_SLAVE_NUM,
        .clk_source = I2C_CLK_SRC_DEFAULT,
        .scl_io_num = I2C_SLAVE_SCL_IO,
        .sda_io_num = I2C_SLAVE_SDA_IO,
        .slave_addr = ESP_SLAVE_ADDR,
        .send_buf_depth = 100,
        .receive_buf_depth = 100,
    };

    i2c_slave_dev_handle_t slave_handle;
    ESP_ERROR_CHECK(i2c_new_slave_device(&i2c_slv_config, &slave_handle));

#### Uninstall I2C slave device

If a previously installed I2C bus is no longer needed, it's recommended to recycle the resource by calling `i2c_del_slave_device()`, so that to release the underlying hardware.

### I2C Master Controller

After installing the I2C master driver by `i2c_new_master_bus()`, ESP32-P4 is ready to communicate with other I2C devices. I2C APIs allow the standard transactions. Like the wave as follows:

#### I2C Master Write

After installing I2C master bus successfully, you can simply call `i2c_master_transmit()` to write data to the slave device. The principle of this function can be explained by following chart.

In order to organize the process, the driver uses a command link, that should be populated with a sequence of commands and then passed to I2C controller for execution.

I2C master write to slave

Simple example for writing data to slave:

    #define DATA_LENGTH 100
    i2c_master_bus_config_t i2c_mst_config = {
        .clk_source = I2C_CLK_SRC_DEFAULT,
        .i2c_port = I2C_PORT_NUM_0,
        .scl_io_num = I2C_MASTER_SCL_IO,
        .sda_io_num = I2C_MASTER_SDA_IO,
        .glitch_ignore_cnt = 7,
    };
    i2c_master_bus_handle_t bus_handle;

    ESP_ERROR_CHECK(i2c_new_master_bus(&i2c_mst_config, &bus_handle));

    i2c_device_config_t dev_cfg = {
        .dev_addr_length = I2C_ADDR_BIT_LEN_7,
        .device_address = 0x58,
        .scl_speed_hz = 100000,
    };

    i2c_master_dev_handle_t dev_handle;
    ESP_ERROR_CHECK(i2c_master_bus_add_device(bus_handle, &dev_cfg, &dev_handle));

    ESP_ERROR_CHECK(i2c_master_transmit(dev_handle, data_wr, DATA_LENGTH, -1));

I2C master write also supports transmit multi-buffer in one transaction. Take following transaction as a simple example:

    uint8_t control_phase_byte = 0;
    size_t control_phase_size = 0;
    if (/*condition*/) {
        control_phase_byte = 1;
        control_phase_size = 1;
    }

    uint8_t *cmd_buffer = NULL;
    size_t cmd_buffer_size = 0;
    if (/*condition*/) {
        uint8_t cmds[4] = {BYTESHIFT(lcd_cmd, 3), BYTESHIFT(lcd_cmd, 2), BYTESHIFT(lcd_cmd, 1), BYTESHIFT(lcd_cmd, 0)};
        cmd_buffer = cmds;
        cmd_buffer_size = 4;
    }

    uint8_t *lcd_buffer = NULL;
    size_t lcd_buffer_size = 0;
    if (buffer) {
        lcd_buffer = (uint8_t*)buffer;
        lcd_buffer_size = buffer_size;
    }

    i2c_master_transmit_multi_buffer_info_t lcd_i2c_buffer[3] = {
        {.write_buffer = &control_phase_byte, .buffer_size = control_phase_size},
        {.write_buffer = cmd_buffer, .buffer_size = cmd_buffer_size},
        {.write_buffer = lcd_buffer, .buffer_size = lcd_buffer_size},
    };

    i2c_master_multi_buffer_transmit(handle, lcd_i2c_buffer, sizeof(lcd_i2c_buffer) / sizeof(i2c_master_transmit_multi_buffer_info_t), -1);

#### I2C Master Read

After installing I2C master bus successfully, you can simply call `i2c_master_receive()` to read data from the slave device. The principle of this function can be explained by following chart.

I2C master read from slave

Simple example for reading data from slave:

    #define DATA_LENGTH 100
    i2c_master_bus_config_t i2c_mst_config = {
        .clk_source = I2C_CLK_SRC_DEFAULT,
        .i2c_port = I2C_PORT_NUM_0,
        .scl_io_num = I2C_MASTER_SCL_IO,
        .sda_io_num = I2C_MASTER_SDA_IO,
        .glitch_ignore_cnt = 7,
    };
    i2c_master_bus_handle_t bus_handle;

    ESP_ERROR_CHECK(i2c_new_master_bus(&i2c_mst_config, &bus_handle));

    i2c_device_config_t dev_cfg = {
        .dev_addr_length = I2C_ADDR_BIT_LEN_7,
        .device_address = 0x58,
        .scl_speed_hz = 100000,
    };

    i2c_master_dev_handle_t dev_handle;
    ESP_ERROR_CHECK(i2c_master_bus_add_device(bus_handle, &dev_cfg, &dev_handle));

    i2c_master_receive(dev_handle, data_rd, DATA_LENGTH, -1);

#### I2C Master Write and Read

Some I2C device needs write configurations before reading data from it. Therefore, an interface called `i2c_master_transmit_receive()` can help. The principle of this function can be explained by following chart.

I2C master write to slave and read from slave

Please note that no STOP condition bit is inserted between the write and read operations; therefore, this function is suited to read a register from an I2C device. A simple example for writing and reading from a slave device:

    i2c_device_config_t dev_cfg = {
        .dev_addr_length = I2C_ADDR_BIT_LEN_7,
        .device_address = 0x58,
        .scl_speed_hz = 100000,
    };

    i2c_master_dev_handle_t dev_handle;
    ESP_ERROR_CHECK(i2c_master_bus_add_device(bus_handle, &dev_cfg, &dev_handle));
    uint8_t buf[20] = {0x20};
    uint8_t buffer[2];
    ESP_ERROR_CHECK(i2c_master_transmit_receive(dev_handle, buf, sizeof(buf), buffer, 2, -1));

#### I2C Master Probe

I2C driver can use `i2c_master_probe()` to detect whether the specific device has been connected on I2C bus. If this function return `ESP_OK`, that means the device has been detected.

Important

Pull-ups must be connected to the SCL and SDA pins when this function is called. If you get ESP_ERR_TIMEOUT while xfer_timeout_ms was parsed correctly, you should check the pull-up resistors. If you do not have proper resistors nearby, setting flags.enable_internal_pullup as true is also acceptable.

I2C master probe

Simple example for probing an I2C device:

    i2c_master_bus_config_t i2c_mst_config_1 = {
        .clk_source = I2C_CLK_SRC_DEFAULT,
        .i2c_port = TEST_I2C_PORT,
        .scl_io_num = I2C_MASTER_SCL_IO,
        .sda_io_num = I2C_MASTER_SDA_IO,
        .glitch_ignore_cnt = 7,
        .flags.enable_internal_pullup = true,
    };
    i2c_master_bus_handle_t bus_handle;

    ESP_ERROR_CHECK(i2c_new_master_bus(&i2c_mst_config_1, &bus_handle));
    ESP_ERROR_CHECK(i2c_master_probe(bus_handle, 0x22, -1));
    ESP_ERROR_CHECK(i2c_del_master_bus(bus_handle));

#### I2C Master Execute Customized Transactions

Not all I2C devices strictly adhere to the standard I2C protocol, as different manufacturers may implement custom variations. For example, some devices require the address to be shifted, while others do not. Similarly, certain devices mandate acknowledgment (ACK) checks for specific operations, whereas others might not. To accommodate these variations, `i2c_master_execute_defined_operations()` function allow developers to define and execute fully customized I2C transactions. This flexibility ensures seamless communication with non-standard devices by tailoring the transaction sequence, addressing, and acknowledgment behavior to the device's specific requirements.

Note

If you want to define your address in `i2c_operation_job_t`, please set `i2c_device_config_t::device_address` as I2C_DEVICE_ADDRESS_NOT_USED to skip internal address configuration in driver.

For address configuration of using defined transactions, given that a device address is 0x20, there are two situations, see following example:

    i2c_device_config_t i2c_device = {
        .device_address = I2C_DEVICE_ADDRESS_NOT_USED,
        .scl_speed_hz = 100 * 1000,
        .scl_wait_us = 20000,
    };

    i2c_master_dev_handle_t dev_handle;

    i2c_master_bus_add_device(bus_handle, &i2c_device, &dev_handle);

    // Situation one: The device does not allow device address shift
    uint8_t address1 = 0x20;
    i2c_operation_job_t i2c_ops1[] = {
        { .command = I2C_MASTER_CMD_START },
        { .command = I2C_MASTER_CMD_WRITE, .write = { .ack_check = false, .data = (uint8_t *) &address1, .total_bytes = 1 } },
        { .command = I2C_MASTER_CMD_STOP },
    };

    // Situation one: The device should left shift one byte with carrying a write or read bit (official protocol)
    uint8_t address2 = (0x20 << 1 | 0); // (0x20 << 1 | 1)
    i2c_operation_job_t i2c_ops2[] = {
        { .command = I2C_MASTER_CMD_START },
        { .command = I2C_MASTER_CMD_WRITE, .write = { .ack_check = false, .data = (uint8_t *) &address2, .total_bytes = 1 } },
        { .command = I2C_MASTER_CMD_STOP },
    };

There are also some devices does not need an address, you can directly do transaction with data:

    uint8_t data[8] = {0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88};

    i2c_operation_job_t i2c_ops[] = {
        { .command = I2C_MASTER_CMD_START },
        { .command = I2C_MASTER_CMD_WRITE, .write = { .ack_check = false, .data = (uint8_t *)data, .total_bytes = 8 } },
        { .command = I2C_MASTER_CMD_STOP },
    };

    i2c_master_execute_defined_operations(dev_handle, i2c_ops, sizeof(i2c_ops) / sizeof(i2c_operation_job_t), -1);

As for read direction, the theory is same but please always be aware the last byte of read before stop should always be nack. Example is as follows:

    uint8_t address = (0x20 << 1 | 1);
    uint8_t rcv_data[10] = {};

    i2c_operation_job_t i2c_ops[] = {
        { .command = I2C_MASTER_CMD_START },
        { .command = I2C_MASTER_CMD_WRITE, .write = { .ack_check = false, .data = (uint8_t *) &address, .total_bytes = 1 } },
        { .command = I2C_MASTER_CMD_READ, .read = { .ack_value = I2C_ACK_VAL, .data = (uint8_t *)rcv_data, .total_bytes = 9 } },
        { .command = I2C_MASTER_CMD_READ, .read = { .ack_value = I2C_NACK_VAL, .data = (uint8_t *)(rcv_data + 9), .total_bytes = 1 } }, // This must be nack.
        { .command = I2C_MASTER_CMD_STOP },
    };

    i2c_master_execute_defined_operations(dev_handle, i2c_ops, sizeof(i2c_ops) / sizeof(i2c_operation_job_t), -1);

### I2C Slave Controller

After installing the I2C slave driver by `i2c_new_slave_device()`, ESP32-P4 is ready to communicate with other I2C masters as a slave.

The I2C slave is not as subjective as the I2C master which knows when it should send data and when it should receive data. The I2C slave is very passive in most cases, that means the I2C slave's ability to send and receive data is largely dependent on the master's actions. Therefore, we throw two callback functions in the driver that represent read requests and write requests from the I2C master.

#### I2C Slave Write

You can get I2C slave write event be register `i2c_slave_event_callbacks_t::on_request` callback, and in a task when get the request event, you can call i2c_slave_write to send data.

Simple example for transmitting data:

    // Prepare a callback function
    static bool i2c_slave_request_cb(i2c_slave_dev_handle_t i2c_slave, const i2c_slave_request_event_data_t *evt_data, void *arg)
    {
        i2c_slave_event_t evt = I2C_SLAVE_EVT_TX;
        BaseType_t xTaskWoken = 0;
        xQueueSendFromISR(context->event_queue, &evt, &xTaskWoken);
        return xTaskWoken;
    }

    // Register callback in a task
    i2c_slave_event_callbacks_t cbs = {
        .on_request = i2c_slave_request_cb,
    };
    ESP_ERROR_CHECK(i2c_slave_register_event_callbacks(context.handle, &cbs, &context));

    // Waiting for request event and send data in a task
    static void i2c_slave_task(void *arg)
    {
        uint8_t buffer_size = 64;
        uint32_t write_len;
        uint8_t *data_buffer;

        while (true) {
            i2c_slave_event_t evt;
            if (xQueueReceive(context->event_queue, &evt, 10) == pdTRUE) {
                ESP_ERROR_CHECK(i2c_slave_write(handle, data_buffer, buffer_size, &write_len, 1000));
            }
        }
        vTaskDelete(NULL);
    }

#### I2C Slave Read

Same as write, you can get I2C slave read event be register `i2c_slave_event_callbacks_t::on_receive` callback, and in a task when get the request event, you can save the data and do what you want.

Simple example for receiving data:

    // Prepare a callback function
    static bool i2c_slave_receive_cb(i2c_slave_dev_handle_t i2c_slave, const i2c_slave_rx_done_event_data_t *evt_data, void *arg)
    {
        i2c_slave_event_t evt = I2C_SLAVE_EVT_RX;
        BaseType_t xTaskWoken = 0;
        // You can get data and length via i2c_slave_rx_done_event_data_t
        xQueueSendFromISR(context->event_queue, &evt, &xTaskWoken);
        return xTaskWoken;
    }

    // Register callback in a task
    i2c_slave_event_callbacks_t cbs = {
        .on_receive = i2c_slave_receive_cb,
    };
    ESP_ERROR_CHECK(i2c_slave_register_event_callbacks(context.handle, &cbs, &context));

### Register Event Callbacks

#### I2C master callbacks

When an I2C master bus triggers an interrupt, a specific event will be generated and notify the CPU. If you have some functions that need to be called when those events occurred, you can hook your functions to the ISR (Interrupt Service Routine) by calling `i2c_master_register_event_callbacks()`. Since the registered callback functions are called in the interrupt context, users should ensure the callback function doesn't attempt to block (e.g. by making sure that only FreeRTOS APIs with `ISR` suffix are called from the function). The callback functions are required to return a boolean value, to tell the ISR whether a high priority task is woken up by it.

I2C master event callbacks are listed in the `i2c_master_event_callbacks_t`.

Although I2C is a synchronous communication protocol, asynchronous behavior is supported by registering above callbacks. In this way, I2C APIs will be non-blocking interface. But note that on the same bus, only one device can adopt asynchronous operation.

Important

I2C master asynchronous transaction is still an experimental feature (The issue is that when asynchronous transaction is very large, it will cause memory problem).

- `i2c_master_event_callbacks_t::on_recv_done` sets a callback function for master "transaction-done" event. The function prototype is declared in `i2c_master_callback_t`.

#### I2C slave callbacks

When an I2C slave bus triggers an interrupt, a specific event will be generated and notify the CPU. If you have some function that needs to be called when those events occurred, you can hook your function to the ISR (Interrupt Service Routine) by calling `i2c_slave_register_event_callbacks()`. Since the registered callback functions are called in the interrupt context, users should ensure the callback function doesn't attempt to block (e.g. by making sure that only FreeRTOS APIs with `ISR` suffix are called from the function). The callback function has a boolean return value, to tell the caller whether a high priority task is woken up by it.

I2C slave event callbacks are listed in the `i2c_slave_event_callbacks_t`.

- `i2c_slave_event_callbacks_t::on_request` sets a callback function for request event.

- `i2c_slave_event_callbacks_t::on_receive` sets a callback function for receive event. The function prototype is declared in `i2c_slave_received_callback_t`.

### Power Management

If the controller clock source is selected to `I2C_CLK_SRC_XTAL`, then the driver won't install power management lock for it, which is more suitable for a low power application as long as the source clock can still provide sufficient resolution.

### IRAM Safe

By default, the I2C interrupt will be deferred when the cache is disabled for reasons like writing or erasing flash. Thus the event callback functions will not get executed in time, which is not expected in a real-time application.

There's a Kconfig option CONFIG_I2C_ISR_IRAM_SAFE that will:

1. Enable the interrupt being serviced even when cache is disabled.

2. Place all functions that used by the ISR into IRAM.

3. Place driver object into DRAM (in case it's mapped to PSRAM by accident).

This will allow the interrupt to run while the cache is disabled but will come at the cost of increased IRAM consumption.

### Thread Safety

The factory function `i2c_new_master_bus()` and `i2c_new_slave_device()` are guaranteed to be thread safe by the driver, which means that the functions can be called from different RTOS tasks without protection by extra locks.

I2C master operation functions are also guaranteed to be thread safe by bus operation semaphore.

- `i2c_master_transmit()`

- `i2c_master_multi_buffer_transmit()`

- `i2c_master_transmit_receive()`

- `i2c_master_receive()`

- `i2c_master_probe()`

I2C slave operation functions are also guaranteed to be thread safe by bus operation semaphore.

- `i2c_slave_write()`

Other functions are not guaranteed to be thread-safe. Thus, you should avoid calling them in different tasks without mutex protection.

### Kconfig Options

- CONFIG_I2C_ISR_IRAM_SAFE controls whether the default ISR handler can work when cache is disabled, see also IRAM Safe for more information.

- CONFIG_I2C_ENABLE_DEBUG_LOG is used to enable the debug log at the cost of increased firmware binary size.

- CONFIG_I2C_ENABLE_SLAVE_DRIVER_VERSION_2 is used to enable the I2C slave driver v2.0.

## Application Examples

- peripherals/i2c/i2c_eeprom demonstrates how to use the I2C master mode to read and write data from a connected EEPROM.

- peripherals/i2c/i2c_tools demonstrates how to use the I2C Tools for developing I2C related applications, providing command-line tools for configuring the I2C bus, scanning for devices, reading and setting registers, and examining registers.

- peripherals/i2c/i2c_slave_network_sensor demonstrates how to use the I2C slave for developing I2C related applications, providing how I2C slave can behave as a network sensor, and use event callbacks to receive and send data.

## API Reference

### Header File

- components/esp_driver_i2c/include/driver/i2c_master.h

- This header file can be included with:

  >     #include "driver/i2c_master.h"

- This header file is a part of the API provided by the `esp_driver_i2c` component. To declare that your component depends on `esp_driver_i2c`, add the following to your CMakeLists.txt:

  >     REQUIRES esp_driver_i2c

  > or

  >     PRIV_REQUIRES esp_driver_i2c

### Functions

esp_err_t i2c_new_master_bus(const i2c_master_bus_config_t *bus_config, i2c_master_bus_handle_t *ret_bus_handle)

  Allocate an I2C master bus.

  Parameters:

    - bus_config -- [in] I2C master bus configuration.

    - ret_bus_handle -- [out] I2C bus handle

  Returns:

    - ESP_OK: I2C master bus initialized successfully.

    - ESP_ERR_INVALID_ARG: I2C bus initialization failed because of invalid argument.

    - ESP_ERR_NO_MEM: Create I2C bus failed because of out of memory.

    - ESP_ERR_NOT_FOUND: No more free bus.

esp_err_t i2c_master_bus_add_device(i2c_master_bus_handle_t bus_handle, const i2c_device_config_t *dev_config, i2c_master_dev_handle_t *ret_handle)

  Add I2C master BUS device.

  Parameters:

    - bus_handle -- [in] I2C bus handle.

    - dev_config -- [in] device config.

    - ret_handle -- [out] device handle.

  Returns:

    - ESP_OK: Create I2C master device successfully.

    - ESP_ERR_INVALID_ARG: I2C bus initialization failed because of invalid argument.

    - ESP_ERR_NO_MEM: Create I2C bus failed because of out of memory.

esp_err_t i2c_del_master_bus(i2c_master_bus_handle_t bus_handle)

  Deinitialize the I2C master bus and delete the handle.

  Parameters:

    bus_handle -- [in] I2C bus handle.

  Returns:

    - ESP_OK: Delete I2C bus success, otherwise, failed.

    - Otherwise: Some module delete failed.

esp_err_t i2c_master_bus_rm_device(i2c_master_dev_handle_t handle)

  I2C master bus delete device.

  Parameters:

    handle -- i2c device handle

  Returns:

    - ESP_OK: If device is successfully deleted.

esp_err_t i2c_master_transmit(i2c_master_dev_handle_t i2c_dev, const uint8_t *write_buffer, size_t write_size, int xfer_timeout_ms)

  Perform a write transaction on the I2C bus. The transaction will be undergoing until it finishes or it reaches the timeout provided.

  Note

  If a callback was registered with `i2c_master_register_event_callbacks`, the transaction will be asynchronous, and thus, this function will return directly, without blocking. You will get finish information from callback. Besides, data buffer should always be completely prepared when callback is registered, otherwise, the data will get corrupt.

  Parameters:

    - i2c_dev -- [in] I2C master device handle that created by `i2c_master_bus_add_device`.

    - write_buffer -- [in] Data bytes to send on the I2C bus.

    - write_size -- [in] Size, in bytes, of the write buffer.

    - xfer_timeout_ms -- [in] Wait timeout, in ms. Note: -1 means wait forever.

  Returns:

    - ESP_OK: I2C master transmit success

    - ESP_ERR_INVALID_ARG: I2C master transmit parameter invalid.

    - ESP_ERR_TIMEOUT: Operation timeout(larger than xfer_timeout_ms) because the bus is busy or hardware crash.

esp_err_t i2c_master_multi_buffer_transmit(i2c_master_dev_handle_t i2c_dev, i2c_master_transmit_multi_buffer_info_t *buffer_info_array, size_t array_size, int xfer_timeout_ms)

  Transmit multiple buffers of data over an I2C bus.

  This function transmits multiple buffers of data over an I2C bus using the specified I2C master device handle. It takes in an array of buffer information structures along with the size of the array and a transfer timeout value in milliseconds.

  Parameters:

    - i2c_dev -- I2C master device handle that created by `i2c_master_bus_add_device`.

    - buffer_info_array -- Pointer to buffer information array.

    - array_size -- size of buffer information array.

    - xfer_timeout_ms -- Wait timeout, in ms. Note: -1 means wait forever.

  Returns:

    - ESP_OK: I2C master transmit success

    - ESP_ERR_INVALID_ARG: I2C master transmit parameter invalid.

    - ESP_ERR_TIMEOUT: Operation timeout(larger than xfer_timeout_ms) because the bus is busy or hardware crash.

esp_err_t i2c_master_transmit_receive(i2c_master_dev_handle_t i2c_dev, const uint8_t *write_buffer, size_t write_size, uint8_t *read_buffer, size_t read_size, int xfer_timeout_ms)

  Perform a write-read transaction on the I2C bus. The transaction will be undergoing until it finishes or it reaches the timeout provided.

  Note

  If a callback was registered with `i2c_master_register_event_callbacks`, the transaction will be asynchronous, and thus, this function will return directly, without blocking. You will get finish information from callback. Besides, data buffer should always be completely prepared when callback is registered, otherwise, the data will get corrupt.

  Parameters:

    - i2c_dev -- [in] I2C master device handle that created by `i2c_master_bus_add_device`.

    - write_buffer -- [in] Data bytes to send on the I2C bus.

    - write_size -- [in] Size, in bytes, of the write buffer.

    - read_buffer -- [out] Data bytes received from i2c bus.

    - read_size -- [in] Size, in bytes, of the read buffer.

    - xfer_timeout_ms -- [in] Wait timeout, in ms. Note: -1 means wait forever.

  Returns:

    - ESP_OK: I2C master transmit-receive success

    - ESP_ERR_INVALID_ARG: I2C master transmit parameter invalid.

    - ESP_ERR_TIMEOUT: Operation timeout(larger than xfer_timeout_ms) because the bus is busy or hardware crash.

esp_err_t i2c_master_receive(i2c_master_dev_handle_t i2c_dev, uint8_t *read_buffer, size_t read_size, int xfer_timeout_ms)

  Perform a read transaction on the I2C bus. The transaction will be undergoing until it finishes or it reaches the timeout provided.

  Note

  If a callback was registered with `i2c_master_register_event_callbacks`, the transaction will be asynchronous, and thus, this function will return directly, without blocking. You will get finish information from callback. Besides, data buffer should always be completely prepared when callback is registered, otherwise, the data will get corrupt.

  Parameters:

    - i2c_dev -- [in] I2C master device handle that created by `i2c_master_bus_add_device`.

    - read_buffer -- [out] Data bytes received from i2c bus.

    - read_size -- [in] Size, in bytes, of the read buffer.

    - xfer_timeout_ms -- [in] Wait timeout, in ms. Note: -1 means wait forever.

  Returns:

    - ESP_OK: I2C master receive success

    - ESP_ERR_INVALID_ARG: I2C master receive parameter invalid.

    - ESP_ERR_TIMEOUT: Operation timeout(larger than xfer_timeout_ms) because the bus is busy or hardware crash.

esp_err_t i2c_master_probe(i2c_master_bus_handle_t bus_handle, uint16_t address, int xfer_timeout_ms)

  Probe I2C address, if address is correct and ACK is received, this function will return ESP_OK.

  Attention

    Pull-ups must be connected to the SCL and SDA pins when this function is called. If you get `ESP_ERR_TIMEOUT while`xfer_timeout_ms`was parsed correctly, you should check the pull-up resistors. If you do not have proper resistors nearby.` flags.enable_internal_pullup` is also acceptable.

  Note

  The principle of this function is to sent device address with a write command. If the device on your I2C bus, there would be an ACK signal and function returns `ESP_OK`. If the device is not on your I2C bus, there would be a NACK signal and function returns `ESP_ERR_NOT_FOUND`. `ESP_ERR_TIMEOUT` is not an expected failure, which indicated that the i2c probe not works properly, usually caused by pull-up resistors not be connected properly. Suggestion check data on SDA/SCL line to see whether there is ACK/NACK signal is on line when i2c probe function fails.

  Note

  There are lots of I2C devices all over the world, we assume that not all I2C device support the behavior like `device_address+nack/ack`. So, if the on line data is strange and no ack/nack got respond. Please check the device datasheet.

  Parameters:

    - bus_handle -- [in] I2C master device handle that created by `i2c_master_bus_add_device`.

    - address -- [in] I2C device address that you want to probe.

    - xfer_timeout_ms -- [in] Wait timeout, in ms. Note: -1 means wait forever (Not recommended in this function).

  Returns:

    - ESP_OK: I2C device probe successfully

    - ESP_ERR_NOT_FOUND: I2C probe failed, doesn't find the device with specific address you gave.

    - ESP_ERR_TIMEOUT: Operation timeout(larger than xfer_timeout_ms) because the bus is busy or hardware crash.

esp_err_t i2c_master_execute_defined_operations(i2c_master_dev_handle_t i2c_dev, i2c_operation_job_t *i2c_operation, size_t operation_list_num, int xfer_timeout_ms)

  Execute a series of pre-defined I2C operations.

  This function processes a list of I2C operations, such as start, write, read, and stop, according to the user-defined `i2c_operation_job_t` array. It performs these operations sequentially on the specified I2C master device.

  Note

  The `ack_value` field in the READ operation must be set to `I2C_NACK_VAL` if the next operation is a STOP command.

  Parameters:

    - i2c_dev -- [in] Handle to the I2C master device.

    - i2c_operation -- [in] Pointer to an array of user-defined I2C operation jobs. Each job specifies a command and associated parameters.

    - operation_list_num -- [in] The number of operations in the `i2c_operation` array.

    - xfer_timeout_ms -- [in] Timeout for the transaction, in milliseconds.

  Returns:

    - ESP_OK: Transaction completed successfully.

    - ESP_ERR_INVALID_ARG: One or more arguments are invalid.

    - ESP_ERR_TIMEOUT: Transaction timed out.

    - ESP_FAIL: Other error during transaction.

esp_err_t i2c_master_register_event_callbacks(i2c_master_dev_handle_t i2c_dev, const i2c_master_event_callbacks_t *cbs, void *user_data)

  Register I2C transaction callbacks for a master device.

  Note

  User can deregister a previously registered callback by calling this function and setting the callback member in the `cbs` structure to NULL.

  Note

  When CONFIG_I2C_ISR_IRAM_SAFE is enabled, the callback itself and functions called by it should be placed in IRAM. The variables used in the function should be in the SRAM as well. The `user_data` should also reside in SRAM.

  Note

  If the callback is used for helping asynchronous transaction. On the same bus, only one device can be used for performing asynchronous operation.

  Parameters:

    - i2c_dev -- [in] I2C master device handle that created by `i2c_master_bus_add_device`.

    - cbs -- [in] Group of callback functions

    - user_data -- [in] User data, which will be passed to callback functions directly

  Returns:

    - ESP_OK: Set I2C transaction callbacks successfully

    - ESP_ERR_INVALID_ARG: Set I2C transaction callbacks failed because of invalid argument

    - ESP_FAIL: Set I2C transaction callbacks failed because of other error

esp_err_t i2c_master_bus_reset(i2c_master_bus_handle_t bus_handle)

  Reset the I2C master bus.

  Parameters:

    bus_handle -- I2C bus handle.

  Returns:

    - ESP_OK: Reset succeed.

    - ESP_ERR_INVALID_ARG: I2C master bus handle is not initialized.

    - Otherwise: Reset failed.

esp_err_t i2c_master_bus_wait_all_done(i2c_master_bus_handle_t bus_handle, int timeout_ms)

  Wait for all pending I2C transactions done.

  Parameters:

    - bus_handle -- [in] I2C bus handle

    - timeout_ms -- [in] Wait timeout, in ms. Specially, -1 means to wait forever.

  Returns:

    - ESP_OK: Flush transactions successfully

    - ESP_ERR_INVALID_ARG: Flush transactions failed because of invalid argument

    - ESP_ERR_TIMEOUT: Flush transactions failed because of timeout

    - ESP_FAIL: Flush transactions failed because of other error

esp_err_t i2c_master_get_bus_handle(i2c_port_num_t port_num, i2c_master_bus_handle_t *ret_handle)

  Retrieves the I2C master bus handle for a specified I2C port number.

  This function retrieves the I2C master bus handle for the given I2C port number. Please make sure the handle has already been initialized, and this function would simply returns the existing handle. Note that the returned handle still can't be used concurrently

  Parameters:

    - port_num -- I2C port number for which the handle is to be retrieved.

    - ret_handle -- Pointer to a variable where the retrieved handle will be stored.

  Returns:

    - ESP_OK: Success. The handle is retrieved successfully.

    - ESP_ERR_INVALID_ARG: Invalid argument, such as invalid port number

    - ESP_ERR_INVALID_STATE: Invalid state, such as the I2C port is not initialized.

### Structures

struct i2c_master_bus_config_t

  I2C master bus specific configurations.

  Public Members

  i2c_port_num_t i2c_port

    I2C port number, `-1` for auto selecting, (not include LP I2C instance)

  gpio_num_t sda_io_num

    GPIO number of I2C SDA signal, pulled-up internally

  gpio_num_t scl_io_num

    GPIO number of I2C SCL signal, pulled-up internally

  i2c_clock_source_t clk_source

    Clock source of I2C master bus

  lp_i2c_clock_source_t lp_source_clk

    LP_UART source clock selection

  uint8_t glitch_ignore_cnt

    If the glitch period on the line is less than this value, it can be filtered out, typically value is 7 (unit: I2C module clock cycle)

  int intr_priority

    I2C interrupt priority, if set to 0, driver will select the default priority (1,2,3).

  size_t trans_queue_depth

    Depth of internal transfer queue, increase this value can support more transfers pending in the background, only valid in asynchronous transaction. (Typically max_device_num * per_transaction)

  uint32_t enable_internal_pullup

    Enable internal pullups. Note: This is not strong enough to pullup buses under high-speed frequency. Recommend proper external pull-up if possible

  uint32_t allow_pd

    If set, the driver will backup/restore the I2C registers before/after entering/exist sleep mode. By this approach, the system can power off I2C's power domain. This can save power, but at the expense of more RAM being consumed

  struct i2c_master_bus_config_t flags

    I2C master config flags

struct i2c_device_config_t

  I2C device configuration.

  Public Members

  i2c_addr_bit_len_t dev_addr_length

    Select the address length of the slave device.

  uint16_t device_address

    I2C device raw address. (The 7/10 bit address without read/write bit). Macro I2C_DEVICE_ADDRESS_NOT_USED (0xFFFF) stands for skip the address config inside driver.

  uint32_t scl_speed_hz

    I2C SCL line frequency.

  uint32_t scl_wait_us

    Timeout value. (unit: us). Please note this value should not be so small that it can handle stretch/disturbance properly. If 0 is set, that means use the default reg value

  uint32_t disable_ack_check

    Disable ACK check. If this is set false, that means ack check is enabled, the transaction will be stopped and API returns error when nack is detected.

  struct i2c_device_config_t flags

    I2C device config flags

struct i2c_operation_job_t

  Structure representing an I2C operation job.

  This structure is used to define individual I2C operations (write or read) within a sequence of I2C master transactions.

  Public Members

  i2c_master_command_t command

    I2C command indicating the type of operation (START, WRITE, READ, or STOP)

  bool ack_check

    Whether to enable ACK check during WRITE operation

  uint8_t *data

    Pointer to the data to be written

    Pointer to the buffer for storing the data read from the bus

  size_t total_bytes

    Total number of bytes to write

    Total number of bytes to read

  struct i2c_operation_job_t write

    Structure for WRITE command.

    Used when the `command` is set to `I2C_MASTER_CMD_WRITE`.

  i2c_ack_value_t ack_value

    ACK value to send after the read (ACK or NACK)

  struct i2c_operation_job_t read

    Structure for READ command.

    Used when the `command` is set to `I2C_MASTER_CMD_READ`.

struct i2c_master_transmit_multi_buffer_info_t

  I2C master transmit buffer information structure.

  Public Members

  const uint8_t *write_buffer

    Pointer to buffer to be written.

  size_t buffer_size

    Size of data to be written.

struct i2c_master_event_callbacks_t

  Group of I2C master callbacks, can be used to get status during transaction or doing other small things. But take care potential concurrency issues.

  Note

  The callbacks are all running under ISR context

  Note

  When CONFIG_I2C_ISR_IRAM_SAFE is enabled, the callback itself and functions called by it should be placed in IRAM. The variables used in the function should be in the SRAM as well.

  Public Members

  i2c_master_callback_t on_trans_done

    I2C master transaction finish callback

### Macros

I2C_DEVICE_ADDRESS_NOT_USED

  Skip carry address bit in driver transmit and receive

### Header File

- components/esp_driver_i2c/include/driver/i2c_slave.h

- This header file can be included with:

  >     #include "driver/i2c_slave.h"

- This header file is a part of the API provided by the `esp_driver_i2c` component. To declare that your component depends on `esp_driver_i2c`, add the following to your CMakeLists.txt:

  >     REQUIRES esp_driver_i2c

  > or

  >     PRIV_REQUIRES esp_driver_i2c

### Functions

esp_err_t i2c_slave_receive(i2c_slave_dev_handle_t i2c_slave, uint8_t *data, size_t buffer_size)

  Read bytes from I2C internal buffer. Start a job to receive I2C data.

  Note

  This function is non-blocking, it initiates a new receive job and then returns. User should check the received data from the `on_recv_done` callback that registered by `i2c_slave_register_event_callbacks()`.

  Parameters:

    - i2c_slave -- [in] I2C slave device handle that created by `i2c_new_slave_device`.

    - data -- [out] Buffer to store data from I2C fifo. Should be valid until `on_recv_done` is triggered.

    - buffer_size -- [in] Buffer size of data that provided by users.

  Returns:

    - ESP_OK: I2C slave receive success.

    - ESP_ERR_INVALID_ARG: I2C slave receive parameter invalid.

    - ESP_ERR_NOT_SUPPORTED: This function should be work in fifo mode, but I2C_SLAVE_NONFIFO mode is configured

esp_err_t i2c_slave_transmit(i2c_slave_dev_handle_t i2c_slave, const uint8_t *data, int size, int xfer_timeout_ms)

  Write bytes to internal ringbuffer of the I2C slave data. When the TX fifo empty, the ISR will fill the hardware FIFO with the internal ringbuffer's data.

  Note

  If you connect this slave device to some master device, the data transaction direction is from slave device to master device.

  Parameters:

    - i2c_slave -- [in] I2C slave device handle that created by `i2c_new_slave_device`.

    - data -- [in] Buffer to write to slave fifo, can pickup by master. Can be freed after this function returns. Equal or larger than `size`.

    - size -- [in] In bytes, of `data` buffer.

    - xfer_timeout_ms -- [in] Wait timeout, in ms. Note: -1 means wait forever.

  Returns:

    - ESP_OK: I2C slave transmit success.

    - ESP_ERR_INVALID_ARG: I2C slave transmit parameter invalid.

    - ESP_ERR_TIMEOUT: Operation timeout(larger than xfer_timeout_ms) because the device is busy or hardware crash.

    - ESP_ERR_NOT_SUPPORTED: This function should be work in fifo mode, but I2C_SLAVE_NONFIFO mode is configured

esp_err_t i2c_slave_read_ram(i2c_slave_dev_handle_t i2c_slave, uint8_t ram_address, uint8_t *data, size_t receive_size)

  Read bytes from I2C internal ram. This can be only used when `access_ram_en` in configuration structure set to true.

  Parameters:

    - i2c_slave -- [in] I2C slave device handle that created by `i2c_new_slave_device`.

    - ram_address -- [in] The offset of RAM (Cannot larger than I2C RAM memory)

    - data -- [out] Buffer to store data read from I2C ram.

    - receive_size -- [in] Received size from RAM.

  Returns:

    - ESP_OK: I2C slave transmit success.

    - ESP_ERR_INVALID_ARG: I2C slave transmit parameter invalid.

    - ESP_ERR_NOT_SUPPORTED: This function should be work in non-fifo mode, but I2C_SLAVE_FIFO mode is configured

esp_err_t i2c_slave_write_ram(i2c_slave_dev_handle_t i2c_slave, uint8_t ram_address, const uint8_t *data, size_t size)

  Write bytes to I2C internal ram. This can be only used when `access_ram_en` in configuration structure set to true.

  Parameters:

    - i2c_slave -- [in] I2C slave device handle that created by `i2c_new_slave_device`.

    - ram_address -- [in] The offset of RAM (Cannot larger than I2C RAM memory)

    - data -- [in] Buffer to fill.

    - size -- [in] Received size from RAM.

  Returns:

    - ESP_OK: I2C slave transmit success.

    - ESP_ERR_INVALID_ARG: I2C slave transmit parameter invalid.

    - ESP_ERR_INVALID_SIZE: Write size is larger than

    - ESP_ERR_NOT_SUPPORTED: This function should be work in non-fifo mode, but I2C_SLAVE_FIFO mode is configured

esp_err_t i2c_new_slave_device(const i2c_slave_config_t *slave_config, i2c_slave_dev_handle_t *ret_handle)

  Initialize an I2C slave device.

  Parameters:

    - slave_config -- [in] I2C slave device configurations

    - ret_handle -- [out] Return a generic I2C device handle

  Returns:

    - ESP_OK: I2C slave device initialized successfully

    - ESP_ERR_INVALID_ARG: I2C device initialization failed because of invalid argument.

    - ESP_ERR_NO_MEM: Create I2C device failed because of out of memory.

esp_err_t i2c_slave_register_event_callbacks(i2c_slave_dev_handle_t i2c_slave, const i2c_slave_event_callbacks_t *cbs, void *user_data)

  Set I2C slave event callbacks for I2C slave channel.

  Note

  User can deregister a previously registered callback by calling this function and setting the callback member in the `cbs` structure to NULL.

  Note

  When CONFIG_I2C_ISR_IRAM_SAFE is enabled, the callback itself and functions called by it should be placed in IRAM. The variables used in the function should be in the SRAM as well. The `user_data` should also reside in SRAM.

  Parameters:

    - i2c_slave -- [in] I2C slave device handle that created by `i2c_new_slave_device`.

    - cbs -- [in] Group of callback functions

    - user_data -- [in] User data, which will be passed to callback functions directly

  Returns:

    - ESP_OK: Set I2C transaction callbacks successfully

    - ESP_ERR_INVALID_ARG: Set I2C transaction callbacks failed because of invalid argument

    - ESP_FAIL: Set I2C transaction callbacks failed because of other error

esp_err_t i2c_del_slave_device(i2c_slave_dev_handle_t i2c_slave)

  Deinitialize the I2C slave device.

  Parameters:

    i2c_slave -- [in] I2C slave device handle that created by `i2c_new_slave_device`.

  Returns:

    - ESP_OK: Delete I2C device successfully.

    - ESP_ERR_INVALID_ARG: I2C device initialization failed because of invalid argument.

### Structures

struct i2c_slave_config_t

  I2C slave specific configurations.

  Public Members

  i2c_port_num_t i2c_port

    I2C port number, `-1` for auto selecting

  gpio_num_t sda_io_num

    SDA IO number used by I2C bus

  gpio_num_t scl_io_num

    SCL IO number used by I2C bus

  i2c_clock_source_t clk_source

    Clock source of I2C bus.

  uint32_t send_buf_depth

    Depth of internal transfer ringbuffer, increase this value can support more transfers pending in the background

  uint16_t slave_addr

    I2C slave address

  i2c_addr_bit_len_t addr_bit_len

    I2C slave address in bit length

  int intr_priority

    I2C interrupt priority, if set to 0, driver will select the default priority (1,2,3).

  uint32_t stretch_en

    Enable slave stretch

  uint32_t broadcast_en

    I2C slave enable broadcast

  uint32_t access_ram_en

    Can get access to I2C RAM directly

  uint32_t slave_unmatch_en

    Can trigger unmatch interrupt when slave address does not match what master sends

  uint32_t allow_pd

    If set, the driver will backup/restore the I2C registers before/after entering/exist sleep mode. By this approach, the system can power off I2C's power domain. This can save power, but at the expense of more RAM being consumed

  struct i2c_slave_config_t flags

    I2C slave config flags

struct i2c_slave_event_callbacks_t

  Group of I2C slave callbacks (e.g. get i2c slave stretch cause). But take care of potential concurrency issues.

  Note

  The callbacks are all running under ISR context

  Note

  When CONFIG_I2C_ISR_IRAM_SAFE is enabled, the callback itself and functions called by it should be placed in IRAM. The variables used in the function should be in the SRAM as well.

  Public Members

  i2c_slave_stretch_callback_t on_stretch_occur

    I2C slave stretched callback

  i2c_slave_received_callback_t on_recv_done

    I2C slave receive done callback

### Header File

- components/esp_driver_i2c/include/driver/i2c_types.h

- This header file can be included with:

  >     #include "driver/i2c_types.h"

- This header file is a part of the API provided by the `esp_driver_i2c` component. To declare that your component depends on `esp_driver_i2c`, add the following to your CMakeLists.txt:

  >     REQUIRES esp_driver_i2c

  > or

  >     PRIV_REQUIRES esp_driver_i2c

### Structures

struct i2c_master_event_data_t

  Data type used in I2C event callback.

  Public Members

  i2c_master_event_t event

    The I2C hardware event that I2C callback is called.

struct i2c_slave_rx_done_event_data_t

  Event structure used in I2C slave.

  Public Members

  uint8_t *buffer

    Pointer for buffer received in callback.

struct i2c_slave_stretch_event_data_t

  Stretch cause event structure used in I2C slave.

  Public Members

  i2c_slave_stretch_cause_t stretch_cause

    Stretch cause can be got in callback

struct i2c_slave_request_event_data_t

  Event structure used in I2C slave request.

### Type Definitions

typedef int i2c_port_num_t

  I2C port number.

typedef struct i2c_master_bus_t *i2c_master_bus_handle_t

  Type of I2C master bus handle.

typedef struct i2c_master_dev_t *i2c_master_dev_handle_t

  Type of I2C master bus device handle.

typedef struct i2c_slave_dev_t *i2c_slave_dev_handle_t

  Type of I2C slave device handle.

typedef bool (*i2c_master_callback_t)(i2c_master_dev_handle_t i2c_dev, const i2c_master_event_data_t *evt_data, void *arg)

  An callback for I2C transaction.

  Param i2c_dev:

    [in] Handle for I2C device.

  Param evt_data:

    [out] I2C capture event data, fed by driver

  Param arg:

    [in] User data, set in `i2c_master_register_event_callbacks()`

  Return:

    Whether a high priority task has been waken up by this function

typedef bool (*i2c_slave_received_callback_t)(i2c_slave_dev_handle_t i2c_slave, const i2c_slave_rx_done_event_data_t *evt_data, void *arg)

  Callback signature for I2C slave.

  Param i2c_slave:

    [in] Handle for I2C slave.

  Param evt_data:

    [out] I2C capture event data, fed by driver

  Param arg:

    [in] User data, set in `i2c_slave_register_event_callbacks()`

  Return:

    Whether a high priority task has been waken up by this function

typedef bool (*i2c_slave_stretch_callback_t)(i2c_slave_dev_handle_t i2c_slave, const i2c_slave_stretch_event_data_t *evt_cause, void *arg)

  Callback signature for I2C slave stretch.

  Param i2c_slave:

    [in] Handle for I2C slave.

  Param evt_cause:

    [out] I2C capture event cause, fed by driver

  Param arg:

    [in] User data, set in `i2c_slave_register_event_callbacks()`

  Return:

    Whether a high priority task has been waken up by this function

typedef bool (*i2c_slave_request_callback_t)(i2c_slave_dev_handle_t i2c_slave, const i2c_slave_request_event_data_t *evt_data, void *arg)

  Callback signature for I2C slave request event. When this callback is triggered that means master want to read data from slave while there is no data in slave fifo. So user should write data to fifo via `i2c_slave_write`

  Param i2c_slave:

    [in] Handle for I2C slave.

  Param evt_data:

    [out] I2C receive event data, fed by driver

  Param arg:

    [in] User data, set in `i2c_slave_register_event_callbacks()`

  Return:

    Whether a high priority task has been waken up by this function

### Enumerations

enum i2c_master_status_t

  Enumeration for I2C fsm status.

  Values:

  enumerator I2C_STATUS_READ

    read status for current master command

  enumerator I2C_STATUS_WRITE

    write status for current master command

  enumerator I2C_STATUS_START

    Start status for current master command

  enumerator I2C_STATUS_STOP

    stop status for current master command

  enumerator I2C_STATUS_IDLE

    idle status for current master command

  enumerator I2C_STATUS_ACK_ERROR

    ack error status for current master command

  enumerator I2C_STATUS_DONE

    I2C command done

  enumerator I2C_STATUS_TIMEOUT

    I2C bus status error, and operation timeout

enum i2c_master_event_t

  Enumeration for I2C event.

  Values:

  enumerator I2C_EVENT_ALIVE

    i2c bus in alive status.

  enumerator I2C_EVENT_DONE

    i2c bus transaction done

  enumerator I2C_EVENT_NACK

    i2c bus nack

  enumerator I2C_EVENT_TIMEOUT

    i2c bus timeout

enum i2c_master_command_t

  Enum for I2C master commands.

  These commands are used to define the I2C master operations. They correspond to hardware-level commands supported by the I2C peripheral.

  Values:

  enumerator I2C_MASTER_CMD_START

    Start or Restart condition

  enumerator I2C_MASTER_CMD_WRITE

    Write operation

  enumerator I2C_MASTER_CMD_READ

    Read operation

  enumerator I2C_MASTER_CMD_STOP

    Stop condition

enum i2c_ack_value_t

  Enum for I2C master ACK values.

  These values define the acknowledgment (ACK) behavior during read operations.

  Values:

  enumerator I2C_ACK_VAL

    Acknowledge (ACK) signal

  enumerator I2C_NACK_VAL

    Not Acknowledge (NACK) signal

### Header File

- components/hal/include/hal/i2c_types.h

- This header file can be included with:

  >     #include "hal/i2c_types.h"

### Structures

struct i2c_hal_clk_config_t

  Data structure for calculating I2C bus timing.

  Public Members

  uint16_t clkm_div

    I2C core clock divider

  uint16_t scl_low

    I2C scl low period

  uint16_t scl_high

    I2C scl high period

  uint16_t scl_wait_high

    I2C scl wait_high period

  uint16_t sda_hold

    I2C scl low period

  uint16_t sda_sample

    I2C sda sample time

  uint16_t setup

    I2C start and stop condition setup period

  uint16_t hold

    I2C start and stop condition hold period

  uint16_t tout

    I2C bus timeout period

### Type Definitions

typedef soc_periph_i2c_clk_src_t i2c_clock_source_t

  I2C group clock source.

typedef soc_periph_lp_i2c_clk_src_t lp_i2c_clock_source_t

  LP_UART source clock.

### Enumerations

enum i2c_port_t

  I2C port number, can be I2C_NUM_0 ~ (I2C_NUM_MAX-1).

  Values:

  enumerator I2C_NUM_0

    I2C port 0

  enumerator I2C_NUM_1

    I2C port 1

  enumerator LP_I2C_NUM_0
  enumerator I2C_NUM_MAX

    I2C port max

enum i2c_addr_bit_len_t

  Enumeration for I2C device address bit length.

  Values:

  enumerator I2C_ADDR_BIT_LEN_7

    i2c address bit length 7

  enumerator I2C_ADDR_BIT_LEN_10

    i2c address bit length 10

enum i2c_mode_t

  Values:

  enumerator I2C_MODE_SLAVE

    I2C slave mode

  enumerator I2C_MODE_MASTER

    I2C master mode

  enumerator I2C_MODE_MAX

enum i2c_rw_t

  Values:

  enumerator I2C_MASTER_WRITE

    I2C write data

  enumerator I2C_MASTER_READ

    I2C read data

enum i2c_trans_mode_t

  Values:

  enumerator I2C_DATA_MODE_MSB_FIRST

    I2C data msb first

  enumerator I2C_DATA_MODE_LSB_FIRST

    I2C data lsb first

  enumerator I2C_DATA_MODE_MAX

enum i2c_addr_mode_t

  Values:

  enumerator I2C_ADDR_BIT_7

    I2C 7bit address for slave mode

  enumerator I2C_ADDR_BIT_10

    I2C 10bit address for slave mode

  enumerator I2C_ADDR_BIT_MAX

enum i2c_ack_type_t

  Values:

  enumerator I2C_MASTER_ACK

    I2C ack for each byte read

  enumerator I2C_MASTER_NACK

    I2C nack for each byte read

  enumerator I2C_MASTER_LAST_NACK

    I2C nack for the last byte

  enumerator I2C_MASTER_ACK_MAX

enum i2c_slave_stretch_cause_t

  Enum for I2C slave stretch causes.

  Values:

  enumerator I2C_SLAVE_STRETCH_CAUSE_ADDRESS_MATCH

    Stretching SCL low when the slave is read by the master and the address just matched

  enumerator I2C_SLAVE_STRETCH_CAUSE_TX_EMPTY

    Stretching SCL low when TX FIFO is empty in slave mode

  enumerator I2C_SLAVE_STRETCH_CAUSE_RX_FULL

    Stretching SCL low when RX FIFO is full in slave mode

  enumerator I2C_SLAVE_STRETCH_CAUSE_SENDING_ACK

    Stretching SCL low when slave sending ACK

enum i2c_slave_read_write_status_t

  Values:

  enumerator I2C_SLAVE_WRITE_BY_MASTER
  enumerator I2C_SLAVE_READ_BY_MASTER

enum i2c_bus_mode_t

  Enum for i2c working modes.

  Values:

  enumerator I2C_BUS_MODE_MASTER

    I2C works under master mode

  enumerator I2C_BUS_MODE_SLAVE

    I2C works under slave mode

Was this page helpful?

- Thank you! We received your feedback.
- If you have any comments, fill in Espressif Documentation Feedback Form.

- We value your feedback.
- Let us know how we can improve this page by filling in Espressif Documentation Feedback Form.