# Universal Asynchronous Receiver/Transmitter (UART)

[中文]

## Introduction

A Universal Asynchronous Receiver/Transmitter (UART) is a hardware feature that handles communication (i.e., timing requirements and data framing) using widely-adopted asynchronous serial communication interfaces, such as RS232, RS422, and RS485. A UART provides a widely adopted and cheap method to realize full-duplex or half-duplex data exchange among different devices.

The ESP32-C3 chip has 2 UART controllers (also referred to as port), each featuring an identical set of registers to simplify programming and for more flexibility.

Each UART controller is independently configurable with parameters such as baud rate, data bit length, bit ordering, number of stop bits, parity bit, etc. All the regular UART controllers are compatible with UART-enabled devices from various manufacturers and can also support Infrared Data Association (IrDA) protocols.

The ESP32-C3 chip also supports using DMA with UART. For details, see to UART DMA (UHCI).

## Functional Overview

The overview describes how to establish communication between an ESP32-C3 and other UART devices using the functions and data types of the UART driver. A typical programming workflow is broken down into the sections provided below:

1. Install Drivers - Allocating ESP32-C3's resources for the UART driver

2. Set Communication Parameters - Setting baud rate, data bits, stop bits, etc.

3. Set Communication Pins - Assigning pins for connection to a device

4. Run UART Communication - Sending/receiving data

5. Use Interrupts - Triggering interrupts on specific communication events

6. Deleting a Driver - Freeing allocated resources if a UART communication is no longer required

Steps 1 to 3 comprise the configuration stage. Step 4 is where the UART starts operating. Steps 5 and 6 are optional.

The UART driver's functions identify each of the UART controllers using `uart_port_t`. This identification is needed for all the following function calls.

### Install Drivers

First of all, install the driver by calling `uart_driver_install()` and specify the following parameters:

- UART port number

- Size of RX ring buffer

- Size of TX ring buffer

- Event queue size

- Pointer to store the event queue handle

- Flags to allocate an interrupt

The function allocates the required internal resources for the UART driver.

    // Setup UART buffered IO with event queue
    const int uart_buffer_size = (1024 * 2);
    QueueHandle_t uart_queue;
    // Install UART driver using an event queue here
    ESP_ERROR_CHECK(uart_driver_install(UART_NUM_1, uart_buffer_size, uart_buffer_size, 10, &uart_queue, 0));

### Set Communication Parameters

As the next step, UART communication parameters can be configured all in a single step or individually in multiple steps.

#### Single Step

Call the function `uart_param_config()` and pass to it a `uart_config_t` structure. The `uart_config_t` structure should contain all the required parameters. See the example below.

    const uart_port_t uart_num = UART_NUM_1;
    uart_config_t uart_config = {
        .baud_rate = 115200,
        .data_bits = UART_DATA_8_BITS,
        .parity = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_CTS_RTS,
        .rx_flow_ctrl_thresh = 122,
    };
    // Configure UART parameters
    ESP_ERROR_CHECK(uart_param_config(uart_num, &uart_config));

For more information on how to configure the hardware flow control options, please refer to peripherals/uart/uart_echo.

#### Multiple Steps

Configure specific parameters individually by calling a dedicated function from the table given below. These functions are also useful if re-configuring a single parameter.

Functions for Configuring specific parameters individually
Parameter to Configure | Function
--- | ---
Baud rate | `uart_set_baudrate()`
Number of transmitted bits | `uart_set_word_length()` selected out of `uart_word_length_t`
Parity control | `uart_set_parity()` selected out of `uart_parity_t`
Number of stop bits | `uart_set_stop_bits()` selected out of `uart_stop_bits_t`
Hardware flow control mode | `uart_set_hw_flow_ctrl()` selected out of `uart_hw_flowcontrol_t`
Communication mode | `uart_set_mode()` selected out of `uart_mode_t`

Each of the above functions has a `_get_` counterpart to check the currently set value. For example, to check the current baud rate value, call `uart_get_baudrate()`.

### Set Communication Pins

After setting communication parameters, configure the physical GPIO pins to which the other UART device will be connected. For this, call the function `uart_set_pin()` and specify the GPIO pin numbers to which the driver should route the TX, RX, RTS, CTS, DTR, and DSR signals. If you want to keep a currently allocated pin number for a specific signal, pass the macro `UART_PIN_NO_CHANGE`.

The same macro `UART_PIN_NO_CHANGE` should be specified for pins that will not be used.

    // Set UART pins(TX: IO4, RX: IO5, RTS: IO18, CTS: IO19, DTR: UNUSED, DSR: UNUSED)
    ESP_ERROR_CHECK(uart_set_pin(UART_NUM_1, 4, 5, 18, 19, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE));

### Run UART Communication

Serial communication is controlled by each UART controller's finite state machine (FSM).

The process of sending data involves the following steps:

1. Write data into TX FIFO buffer

2. FSM serializes the data

3. FSM sends the data out

The process of receiving data is similar, but the steps are reversed:

1. FSM processes an incoming serial stream and parallelizes it

2. FSM writes the data into RX FIFO buffer

3. Read the data from RX FIFO buffer

Therefore, an application only writes and reads data from a specific buffer using `uart_write_bytes()` and `uart_read_bytes()` respectively, and the FSM does the rest.

#### Transmit Data

After preparing the data for transmission, call the function `uart_write_bytes()` and pass the data buffer's address and data length to it. The function copies the data to the TX ring buffer (either immediately or after enough space is available), and then exit. When there is free space in the TX FIFO buffer, an interrupt service routine (ISR) moves the data from the TX ring buffer to the TX FIFO buffer in the background. The code below demonstrates the use of this function.

    // Write data to UART.
    char* test_str = "This is a test string.\n";
    uart_write_bytes(uart_num, (const char*)test_str, strlen(test_str));

The function `uart_write_bytes_with_break()` is similar to `uart_write_bytes()` but adds a serial break signal at the end of the transmission. A 'serial break signal' means holding the TX line low for a period longer than one data frame.

    // Write data to UART, end with a break signal.
    uart_write_bytes_with_break(uart_num, "test break\n",strlen("test break\n"), 100);

Another function for writing data to the TX FIFO buffer is `uart_tx_chars()`. Unlike `uart_write_bytes()`, this function does not block until space is available. Instead, it writes all data which can immediately fit into the hardware TX FIFO, and then return the number of bytes that were written.

There is a 'companion' function `uart_wait_tx_done()` that monitors the status of the TX FIFO buffer and returns once it is empty.

    // Wait for packet to be sent
    const uart_port_t uart_num = UART_NUM_1;
    ESP_ERROR_CHECK(uart_wait_tx_done(uart_num, 100)); // wait timeout is 100 RTOS ticks (TickType_t)

#### Receive Data

Once the data is received by the UART and saved in the RX FIFO buffer, it needs to be retrieved using the function `uart_read_bytes()`. Before reading data, you can check the number of bytes available in the RX FIFO buffer by calling `uart_get_buffered_data_len()`. An example of using these functions is given below.

    // Read data from UART.
    const uart_port_t uart_num = UART_NUM_1;
    uint8_t data[128];
    int length = 0;
    ESP_ERROR_CHECK(uart_get_buffered_data_len(uart_num, (size_t*)&length));
    length = uart_read_bytes(uart_num, data, length, 100);

If the data in the RX FIFO buffer is no longer needed, you can clear the buffer by calling `uart_flush()`.

#### Software Flow Control

If the hardware flow control is disabled, you can manually set the RTS and DTR signal levels by using the functions `uart_set_rts()` and `uart_set_dtr()` respectively.

#### Communication Mode Selection

The UART controller supports a number of communication modes. A mode can be selected using the function `uart_set_mode()`. Once a specific mode is selected, the UART driver handles the behavior of a connected UART device accordingly. As an example, it can control the RS485 driver chip using the RTS line to allow half-duplex RS485 communication.

    // Setup UART in rs485 half duplex mode
    ESP_ERROR_CHECK(uart_set_mode(uart_num, UART_MODE_RS485_HALF_DUPLEX));

### Use Interrupts

There are many interrupts that can be generated depending on specific UART states or detected errors. The full list of available interrupts is provided in ESP32-C3 Technical Reference Manual > UART Controller (UART) > UART Interrupts [PDF]. You can enable or disable specific interrupts by calling `uart_enable_intr_mask()` or `uart_disable_intr_mask()` respectively.

The UART driver provides a convenient way to handle specific interrupts by wrapping them into corresponding events. Events defined in `uart_event_type_t` can be reported to a user application using the FreeRTOS queue functionality.

To receive the events that have happened, call `uart_driver_install()` and get the event queue handle returned from the function. Please see the above code snippet as an example.

The processed events include the following:

- FIFO overflow (`UART_FIFO_OVF`): The RX FIFO can trigger an interrupt when it receives more data than the FIFO can store.

  > - (Optional) Configure the full threshold of the FIFO space by entering it in the structure `uart_intr_config_t` and call `uart_intr_config()` to set the configuration. This can help the data stored in the RX FIFO can be processed timely in the driver to avoid FIFO overflow.

  > - Enable the interrupts using the functions `uart_enable_rx_intr()`.

  > - Disable these interrupts using the corresponding functions `uart_disable_rx_intr()`.

      const uart_port_t uart_num = UART_NUM_1;
      // Configure a UART interrupt threshold and timeout
      uart_intr_config_t uart_intr = {
          .intr_enable_mask = UART_INTR_RXFIFO_FULL | UART_INTR_RXFIFO_TOUT,
          .rxfifo_full_thresh = 100,
          .rx_timeout_thresh = 10,
      };
      ESP_ERROR_CHECK(uart_intr_config(uart_num, &uart_intr));

      // Enable UART RX FIFO full threshold and timeout interrupts
      ESP_ERROR_CHECK(uart_enable_rx_intr(uart_num));

- Pattern detection (`UART_PATTERN_DET`): An interrupt triggered on detecting a 'pattern' of the same character being received/sent repeatedly. It can be used, e.g., to detect a command string with a specific number of identical characters (the 'pattern') at the end. The following functions are available:

  > - Configure and enable this interrupt using `uart_enable_pattern_det_baud_intr()`

  > - Disable the interrupt using `uart_disable_pattern_det_intr()`

      //Set UART pattern detect function
      uart_enable_pattern_det_baud_intr(EX_UART_NUM, '+', PATTERN_CHR_NUM, 9, 0, 0);

- Other events: The UART driver can report other events such as data receiving (`UART_DATA`), ring buffer full (`UART_BUFFER_FULL`), detecting NULL after the stop bit (`UART_BREAK`), parity check error (`UART_PARITY_ERR`), and frame error (`UART_FRAME_ERR`).

The strings inside of brackets indicate corresponding event names. An example of how to handle various UART events can be found in peripherals/uart/uart_events.

### Deleting a Driver

If the communication established with `uart_driver_install()` is no longer required, the driver can be removed to free allocated resources by calling `uart_driver_delete()`.

### Macros

The API also defines several macros. For example, `UART_HW_FIFO_LEN` defines the length of hardware FIFO buffers; `UART_BITRATE_MAX` gives the maximum baud rate supported by the UART controllers, etc.

## Overview of RS485 Specific Communication 0ptions

Note

The following section uses `[UART_REGISTER_NAME].[UART_FIELD_BIT]` to refer to UART register fields/bits. For more information on a specific option bit, see ESP32-C3 Technical Reference Manual > UART Controller (UART) > Register Summary [PDF]. Use the register name to navigate to the register description and then find the field/bit.

- `UART_RS485_CONF_REG.UART_RS485_EN`: setting this bit enables RS485 communication mode support.

- `UART_RS485_CONF_REG.UART_RS485TX_RX_EN`: if this bit is set, the transmitter's output signal loops back to the receiver's input signal.

- `UART_RS485_CONF_REG.UART_RS485RXBY_TX_EN`: if this bit is set, the transmitter will still be sending data if the receiver is busy (remove collisions automatically by hardware).

The ESP32-C3's RS485 UART hardware can detect signal collisions during transmission of a datagram and generate the interrupt `UART_RS485_CLASH_INT` if this interrupt is enabled. The term collision means that a transmitted datagram is not equal to the one received on the other end. Data collisions are usually associated with the presence of other active devices on the bus or might occur due to bus errors.

The collision detection feature allows handling collisions when their interrupts are activated and triggered. The interrupts `UART_RS485_FRM_ERR_INT` and `UART_RS485_PARITY_ERR_INT` can be used with the collision detection feature to control frame errors and parity bit errors accordingly in RS485 mode. This functionality is supported in the UART driver and can be used by selecting the `UART_MODE_RS485_APP_CTRL` mode (see the function `uart_set_mode()`).

The collision detection feature can work with circuit A and circuit C (see Section Interface Connection Options). Use the function `uart_get_collision_flag()` to check if the collision detection flag has been raised. In the case of using circuit A or B, either DTR or RTS pin can be connected to the DE/~RE pin of the transceiver module to achieve half-duplex communication.

The RS485 half-duplex communication mode is supported by the UART driver and can be activated by selecting the `UART_MODE_RS485_HALF_DUPLEX` mode calling `uart_set_mode()`. The DTR line is automatically controlled by the hardware directly under RS485 half-duplex mode, while the RTS line is software-controlled by the UART driver. Once the host starts writing data to the TX FIFO buffer, the UART driver automatically asserts the RTS pin (logic 1); once the last bit of the data has been transmitted, the driver de-asserts the RTS pin (logic 0). To use this mode, the software would have to disable the hardware flow control function. Since the switching is made in the interrupt handler, comparing to DTR line, some latency is expected on RTS line.

### Interface Connection Options

This section provides example schematics to demonstrate the basic aspects of ESP32-C3's RS485 interface connection.

Note

- The schematics below do not necessarily contain all required elements.

- The analog devices ADM483 & ADM2483 are examples of common RS485 transceivers and can be replaced with other similar transceivers.

#### Circuit A: Collision Detection Circuit

            VCC ---------------+
                               |
                       +-------x-------+
            RXD <------| R             |
                       |              B|----------<> B
            TXD ------>| D    ADM483   |
    ESP                |               |     RS485 bus side
        DTR/RTS ------>| DE            |
                       |              A|----------<> A
                  +----| /RE           |
                  |    +-------x-------+
                  |            |
                 GND          GND

This circuit is preferable because it allows for collision detection and is quite simple at the same time. The receiver in the line driver is constantly enabled, which allows the UART to monitor the RS485 bus. Echo suppression is performed by the UART peripheral when the bit `UART_RS485_CONF_REG.UART_RS485TX_RX_EN` is enabled.

#### Circuit B: Manual Switching Transmitter/Receiver Without Collision Detection

            VCC ---------------+
                               |
                       +-------x-------+
            RXD <------| R             |
                       |              B|-----------<> B
            TXD ------>| D    ADM483   |
    ESP                |               |     RS485 bus side
        DTR/RTS --+--->| DE            |
                  |    |              A|-----------<> A
                  +----| /RE           |
                       +-------x-------+
                               |
                              GND

This circuit does not allow for collision detection. It suppresses the null bytes that the hardware receives when the bit `UART_RS485_CONF_REG.UART_RS485TX_RX_EN` is set. The bit `UART_RS485_CONF_REG.UART_RS485RXBY_TX_EN` is not applicable in this case.

#### Circuit C: Auto Switching Transmitter/Receiver

     VCC1 <-------------------+-----------+           +-------------------+----> VCC2
                   10K ____   |           |           |                   |
                  +---|____|--+       +---x-----------x---+    10K ____   |
                  |                   |                   |   +---|____|--+
    RX <----------+-------------------| RXD               |   |
                       10K ____       |                  A|---+---------------<> A (+)
                  +-------|____|------| PV    ADM2483     |   |    ____  120
                  |   ____            |                   |   +---|____|---+  RS485 bus side
          VCC1 <--+--|____|--+------->| DE                |                |
                  10K        |        |                  B|---+------------+--<> B (-)
                          ---+    +-->| /RE               |   |    ____
             10K          |       |   |                   |   +---|____|---+
            ____       | /-C      +---| TXD               |    10K         |
    TX >---|____|--+_B_|/   NPN   |   |                   |                |
                       |\         |   +---x-----------x---+                |
                       | \-E      |       |           |                    |
                          |       |       |           |                    |
                         GND1    GND1    GND1        GND2                 GND2

This galvanically isolated circuit does not require RTS pin control by a software application or driver because it controls the transceiver direction automatically. However, it requires suppressing null bytes during transmission by setting `UART_RS485_CONF_REG.UART_RS485RXBY_TX_EN` to 1 and `UART_RS485_CONF_REG.UART_RS485TX_RX_EN` to 0. This setup can work in any RS485 UART mode or even in `UART_MODE_UART`.

## Application Examples

- peripherals/uart/uart_async_rxtxtasks demonstrates how to use two asynchronous tasks for communication via the same UART interface, with one task transmitting "Hello world" periodically and the other task receiving and printing data from the UART.

- peripherals/uart/uart_echo demonstrates how to use the UART interfaces to echo back any data received on the configured UART.

- peripherals/uart/uart_echo_rs485 demonstrates how to use the ESP32's UART software driver in RS485 half duplex transmission mode to echo any data it receives on UART port back to the sender in the RS485 network, requiring external connection of bus drivers.

- peripherals/uart/uart_events demonstrates how to use the UART driver to handle special UART events, read data from UART0, and echo it back to the monitoring console.

- peripherals/uart/uart_repl demonstrates how to use and connect two UARTs, allowing the UART used for stdout to send commands and receive replies from another console UART without human interaction.

- peripherals/uart/uart_select demonstrates the use of `select()` for synchronous I/O multiplexing on the UART interface, allowing for non-blocking read and write from/to various sources such as UART and sockets, where a ready resource can be served without being blocked by a busy resource.

- peripherals/uart/nmea0183_parser demonstrates how to parse NMEA-0183 data streams from GPS/BDS/GLONASS modules using the ESP UART Event driver and ESP event loop library, and output common information such as UTC time, latitude, longitude, altitude, and speed.

## API Reference

### Header File

- components/esp_driver_uart/include/driver/uart.h

- This header file can be included with:

  >     #include "driver/uart.h"

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

  >     REQUIRES esp_driver_uart

  > or

  >     PRIV_REQUIRES esp_driver_uart

### Functions

esp_err_t uart_driver_install(uart_port_t uart_num, int rx_buffer_size, int tx_buffer_size, int queue_size, QueueHandle_t *uart_queue, int intr_alloc_flags)

  Install UART driver and set the UART to the default configuration.

  UART ISR handler will be attached to the same CPU core that this function is running on.

  Note

  Rx_buffer_size should be greater than UART_HW_FIFO_LEN(uart_num). Tx_buffer_size should be either zero or greater than UART_HW_FIFO_LEN(uart_num).

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - rx_buffer_size -- UART RX ring buffer size.

    - tx_buffer_size -- UART TX ring buffer size. If set to zero, driver will not use TX buffer, TX function will block task until all data have been sent out.

    - queue_size -- UART event queue size/depth.

    - uart_queue -- UART event queue handle (out param). On success, a new queue handle is written here to provide access to UART events. If set to NULL, driver will not use an event queue.

    - intr_alloc_flags -- Flags used to allocate the interrupt. One or multiple (ORred) ESP_INTR_FLAG_* values. See esp_intr_alloc.h for more info. Do not set ESP_INTR_FLAG_IRAM here (the driver's ISR handler is not located in IRAM)

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_driver_delete(uart_port_t uart_num)

  Uninstall UART driver.

  Parameters:

    uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

bool uart_is_driver_installed(uart_port_t uart_num)

  Checks whether the driver is installed or not.

  Parameters:

    uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

  Returns:

    - true driver is installed

    - false driver is not installed

esp_err_t uart_set_word_length(uart_port_t uart_num, uart_word_length_t data_bit)

  Set UART data bits.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - data_bit -- UART data bits

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_get_word_length(uart_port_t uart_num, uart_word_length_t *data_bit)

  Get the UART data bit configuration.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - data_bit -- Pointer to accept value of UART data bits.

  Returns:

    - ESP_FAIL Parameter error

    - ESP_OK Success, result will be put in (*data_bit)

esp_err_t uart_set_stop_bits(uart_port_t uart_num, uart_stop_bits_t stop_bits)

  Set UART stop bits.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - stop_bits -- UART stop bits

  Returns:

    - ESP_OK Success

    - ESP_FAIL Fail

esp_err_t uart_get_stop_bits(uart_port_t uart_num, uart_stop_bits_t *stop_bits)

  Get the UART stop bit configuration.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - stop_bits -- Pointer to accept value of UART stop bits.

  Returns:

    - ESP_FAIL Parameter error

    - ESP_OK Success, result will be put in (*stop_bit)

esp_err_t uart_set_parity(uart_port_t uart_num, uart_parity_t parity_mode)

  Set UART parity mode.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - parity_mode -- the enum of uart parity configuration

  Returns:

    - ESP_FAIL Parameter error

    - ESP_OK Success

esp_err_t uart_get_parity(uart_port_t uart_num, uart_parity_t *parity_mode)

  Get the UART parity mode configuration.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - parity_mode -- Pointer to accept value of UART parity mode.

  Returns:

    - ESP_FAIL Parameter error

    - ESP_OK Success, result will be put in (*parity_mode)

esp_err_t uart_get_sclk_freq(uart_sclk_t sclk, uint32_t *out_freq_hz)

  Get the frequency of a clock source for the HP UART port.

  Parameters:

    - sclk -- Clock source

    - out_freq_hz -- [out] Output of frequency, in Hz

  Returns:

    - ESP_ERR_INVALID_ARG: if the clock source is not supported

    - otherwise ESP_OK

esp_err_t uart_set_baudrate(uart_port_t uart_num, uint32_t baudrate)

  Set desired UART baud rate.

  Note that the actual baud rate set could have a slight deviation from the user-configured value due to rounding error.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - baudrate -- UART baud rate.

  Returns:

    - ESP_FAIL Parameter error, such as baud rate unachievable

    - ESP_OK Success

esp_err_t uart_get_baudrate(uart_port_t uart_num, uint32_t *baudrate)

  Get the actual UART baud rate.

  It returns the real UART rate set in the hardware. It could have a slight deviation from the user-configured baud rate.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - baudrate -- Pointer to accept value of UART baud rate

  Returns:

    - ESP_FAIL Parameter error or the UART port is not enabled

    - ESP_OK Success, result will be put in (*baudrate)

esp_err_t uart_set_line_inverse(uart_port_t uart_num, uint32_t inverse_mask)

  Set UART line inverse mode.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - inverse_mask -- Choose the wires that need to be inverted. Using the ORred mask of `uart_signal_inv_t`

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_set_hw_flow_ctrl(uart_port_t uart_num, uart_hw_flowcontrol_t flow_ctrl, uint8_t rx_thresh)

  Set hardware flow control.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - flow_ctrl -- Hardware flow control mode

    - rx_thresh -- Threshold of Hardware RX flow control (0 ~ UART_HW_FIFO_LEN(uart_num)). Only when UART_HW_FLOWCTRL_RTS is set, will the rx_thresh value be set.

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_set_sw_flow_ctrl(uart_port_t uart_num, bool enable, uint8_t rx_thresh_xon, uint8_t rx_thresh_xoff)

  Set software flow control.

  The XON and XOFF characters are '0x11' and '0x13' respectively.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1)

    - enable -- Enable or disable software flow control feature

    - rx_thresh_xon -- Low RX FIFO water mark for TX to send XON character

    - rx_thresh_xoff -- High RX FIFO water mark for TX to send XOFF character

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_get_hw_flow_ctrl(uart_port_t uart_num, uart_hw_flowcontrol_t *flow_ctrl)

  Get the UART hardware flow control configuration.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - flow_ctrl -- Option for different flow control mode.

  Returns:

    - ESP_FAIL Parameter error

    - ESP_OK Success, result will be put in (*flow_ctrl)

esp_err_t uart_clear_intr_status(uart_port_t uart_num, uint32_t clr_mask)

  Clear UART interrupt status.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - clr_mask -- Bit mask of the interrupt status to be cleared.

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_enable_intr_mask(uart_port_t uart_num, uint32_t enable_mask)

  Set UART interrupt enable.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - enable_mask -- Bit mask of the enable bits.

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_disable_intr_mask(uart_port_t uart_num, uint32_t disable_mask)

  Clear UART interrupt enable bits.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - disable_mask -- Bit mask of the disable bits.

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_enable_rx_intr(uart_port_t uart_num)

  Enable UART RX interrupt (RX_FULL & RX_TIMEOUT INTERRUPT)

  Parameters:

    uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_disable_rx_intr(uart_port_t uart_num)

  Disable UART RX interrupt (RX_FULL & RX_TIMEOUT INTERRUPT)

  Parameters:

    uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_disable_tx_intr(uart_port_t uart_num)

  Disable UART TX interrupt (TX_FIFO_EMPTY INTERRUPT)

  Parameters:

    uart_num -- UART port number

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_enable_tx_intr(uart_port_t uart_num, int enable, int thresh)

  Enable UART TX interrupt (TX_FIFO_EMPTY INTERRUPT)

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - enable -- Set to 1 to enable the interrupt

    - thresh -- Threshold of TX FIFO empty interrupt, 0 ~ UART_HW_FIFO_LEN(uart_num). If -1 is given, threshold configuration will be skipped.

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t _uart_set_pin6(uart_port_t uart_num, int tx_io_num, int rx_io_num, int rts_io_num, int cts_io_num, int dtr_io_num, int dsr_io_num)

static inline esp_err_t _uart_set_pin4(uart_port_t uart_num, int tx_io_num, int rx_io_num, int rts_io_num, int cts_io_num)

static inline esp_err_t __uart_set_pin_invalid_args__(int dummy, ...)

esp_err_t uart_set_rts(uart_port_t uart_num, int level)

  Manually set the UART RTS pin level.

  Note

  UART must be configured with hardware flow control disabled.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - level -- 1: RTS output low (active); 0: RTS output high (block)

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_set_dtr(uart_port_t uart_num, int level)

  Manually set the UART DTR pin level.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - level -- 1: DTR output low; 0: DTR output high

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_set_tx_idle_num(uart_port_t uart_num, uint16_t idle_num)

  Set UART idle interval after tx FIFO is empty.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - idle_num --

      idle interval after tx FIFO is empty(unit: the time it takes to send one bit

      under current baudrate)

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_param_config(uart_port_t uart_num, const uart_config_t *uart_config)

  Set UART configuration parameters.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - uart_config -- UART parameter settings

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error, such as baud rate unachievable

esp_err_t uart_intr_config(uart_port_t uart_num, const uart_intr_config_t *intr_conf)

  Configure UART interrupts.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - intr_conf -- UART interrupt settings

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_wait_tx_done(uart_port_t uart_num, uint32_t ticks_to_wait)

  Wait until UART TX FIFO is empty.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - ticks_to_wait -- Timeout, count in RTOS ticks

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

    - ESP_ERR_TIMEOUT Timeout

int uart_tx_chars(uart_port_t uart_num, const char *buffer, uint32_t len)

  Send data to the UART port from a given buffer and length.

  This function will not wait for enough space in TX FIFO. It will just fill the available TX FIFO and return when the FIFO is full.

  Note

  This function should only be used when UART TX buffer is not enabled.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - buffer -- data buffer address

    - len -- data length to send

  Returns:

    - (-1) Parameter error

    - OTHERS (>=0) The number of bytes pushed to the TX FIFO

int uart_write_bytes(uart_port_t uart_num, const void *src, size_t size)

  Send data to the UART port from a given buffer and length,.

  If the UART driver's parameter 'tx_buffer_size' is set to zero: This function will not return until all the data have been sent out, or at least pushed into TX FIFO.

  Otherwise, if the 'tx_buffer_size' > 0, this function will return after copying all the data to tx ring buffer, UART ISR will then move data from the ring buffer to TX FIFO gradually.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - src -- data buffer address

    - size -- data length to send

  Returns:

    - (-1) Parameter error

    - OTHERS (>=0) The number of bytes pushed to the TX FIFO

int uart_write_bytes_with_break(uart_port_t uart_num, const void *src, size_t size, int brk_len)

  Send data to the UART port from a given buffer and length,.

  If the UART driver's parameter 'tx_buffer_size' is set to zero: This function will not return until all the data and the break signal have been sent out. After all data is sent out, send a break signal.

  Otherwise, if the 'tx_buffer_size' > 0, this function will return after copying all the data to tx ring buffer, UART ISR will then move data from the ring buffer to TX FIFO gradually. After all data sent out, send a break signal.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - src -- data buffer address

    - size -- data length to send

    - brk_len -- break signal duration(unit: the time it takes to send one bit at current baudrate)

  Returns:

    - (-1) Parameter error

    - OTHERS (>=0) The number of bytes pushed to the TX FIFO

int uart_read_bytes(uart_port_t uart_num, void *buf, uint32_t length, uint32_t ticks_to_wait)

  UART read bytes from UART buffer.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - buf -- pointer to the buffer.

    - length -- data length

    - ticks_to_wait -- sTimeout, count in RTOS ticks

  Returns:

    - (-1) Error

    - OTHERS (>=0) The number of bytes read from UART buffer

esp_err_t uart_flush(uart_port_t uart_num)

  Alias of uart_flush_input. UART ring buffer flush. This will discard all data in the UART RX buffer.

  Note

  Instead of waiting the data sent out, this function will clear UART rx buffer. In order to send all the data in tx FIFO, we can use uart_wait_tx_done function.

  Parameters:

    uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_flush_input(uart_port_t uart_num)

  Clear input buffer, discard all the data is in the ring-buffer.

  Note

  In order to send all the data in tx FIFO, we can use uart_wait_tx_done function.

  Parameters:

    uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_get_buffered_data_len(uart_port_t uart_num, size_t *size)

  UART get RX ring buffer cached data length.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - size -- Pointer of size_t to accept cached data length

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_get_tx_buffer_free_size(uart_port_t uart_num, size_t *size)

  UART get TX ring buffer free space size for the next data to be enqueued.

  It returns the tight conservative bound for NOSPLIT ring buffer overall enqueueable payload across up to two chunks.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - size -- Pointer of size_t to accept the free space size

  Returns:

    - ESP_OK Success

    - ESP_ERR_INVALID_ARG Parameter error

esp_err_t uart_disable_pattern_det_intr(uart_port_t uart_num)

  UART disable pattern detect function. Designed for applications like 'AT commands'. When the hardware detects a series of one same character, the interrupt will be triggered.

  Parameters:

    uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

esp_err_t uart_enable_pattern_det_baud_intr(uart_port_t uart_num, char pattern_chr, uint8_t chr_num, int chr_tout, int post_idle, int pre_idle)

  UART enable pattern detect function. Designed for applications like 'AT commands'. When the hardware detect a series of one same character, the interrupt will be triggered.

  Parameters:

    - uart_num -- UART port number.

    - pattern_chr -- character of the pattern.

    - chr_num -- number of the character, 8bit value.

    - chr_tout -- timeout of the interval between each pattern characters, 16bit value, unit is the baud-rate cycle you configured. When the duration is more than this value, it will not take this data as at_cmd char.

    - post_idle -- idle time after the last pattern character, 16bit value, unit is the baud-rate cycle you configured. When the duration is less than this value, it will not take the previous data as the last at_cmd char

    - pre_idle -- idle time before the first pattern character, 16bit value, unit is the baud-rate cycle you configured. When the duration is less than this value, it will not take this data as the first at_cmd char.

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

int uart_pattern_pop_pos(uart_port_t uart_num)

  Return the nearest detected pattern position in buffer. The positions of the detected pattern are saved in a queue, this function will dequeue the first pattern position and move the pointer to next pattern position.

  The following APIs will modify the pattern position info: uart_flush_input, uart_read_bytes, uart_driver_delete, uart_pop_pattern_pos It is the application's responsibility to ensure atomic access to the pattern queue and the rx data buffer when using pattern detect feature.

  Note

  If the RX buffer is full and flow control is not enabled, the detected pattern may not be found in the rx buffer due to overflow.

  Parameters:

    uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

  Returns:

    - (-1) No pattern found for current index or parameter error

    - others the pattern position in rx buffer.

int uart_pattern_get_pos(uart_port_t uart_num)

  Return the nearest detected pattern position in buffer. The positions of the detected pattern are saved in a queue, This function do nothing to the queue.

  The following APIs will modify the pattern position info: uart_flush_input, uart_read_bytes, uart_driver_delete, uart_pop_pattern_pos It is the application's responsibility to ensure atomic access to the pattern queue and the rx data buffer when using pattern detect feature.

  Note

  If the RX buffer is full and flow control is not enabled, the detected pattern may not be found in the rx buffer due to overflow.

  Parameters:

    uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

  Returns:

    - (-1) No pattern found for current index or parameter error

    - others the pattern position in rx buffer.

esp_err_t uart_pattern_queue_reset(uart_port_t uart_num, int queue_length)

  Allocate a new memory with the given length to save record the detected pattern position in rx buffer.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1).

    - queue_length -- Max queue length for the detected pattern. If the queue length is not large enough, some pattern positions might be lost. Set this value to the maximum number of patterns that could be saved in data buffer at the same time.

  Returns:

    - ESP_ERR_NO_MEM No enough memory

    - ESP_ERR_INVALID_STATE Driver not installed

    - ESP_FAIL Parameter error

    - ESP_OK Success

esp_err_t uart_set_mode(uart_port_t uart_num, uart_mode_t mode)

  UART set communication mode.

  Note

  This function must be executed after uart_driver_install(), when the driver object is initialized.

  Parameters:

    - uart_num -- Uart number to configure, the max port number is (UART_NUM_MAX -1).

    - mode -- UART UART mode to set

  Returns:

    - ESP_OK Success

    - ESP_ERR_INVALID_ARG Parameter error

esp_err_t uart_set_rx_full_threshold(uart_port_t uart_num, int threshold)

  Set uart threshold value for RX fifo full.

  Note

  If application is using higher baudrate and it is observed that bytes in hardware RX fifo are overwritten then this threshold can be reduced

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1)

    - threshold -- Threshold value above which RX fifo full interrupt is generated

  Returns:

    - ESP_OK Success

    - ESP_ERR_INVALID_ARG Parameter error

    - ESP_ERR_INVALID_STATE Driver is not installed

esp_err_t uart_set_tx_empty_threshold(uart_port_t uart_num, int threshold)

  Set uart threshold values for TX fifo empty.

  Parameters:

    - uart_num -- UART port number, the max port number is (UART_NUM_MAX -1)

    - threshold -- Threshold value below which TX fifo empty interrupt is generated

  Returns:

    - ESP_OK Success

    - ESP_ERR_INVALID_ARG Parameter error

    - ESP_ERR_INVALID_STATE Driver is not installed

esp_err_t uart_set_rx_timeout(uart_port_t uart_num, const uint8_t tout_thresh)

  UART set threshold timeout for TOUT feature.

  Parameters:

    - uart_num -- Uart number to configure, the max port number is (UART_NUM_MAX -1).

    - tout_thresh -- This parameter defines timeout threshold in uart symbol periods. The maximum value of threshold is 126. tout_thresh = 1, defines TOUT interrupt timeout equal to transmission time of one symbol (~11 bit) on current baudrate. If the time is expired the UART_RXFIFO_TOUT_INT interrupt is triggered. If tout_thresh == 0, the TOUT feature is disabled.

  Returns:

    - ESP_OK Success

    - ESP_ERR_INVALID_ARG Parameter error

    - ESP_ERR_INVALID_STATE Driver is not installed

esp_err_t uart_get_collision_flag(uart_port_t uart_num, bool *collision_flag)

  Returns collision detection flag for RS485 mode Function returns the collision detection flag into variable pointed by collision_flag. *collision_flag = true, if collision detected else it is equal to false. This function should be executed when actual transmission is completed (after uart_write_bytes()).

  Parameters:

    - uart_num -- Uart number to configure the max port number is (UART_NUM_MAX -1).

    - collision_flag -- Pointer to variable of type bool to return collision flag.

  Returns:

    - ESP_OK Success

    - ESP_ERR_INVALID_ARG Parameter error

esp_err_t uart_set_wakeup_threshold(uart_port_t uart_num, int wakeup_threshold)

  Set the number of RX pin signal edges for light sleep wakeup.

  UART can be used to wake up the system from light sleep. This feature works by counting the number of positive edges on RX pin and comparing the count to the threshold. When the count exceeds the threshold, system is woken up from light sleep. This function allows setting the threshold value.

  Stop bit and parity bits (if enabled) also contribute to the number of edges. For example, letter 'a' with ASCII code 97 is encoded as 0100001101 on the wire (with 8n1 configuration), start and stop bits included. This sequence has 3 positive edges (transitions from 0 to 1). Therefore, to wake up the system when 'a' is sent, set wakeup_threshold=3.

  The character that triggers wakeup is not received by UART (i.e. it can not be obtained from UART FIFO). Depending on the baud rate, a few characters after that will also not be received. Note that when the chip enters and exits light sleep mode, APB frequency will be changing. To ensure that UART has correct Baud rate all the time, it is necessary to select a source clock which has a fixed frequency and remains active during sleep. For the supported clock sources of the chips, please refer to `uart_sclk_t` or `soc_periph_uart_clk_src_legacy_t`

  Note

  in ESP32, the wakeup signal can only be input via IO_MUX (i.e. GPIO3 should be configured as function_1 to wake up UART0, GPIO9 should be configured as function_5 to wake up UART1), UART2 does not support light sleep wakeup feature.

  Parameters:

    - uart_num -- UART number, the max port number is (UART_NUM_MAX -1).

    - wakeup_threshold -- number of RX edges for light sleep wakeup, value is 3 .. 0x3ff.

  Returns:

    - ESP_OK on success

    - ESP_ERR_INVALID_ARG if uart_num is incorrect or wakeup_threshold is outside of [3, 0x3ff] range.

esp_err_t uart_get_wakeup_threshold(uart_port_t uart_num, int *out_wakeup_threshold)

  Get the number of RX pin signal edges for light sleep wakeup.

  See description of uart_set_wakeup_threshold for the explanation of UART wakeup feature.

  Parameters:

    - uart_num -- UART number, the max port number is (UART_NUM_MAX -1).

    - out_wakeup_threshold -- [out] output, set to the current value of wakeup threshold for the given UART.

  Returns:

    - ESP_OK on success

    - ESP_ERR_INVALID_ARG if out_wakeup_threshold is NULL

esp_err_t uart_wait_tx_idle_polling(uart_port_t uart_num)

  Wait until UART tx memory empty and the last char send ok (polling mode).

  Returns:

    - ESP_OK on success

    - ESP_ERR_INVALID_ARG Parameter error

    - ESP_FAIL Driver not installed

  Parameters:

    uart_num -- UART number

esp_err_t uart_set_loop_back(uart_port_t uart_num, bool loop_back_en)

  Configure TX signal loop back to RX module, just for the test usage.

  Returns:

    - ESP_OK on success

    - ESP_ERR_INVALID_ARG Parameter error

    - ESP_FAIL Driver not installed

  Parameters:

    - uart_num -- UART number

    - loop_back_en -- Set true to enable the loop back function, else set it false.

void uart_set_always_rx_timeout(uart_port_t uart_num, bool always_rx_timeout_en)

  Configure behavior of UART RX timeout interrupt.

  When always_rx_timeout is true, timeout interrupt is triggered even if FIFO is full. This function can cause extra timeout interrupts triggered only to send the timeout event. Call this function only if you want to ensure timeout interrupt will always happen after a byte stream.

  Parameters:

    - uart_num -- UART number

    - always_rx_timeout_en -- Set to false enable the default behavior of timeout interrupt, set it to true to always trigger timeout interrupt.

esp_err_t uart_detect_bitrate_start(uart_port_t uart_num, const uart_bitrate_detect_config_t *config)

  Start to do a bitrate detection for an incoming data signal (auto baud rate detection)

  This function can act as a standalone API. No need to install UART driver before calling this function.

  It is recommended that the incoming data line contains alternating bit sequence, data bytes such as `0x55` or `0xAA`. Characters ‘NULL’, `0xCC` are not good for the measurement.

  Parameters:

    - uart_num -- The ID of the UART port to be used to do the measurement. Note that only HP UART ports have the capability.

    - config -- Pointer to the configuration structure for the UART port. If the port has already been acquired, this parameter is ignored.

  Returns:

    - ESP_OK on success

    - ESP_ERR_INVALID_ARG Parameter error

    - ESP_FAIL No free uart port or source_clk invalid

esp_err_t uart_detect_bitrate_stop(uart_port_t uart_num, bool deinit, uart_bitrate_res_t *ret_res)

  Stop the bitrate detection.

  The measurement period should last for at least one-byte long if detecting UART baud rate, then call this function to stop and get the measurement result.

  Parameters:

    - uart_num -- The ID of the UART port

    - deinit -- Whether to release the UART port after finishing the measurement

    - ret_res -- [out] Structure to store the measurement results

  Returns:

    - ESP_OK on success

    - ESP_ERR_INVALID_ARG Parameter error

    - ESP_FAIL Unknown tick frequency

### Structures

struct uart_config_t

  UART configuration parameters for uart_param_config function.

  Public Members

  int baud_rate

    UART baud rate Note that the actual baud rate set could have a slight deviation from the user-configured value due to rounding error

  uart_word_length_t data_bits

    UART byte size

  uart_parity_t parity

    UART parity mode

  uart_stop_bits_t stop_bits

    UART stop bits

  uart_hw_flowcontrol_t flow_ctrl

    UART HW flow control mode (cts/rts)

  uint8_t rx_flow_ctrl_thresh

    UART HW RTS threshold

  uart_sclk_t source_clk

    UART source clock selection

  uint32_t allow_pd

    If set, driver allows the power domain to be powered off when system enters sleep mode. This can save power, but at the expense of more RAM being consumed to save register context.

  uint32_t backup_before_sleep

    Deprecated:

      , same meaning as allow_pd

  struct uart_config_t flags

    Configuration flags

struct uart_intr_config_t

  UART interrupt configuration parameters for uart_intr_config function.

  Public Members

  uint32_t intr_enable_mask

    UART interrupt enable mask, choose from UART_XXXX_INT_ENA_M under UART_INT_ENA_REG(i), connect with bit-or operator

  uint8_t rx_timeout_thresh

    UART timeout interrupt threshold (unit: time of sending one byte)

  uint8_t txfifo_empty_intr_thresh

    UART TX empty interrupt threshold.

  uint8_t rxfifo_full_thresh

    UART RX full interrupt threshold.

struct uart_event_t

  Event structure used in UART event queue.

  Public Members

  uart_event_type_t type

    UART event type

  size_t size

    UART data size for UART_DATA event

  bool timeout_flag

    UART data read timeout flag for UART_DATA event (no new data received during configured RX TOUT) If the event is caused by FIFO-full interrupt, then there will be no event with the timeout flag before the next byte coming.

struct uart_bitrate_detect_config_t

  UART bitrate detection configuration parameters for `uart_detect_bitrate_start` function to acquire a new uart handle.

  Public Members

  int rx_io_num

    GPIO pin number for the incoming signal

  uart_sclk_t source_clk

    The higher the frequency of the clock source, the more accurate the detected bitrate value; The slower the frequency of the clock source, the slower the bitrate can be measured

struct uart_bitrate_res_t

  Structure to store the measurement results for UART bitrate detection within the measurement period.

  Formula to calculate the bitrate: If the signal is ideal, bitrate = clk_freq_hz * 2 / (low_period + high_period) If the signal is weak along falling edges, then you may use bitrate = clk_freq_hz * 2 / pos_period If the signal is weak along rising edges, then you may use bitrate = clk_freq_hz * 2 / neg_period

  Public Members

  uint32_t low_period

    Stores the minimum tick count of a low-level pulse

  uint32_t high_period

    Stores the minimum tick count of a high-level pulse

  uint32_t pos_period

    Stores the minimum tick count between two positive edges

  uint32_t neg_period

    Stores the minimum tick count between two negative edges

  uint32_t edge_cnt

    Stores the count of RX edge changes (10-bit counter, be careful, it could overflow)

  uint32_t clk_freq_hz

    The frequency of the tick being used to count the measurement results, in Hz

### Macros

UART_PIN_NO_CHANGE

UART_HW_FIFO_LEN(uart_num)

  Length of the UART HW FIFO.

UART_BITRATE_MAX

  Maximum configurable bitrate.

_GET_UART_SET_PIN_FUNC_NAME(_1, _2, _3, _4, _5, _6, _7, _FUNC_NAME, ...)

uart_set_pin(...)

  Assign signals of a UART peripheral to GPIO pins.

  Note

  If the GPIO number configured for a UART signal matches one of the IOMUX signals for that GPIO, the signal will be connected directly via the IOMUX. Otherwise the GPIO and signal will be connected via the GPIO Matrix. For example, if on an ESP32 the call `uart_set_pin(0, 1, 3, -1, -1)` is performed, as GPIO1 is UART0's default TX pin and GPIO3 is UART0's default RX pin, both will be connected to respectively U0TXD and U0RXD through the IOMUX, totally bypassing the GPIO matrix. The check is performed on a per-pin basis. Thus, it is possible to have RX pin binded to a GPIO through the GPIO matrix, whereas TX is binded to its GPIO through the IOMUX.

  Note

  It is possible to configure TX and RX to share the same IO (single wire mode), but please be aware of output conflict, which could damage the pad. Apply open-drain and pull-up to the pad ahead of time as a protection, or the upper layer protocol must guarantee no output from two ends at the same time.

  Note

  Variadic arguments

  - param: uart_num UART port number, the max port number is (UART_NUM_MAX -1).

  - param: tx_io_num UART TX pin GPIO number.

  - param: rx_io_num UART RX pin GPIO number.

  - param: rts_io_num UART RTS pin GPIO number.

  - param: cts_io_num UART CTS pin GPIO number.

  - param: dtr_io_num UART DTR pin GPIO number (optional). DTR signal is automatically controlled by hardware when UART is in RS485 mode.

  - param: dsr_io_num UART DSR pin GPIO number (optional).

  Returns:

    - ESP_OK Success

    - ESP_FAIL Parameter error

### Enumerations

enum uart_event_type_t

  UART event types used in the ring buffer.

  Values:

  enumerator UART_DATA

    Triggered when the receiver either takes longer than rx_timeout_thresh to receive a byte, or when more data is received than what rxfifo_full_thresh specifies

  enumerator UART_BREAK

    Triggered when the receiver detects a NULL character

  enumerator UART_BUFFER_FULL

    Triggered when RX ring buffer is full

  enumerator UART_FIFO_OVF

    Triggered when the received data exceeds the capacity of the RX FIFO

  enumerator UART_FRAME_ERR

    Triggered when the receiver detects a data frame error

  enumerator UART_PARITY_ERR

    Triggered when a parity error is detected in the received data

  enumerator UART_DATA_BREAK

    Internal event triggered to signal a break afte data transmission

  enumerator UART_PATTERN_DET

    Triggered when a specified pattern is detected in the incoming data

  enumerator UART_WAKEUP

    Triggered when a wakeup signal is detected

  enumerator UART_EVENT_MAX

    Maximum index for UART events

### Header File

- components/esp_driver_uart/include/driver/uart_wakeup.h

- This header file can be included with:

  >     #include "driver/uart_wakeup.h"

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

  >     REQUIRES esp_driver_uart

  > or

  >     PRIV_REQUIRES esp_driver_uart

### Functions

esp_err_t uart_wakeup_setup(uart_port_t uart_num, const uart_wakeup_cfg_t *cfg)

  Initializes the UART wakeup functionality.

  This function configures the wakeup behavior for a specified UART port based on the provided configuration. The behavior depends on the selected wakeup mode and additional parameters such as active threshold or character sequence, if applicable. It is important that the provided configuration matches the capabilities of the SOC to ensure proper operation.

  Parameters:

    - uart_num -- The UART port to initialize for wakeup (e.g., UART_NUM_0, UART_NUM_1, etc.).

    - cfg -- Pointer to the `uart_wakeup_cfg_t` structure that contains the wakeup configuration settings.

  Returns:

    - `ESP_OK` if the wakeup configuration was successfully applied.

    - `ESP_ERR_INVALID_ARG` if the provided configuration is invalid (e.g., threshold values out of range).

esp_err_t uart_wakeup_clear(uart_port_t uart_num, uart_wakeup_mode_t wakeup_mode)

  Clear the UART wakeup configuration.

  This function will clear the UART wakeup behavior and set to its default configuration.

  Parameters:

    - uart_num -- The UART port to initialize for wakeup (e.g., UART_NUM_0, UART_NUM_1, etc.).

    - wakeup_mode -- The UART wakeup mode set in `uart_wakeup_setup`.

  Returns:

    - `ESP_OK` Clear wakeup configuration successfully.

### Structures

struct uart_wakeup_cfg_t

  Structure that holds configuration for UART wakeup.

  This structure is used to configure the wakeup behavior for a UART port. The wakeup mode can be selected from several options, such as active threshold, FIFO threshold, start bit detection, and character sequence detection. The availability of different wakeup modes depends on the SOC capabilities.

  Public Members

  uart_wakeup_mode_t wakeup_mode

    Wakeup mode selection

  uint16_t rx_edge_threshold

    Used in Active threshold wake-up; related: UART_WK_MODE_ACTIVE_THRESH; Configures the number of RXD edge changes to wake up the chip.

### Header File

- components/esp_hal_uart/include/hal/uart_types.h

- This header file can be included with:

  >     #include "hal/uart_types.h"

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

  >     REQUIRES esp_hal_uart

  > or

  >     PRIV_REQUIRES esp_hal_uart

### Structures

struct uart_at_cmd_t

  UART AT cmd char configuration parameters Note that this function may different on different chip. Please refer to the TRM at confirguration.

  Public Members

  uint8_t cmd_char

    UART AT cmd char

  uint8_t char_num

    AT cmd char repeat number

  uint32_t gap_tout

    gap time(in baud-rate) between AT cmd char

  uint32_t pre_idle

    the idle time(in baud-rate) between the non AT char and first AT char

  uint32_t post_idle

    the idle time(in baud-rate) between the last AT char and the none AT char

struct uart_sw_flowctrl_t

  UART software flow control configuration parameters.

  Public Members

  uint8_t xon_char

    Xon flow control char

  uint8_t xoff_char

    Xoff flow control char

  uint8_t xon_thrd

    If the software flow control is enabled and the data amount in rxfifo is less than xon_thrd, an xon_char will be sent

  uint8_t xoff_thrd

    If the software flow control is enabled and the data amount in rxfifo is more than xoff_thrd, an xoff_char will be sent

### Type Definitions

typedef soc_periph_uart_clk_src_legacy_t uart_sclk_t

  UART source clock.

### Enumerations

enum uart_port_t

  UART port number, can be UART_NUM_0 ~ (UART_NUM_MAX -1).

  Values:

  enumerator UART_NUM_0

    UART port 0

  enumerator UART_NUM_1

    UART port 1

  enumerator UART_NUM_MAX

    UART port max

enum uart_mode_t

  UART mode selection.

  Values:

  enumerator UART_MODE_UART

    mode: regular UART mode

  enumerator UART_MODE_RS485_HALF_DUPLEX

    mode: half duplex RS485 UART mode control by RTS pin

  enumerator UART_MODE_IRDA

    mode: IRDA UART mode

  enumerator UART_MODE_RS485_COLLISION_DETECT

    mode: RS485 collision detection UART mode (used for test purposes)

  enumerator UART_MODE_RS485_APP_CTRL

    mode: application control RS485 UART mode (used for test purposes)

enum uart_word_length_t

  UART word length constants.

  Values:

  enumerator UART_DATA_5_BITS

    word length: 5bits

  enumerator UART_DATA_6_BITS

    word length: 6bits

  enumerator UART_DATA_7_BITS

    word length: 7bits

  enumerator UART_DATA_8_BITS

    word length: 8bits

  enumerator UART_DATA_BITS_MAX

enum uart_stop_bits_t

  UART stop bits number.

  Values:

  enumerator UART_STOP_BITS_1

    stop bit: 1bit

  enumerator UART_STOP_BITS_1_5

    stop bit: 1.5bits

  enumerator UART_STOP_BITS_2

    stop bit: 2bits

  enumerator UART_STOP_BITS_MAX

enum uart_parity_t

  UART parity constants.

  Values:

  enumerator UART_PARITY_DISABLE

    Disable UART parity

  enumerator UART_PARITY_EVEN

    Enable UART even parity

  enumerator UART_PARITY_ODD

    Enable UART odd parity

enum uart_hw_flowcontrol_t

  UART hardware flow control modes.

  Values:

  enumerator UART_HW_FLOWCTRL_DISABLE

    disable hardware flow control

  enumerator UART_HW_FLOWCTRL_RTS

    enable RX hardware flow control (rts)

  enumerator UART_HW_FLOWCTRL_CTS

    enable TX hardware flow control (cts)

  enumerator UART_HW_FLOWCTRL_CTS_RTS

    enable hardware flow control

  enumerator UART_HW_FLOWCTRL_MAX

enum uart_signal_inv_t

  UART signal bit map.

  Values:

  enumerator UART_SIGNAL_INV_DISABLE

    Disable UART signal inverse

  enumerator UART_SIGNAL_IRDA_TX_INV

    inverse the UART irda_tx signal

  enumerator UART_SIGNAL_IRDA_RX_INV

    inverse the UART irda_rx signal

  enumerator UART_SIGNAL_RXD_INV

    inverse the UART rxd signal

  enumerator UART_SIGNAL_CTS_INV

    inverse the UART cts signal

  enumerator UART_SIGNAL_DSR_INV

    inverse the UART dsr signal

  enumerator UART_SIGNAL_TXD_INV

    inverse the UART txd signal

  enumerator UART_SIGNAL_RTS_INV

    inverse the UART rts signal

  enumerator UART_SIGNAL_DTR_INV

    inverse the UART dtr signal

enum uart_wakeup_mode_t

  Enumeration of UART wake-up modes.

  Values:

  enumerator UART_WK_MODE_ACTIVE_THRESH

    Wake-up triggered by active edge threshold

### GPIO Lookup Macros

Some UART ports have dedicated IO_MUX pins to which they are connected directly. These can be useful if you need very high UART baud rates, which means you will have to use IO_MUX pins only. In other cases, any GPIO pin can be used for UART communication by routing the signals through the GPIO matrix. If the UART port has dedicated IO_MUX pins, `UxTXD_GPIO_NUM` and `UxRXD_GPIO_NUM` can be used to find the corresponding IO_MUX pin numbers.

### Header File

- components/soc/esp32c3/include/soc/uart_pins.h

- This header file can be included with:

  >     #include "soc/uart_pins.h"

### Macros

U0RXD_GPIO_NUM

U0TXD_GPIO_NUM

U0RTS_GPIO_NUM

U0CTS_GPIO_NUM

U0DTR_GPIO_NUM

U0DSR_GPIO_NUM

U1RXD_GPIO_NUM

U1TXD_GPIO_NUM

U1RTS_GPIO_NUM

U1CTS_GPIO_NUM

U1DTR_GPIO_NUM

U1DSR_GPIO_NUM

U0TXD_MUX_FUNC

U0RXD_MUX_FUNC

U0RTS_MUX_FUNC

U0CTS_MUX_FUNC

U0DTR_MUX_FUNC

U0DSR_MUX_FUNC

U1TXD_MUX_FUNC

U1RXD_MUX_FUNC

U1RTS_MUX_FUNC

U1CTS_MUX_FUNC

U1DTR_MUX_FUNC

U1DSR_MUX_FUNC

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