Inter-Integrated Circuit (I2C)

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 has 2 I2C controller (also called port), responsible for handling communication on the I2C bus. A single I2C controller can be a master or a slave.

Typically, an I2C slave device has a 7-bit address or 10-bit address. ESP32 supports both I2C Standard-mode (Sm) and Fast-mode (Fm) which can go up to 100KHz and 400KHz 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, users are strongly recommended to choose appropriate pull-up resistors to make the frequency accurate. The recommended value for pull-up resistors usually ranges from 1K Ohms to 10K Ohms.

Keep in mind that the higher the frequency, the smaller the pull-up resistor should be (but not less than 1 KOhms). Indeed, large resistors will decline the current, which will increase the clock switching time and reduce the frequency. We usually recommend a range of 2 KOhms to 5 KOhms, but users may also need to make some adjustments depending on their current draw requirements.

I2C Clock Configuration

i2c_clock_source_t::I2C_CLK_SRC_DEFAULT: Default I2C source clock.
i2c_clock_source_t::I2C_CLK_SRC_APB: APB clock as I2C clock source.

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 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

Both I2C master bus and I2C slave bus, when supported, are represented by i2c_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 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 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 Set 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 Depth of internal transfer queue. Only valid in asynchronous transaction.
i2c_master_bus_config_t::enable_internal_pullup Enable internal pullups. Note: This is not strong enough to pullup buses under high-speed frequency. A suitable external pullup is recommended.

If the configurations in i2c_master_bus_config_t is specified, users can call i2c_new_master_bus() 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. User can choose from enumerator I2C_ADDR_BIT_LEN_7 or I2C_ADDR_BIT_LEN_10 (if supported).
i2c_device_config_t::device_address 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/read bit.
i2c_device_config_t::scl_speed_hz set the scl line frequency of this device.
i2c_device_config_t::scl_wait_us. SCL await time (in us). Usually this value should not be very small because slave stretch will happen in pretty long time. (It's possible even stretch for 12ms). Set 0 means use default reg value.

Once the i2c_device_config_t structure is populated with mandatory parameters, users can call i2c_master_bus_add_device() 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));

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 that to release the underlying hardware.

Install I2C slave device

I2C slave requires the configuration that 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 buffer length.
i2c_slave_config_t::slave_addr sets the slave address
i2c_master_bus_config_t::intr_priority Set 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)). Please pay attention that once the interrupt priority is set, it cannot be changed until i2c_del_master_bus() is called.
i2c_slave_config_t::addr_bit_len sets true if you need the slave to have a 10-bit address.

Once the i2c_slave_config_t structure is populated with mandatory parameters, users can call i2c_new_slave_device() 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 = {
    .addr_bit_len = I2C_ADDR_BIT_LEN_7,
    .clk_source = I2C_CLK_SRC_DEFAULT,
    .i2c_port = TEST_I2C_PORT,
    .send_buf_depth = 256,
    .scl_io_num = I2C_SLAVE_SCL_IO,
    .sda_io_num = I2C_SLAVE_SDA_IO,
    .slave_addr = 0x58,
};

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 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.

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 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.

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

Simple example for writing and reading from slave:

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(I2C_PORT_NUM_0, &dev_cfg, &dev_handle));
uint8_t buf[20] = {0x20};
uint8_t buffer[2];
ESP_ERROR_CHECK(i2c_master_transmit_receive(i2c_bus_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.

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 Slave Controller

After installing the i2c slave driver by i2c_new_slave_device(), ESP32 is ready to communicate with other I2C master as a slave.

I2C Slave Write

The send buffer of the I2C slave is used as a FIFO to store the data to be sent. The data will queue up until the master requests them. You can call i2c_slave_transmit() to transfer data.

Simple example for writing data to FIFO:

uint8_t *data_wr = (uint8_t *) malloc(DATA_LENGTH);

i2c_slave_config_t i2c_slv_config = {
    .addr_bit_len = I2C_ADDR_BIT_LEN_7,   // 7-bit address
    .clk_source = I2C_CLK_SRC_DEFAULT,    // set the clock source
    .i2c_port = 0,                        // set I2C port number
    .send_buf_depth = 256,                // set tx buffer length
    .scl_io_num = 2,                      // SCL gpio number
    .sda_io_num = 1,                      // SDA gpio number
    .slave_addr = 0x58,                   // slave address
};

i2c_bus_handle_t i2c_bus_handle;
ESP_ERROR_CHECK(i2c_new_slave_device(&i2c_slv_config, &i2c_bus_handle));
for (int i = 0; i < DATA_LENGTH; i++) {
    data_wr[i] = i;
}

ESP_ERROR_CHECK(i2c_slave_transmit(i2c_bus_handle, data_wr, DATA_LENGTH, 10000));

I2C Slave Read

Whenever the master writes data to the slave, the slave will automatically store data in the receive buffer. This allows the slave application to call the function i2c_slave_receive() as its own discretion. As i2c_slave_receive() is designed as a non-blocking interface. So the user needs to register callback i2c_slave_register_event_callbacks() to know when the receive has finished.

static IRAM_ATTR bool i2c_slave_rx_done_callback(i2c_slave_dev_handle_t channel, const i2c_slave_rx_done_event_data_t *edata, void *user_data)
{
    BaseType_t high_task_wakeup = pdFALSE;
    QueueHandle_t receive_queue = (QueueHandle_t)user_data;
    xQueueSendFromISR(receive_queue, edata, &high_task_wakeup);
    return high_task_wakeup == pdTRUE;
}

uint8_t *data_rd = (uint8_t *) malloc(DATA_LENGTH);
uint32_t size_rd = 0;

i2c_slave_config_t i2c_slv_config = {
    .addr_bit_len = I2C_ADDR_BIT_LEN_7,
    .clk_source = I2C_CLK_SRC_DEFAULT,
    .i2c_port = TEST_I2C_PORT,
    .send_buf_depth = 256,
    .scl_io_num = I2C_SLAVE_SCL_IO,
    .sda_io_num = I2C_SLAVE_SDA_IO,
    .slave_addr = 0x58,
};

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

s_receive_queue = xQueueCreate(1, sizeof(i2c_slave_rx_done_event_data_t));
i2c_slave_event_callbacks_t cbs = {
    .on_recv_done = i2c_slave_rx_done_callback,
};
ESP_ERROR_CHECK(i2c_slave_register_event_callbacks(slave_handle, &cbs, s_receive_queue));

i2c_slave_rx_done_event_data_t rx_data;
ESP_ERROR_CHECK(i2c_slave_receive(slave_handle, data_rd, DATA_LENGTH));
xQueueReceive(s_receive_queue, &rx_data, pdMS_TO_TICKS(10000));
// Receive done.

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, user 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 within the function). The callback functions are required to return a boolean value, to tell the ISR whether a high priority task is woke up by it.

I2C master event callbacks are listed in the i2c_master_event_callbacks_t.

Although I2C is a synchronous communication protocol, we also support asynchronous behavior by registering above callback. 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 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, user 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 within the function). The callback function has a boolean return value, to tell the caller whether a high priority task is woke up by it.

I2C slave event callbacks are listed in the i2c_slave_event_callbacks_t.

i2c_slave_event_callbacks_t::on_recv_done sets a callback function for "receive-done" event. The function prototype is declared in i2c_slave_received_callback_t.

Power Management

When the power management is enabled (i.e. CONFIG_PM_ENABLE is on), the system will adjust or stop the source clock of I2C fifo before going into light sleep, thus potentially changing the I2C signals and leading to transmitting or receiving invalid data.

However, the driver can prevent the system from changing APB frequency by acquiring a power management lock of type ESP_PM_APB_FREQ_MAX. Whenever user creates an I2C bus that has selected I2C_CLK_SRC_APB as the clock source, the driver will guarantee that the power management lock is acquired when I2C operations begin and release the lock automatically when I2C operations finish.

IRAM Safe

By default, the I2C interrupt will be deferred when the Cache is disabled for reasons like writing/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:

Enable the interrupt being serviced even when cache is disabled
Place all functions that used by the ISR into IRAM
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, user can call them from different RTOS tasks without protection by extra locks. Other public I2C APIs are not thread safe. which means the user should avoid calling them from multiple tasks, if user strongly needs to call them in multiple tasks, please add extra lock.

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.

API Reference

Header File

components/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 driver component. To declare that your component depends on driver, add the following to your CMakeLists.txt:
REQUIRES driver
or
PRIV_REQUIRES driver

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_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 whilexfer_timeout_mswas 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_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

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

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, channels in the same group must use the same clock source

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

struct i2c_master_bus_config_t::[anonymous] 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)

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 stoped and API returns error when nack is detected.

struct i2c_device_config_t::[anonymous] flags: I2C device config flags

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

Header File

components/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 driver component. To declare that your component depends on driver, add the following to your CMakeLists.txt:
REQUIRES driver
or
PRIV_REQUIRES driver

Functions

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_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.

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_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

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).

struct i2c_slave_config_t::[anonymous] 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_received_callback_t on_recv_done: I2C slave receive done callback

Header File

components/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 driver component. To declare that your component depends on driver, add the following to your CMakeLists.txt:
REQUIRES driver
or
PRIV_REQUIRES driver

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.

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

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

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 devider

uint16_t scl_low: I2C scl low period

uint16_t scl_high: I2C scl hight 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.

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 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

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

Provide feedback about this document