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Universal Asynchronous Receiver-Transmitter (UART)

Overview

Zephyr provides three different ways to access the UART peripheral. Depending on the method, different API functions are used according to below sections:

  1. Polling API

  2. Interrupt-driven API

  3. Asynchronous API using Direct Memory Access (DMA)

Polling is the most basic method to access the UART peripheral. The reading function, uart_poll_in, is a non-blocking function and returns a character or -1 when no valid data is available. The writing function, uart_poll_out, is a blocking function and the thread waits until the given character is sent.

With the Interrupt-driven API, possibly slow communication can happen in the background while the thread continues with other tasks. The Kernel’s Data Passing features can be used to communicate between the thread and the UART driver.

The Asynchronous API allows to read and write data in the background using DMA without interrupting the MCU at all. However, the setup is more complex than the other methods.

Warning

Interrupt-driven API and the Asynchronous API should NOT be used at the same time for the same hardware peripheral, since both APIs require hardware interrupts to function properly. Using the callbacks for both APIs would result in interference between each other. CONFIG_UART_EXCLUSIVE_API_CALLBACKS is enabled by default so that only the callbacks associated with one API is active at a time.

Configuration Options

Most importantly, the Kconfig options define whether the polling API (default), the interrupt-driven API or the asynchronous API can be used. Only enable the features you need in order to minimize memory footprint.

Related configuration options:

API Reference

Related code samples

802.15.4 "serial-radio"

Implement a slip-radio device for Contiki-based border routers.

Native TTY UART

Use native TTY driver to send and receive data between two UART-to-USB bridge dongles.

STM32 single-wire UART

Use single-wire/half-duplex UART functionality of STM32 devices.

UART Passthrough

Pass data directly between the console and another UART interface.

UART echo

Read data from the console and echo it back.

USB CDC-ACM

Use USB CDC-ACM driver to implement a serial port echo.

group uart_interface

UART Interface.

Since

1.0

Version

1.0.0

Enums

enum uart_line_ctrl

Line control signals.

Values:

enumerator UART_LINE_CTRL_BAUD_RATE = BIT(0)

Baud rate.

enumerator UART_LINE_CTRL_RTS = BIT(1)

Request To Send (RTS)

enumerator UART_LINE_CTRL_DTR = BIT(2)

Data Terminal Ready (DTR)

enumerator UART_LINE_CTRL_DCD = BIT(3)

Data Carrier Detect (DCD)

enumerator UART_LINE_CTRL_DSR = BIT(4)

Data Set Ready (DSR)

enum uart_rx_stop_reason

Reception stop reasons.

Values that correspond to events or errors responsible for stopping receiving.

Values:

enumerator UART_ERROR_OVERRUN = (1 << 0)

Overrun error.

enumerator UART_ERROR_PARITY = (1 << 1)

Parity error.

enumerator UART_ERROR_FRAMING = (1 << 2)

Framing error.

enumerator UART_BREAK = (1 << 3)

Break interrupt.

A break interrupt was received. This happens when the serial input is held at a logic ‘0’ state for longer than the sum of start time + data bits + parity + stop bits.

enumerator UART_ERROR_COLLISION = (1 << 4)

Collision error.

This error is raised when transmitted data does not match received data. Typically this is useful in scenarios where the TX and RX lines maybe connected together such as RS-485 half-duplex. This error is only valid on UARTs that support collision checking.

enumerator UART_ERROR_NOISE = (1 << 5)

Noise error.

enum uart_config_parity

Parity modes.

Values:

enumerator UART_CFG_PARITY_NONE

No parity.

enumerator UART_CFG_PARITY_ODD

Odd parity.

enumerator UART_CFG_PARITY_EVEN

Even parity.

enumerator UART_CFG_PARITY_MARK

Mark parity.

enumerator UART_CFG_PARITY_SPACE

Space parity.

enum uart_config_stop_bits

Number of stop bits.

Values:

enumerator UART_CFG_STOP_BITS_0_5

0.5 stop bit

enumerator UART_CFG_STOP_BITS_1

1 stop bit

enumerator UART_CFG_STOP_BITS_1_5

1.5 stop bits

enumerator UART_CFG_STOP_BITS_2

2 stop bits

enum uart_config_data_bits

Number of data bits.

Values:

enumerator UART_CFG_DATA_BITS_5

5 data bits

enumerator UART_CFG_DATA_BITS_6

6 data bits

enumerator UART_CFG_DATA_BITS_7

7 data bits

enumerator UART_CFG_DATA_BITS_8

8 data bits

enumerator UART_CFG_DATA_BITS_9

9 data bits

enum uart_config_flow_control

Hardware flow control options.

With flow control set to none, any operations related to flow control signals can be managed by user with uart_line_ctrl functions. In other cases, flow control is managed by hardware/driver.

Values:

enumerator UART_CFG_FLOW_CTRL_NONE

No flow control.

enumerator UART_CFG_FLOW_CTRL_RTS_CTS

RTS/CTS flow control.

enumerator UART_CFG_FLOW_CTRL_DTR_DSR

DTR/DSR flow control.

enumerator UART_CFG_FLOW_CTRL_RS485

RS485 flow control.

Functions

int uart_err_check(const struct device *dev)

Check whether an error was detected.

Parameters:

  • dev – UART device instance.

Return values:

  • 0 – If no error was detected.

  • err – Error flags as defined in uart_rx_stop_reason

  • -ENOSYS – If not implemented.

int uart_configure(const struct device *dev, const struct uart_config *cfg)

Set UART configuration.

Sets UART configuration using data from *cfg.

Parameters:

  • dev – UART device instance.

  • cfg – UART configuration structure.

Return values:

  • 0 – If successful.

  • -errno – Negative errno code in case of failure.

  • -ENOSYS – If configuration is not supported by device or driver does not support setting configuration in runtime.

  • -ENOTSUP – If API is not enabled.

int uart_config_get(const struct device *dev, struct uart_config *cfg)

Get UART configuration.

Stores current UART configuration to *cfg, can be used to retrieve initial configuration after device was initialized using data from DTS.

Parameters:

  • dev – UART device instance.

  • cfg – UART configuration structure.

Return values:

  • 0 – If successful.

  • -errno – Negative errno code in case of failure.

  • -ENOSYS – If driver does not support getting current configuration.

  • -ENOTSUP – If API is not enabled.

int uart_line_ctrl_set(const struct device *dev, uint32_t ctrl, uint32_t val)

Manipulate line control for UART.

Parameters:

  • dev – UART device instance.

  • ctrl – The line control to manipulate (see enum uart_line_ctrl).

  • val – Value to set to the line control.

Return values:

  • 0 – If successful.

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

  • -errno – Other negative errno value in case of failure.

int uart_line_ctrl_get(const struct device *dev, uint32_t ctrl, uint32_t *val)

Retrieve line control for UART.

Parameters:

  • dev – UART device instance.

  • ctrl – The line control to retrieve (see enum uart_line_ctrl).

  • val – Pointer to variable where to store the line control value.

Return values:

  • 0 – If successful.

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

  • -errno – Other negative errno value in case of failure.

int uart_drv_cmd(const struct device *dev, uint32_t cmd, uint32_t p)

Send extra command to driver.

Implementation and accepted commands are driver specific. Refer to the drivers for more information.

Parameters:

  • dev – UART device instance.

  • cmd – Command to driver.

  • p – Parameter to the command.

Return values:

  • 0 – If successful.

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

  • -errno – Other negative errno value in case of failure.

struct uart_config
#include <uart.h>

UART controller configuration structure.

Public Members

uint32_t baudrate

Baudrate setting in bps.

uint8_t parity

Parity bit, use uart_config_parity.

uint8_t stop_bits

Stop bits, use uart_config_stop_bits.

uint8_t data_bits

Data bits, use uart_config_data_bits.

uint8_t flow_ctrl

Flow control setting, use uart_config_flow_control.

Polling API

group uart_polling

Functions

int uart_poll_in(const struct device *dev, unsigned char *p_char)

Read a character from the device for input.

This routine checks if the receiver has valid data. When the receiver has valid data, it reads a character from the device, stores to the location pointed to by p_char, and returns 0 to the calling thread. It returns -1, otherwise. This function is a non-blocking call.

Parameters:

  • dev – UART device instance.

  • p_char – Pointer to character.

Return values:

  • 0 – If a character arrived.

  • -1 – If no character was available to read (i.e. the UART input buffer was empty).

  • -ENOSYS – If the operation is not implemented.

  • -EBUSY – If async reception was enabled using uart_rx_enable

int uart_poll_in_u16(const struct device *dev, uint16_t *p_u16)

Read a 16-bit datum from the device for input.

This routine checks if the receiver has valid data. When the receiver has valid data, it reads a 16-bit datum from the device, stores to the location pointed to by p_u16, and returns 0 to the calling thread. It returns -1, otherwise. This function is a non-blocking call.

Parameters:

  • dev – UART device instance.

  • p_u16 – Pointer to 16-bit data.

Return values:

  • 0 – If data arrived.

  • -1 – If no data was available to read (i.e., the UART input buffer was empty).

  • -ENOTSUP – If API is not enabled.

  • -ENOSYS – If the function is not implemented.

  • -EBUSY – If async reception was enabled using uart_rx_enable

void uart_poll_out(const struct device *dev, unsigned char out_char)

Write a character to the device for output.

This routine checks if the transmitter is full. When the transmitter is not full, it writes a character to the data register. It waits and blocks the calling thread, otherwise. This function is a blocking call.

To send a character when hardware flow control is enabled, the handshake signal CTS must be asserted.

Parameters:

  • dev – UART device instance.

  • out_char – Character to send.

void uart_poll_out_u16(const struct device *dev, uint16_t out_u16)

Write a 16-bit datum to the device for output.

This routine checks if the transmitter is full. When the transmitter is not full, it writes a 16-bit datum to the data register. It waits and blocks the calling thread, otherwise. This function is a blocking call.

To send a datum when hardware flow control is enabled, the handshake signal CTS must be asserted.

Parameters:

  • dev – UART device instance.

  • out_u16 – Wide data to send.

Interrupt-driven API

group uart_interrupt

Typedefs

typedef void (*uart_irq_callback_user_data_t)(const struct device *dev, void *user_data)

Define the application callback function signature for uart_irq_callback_user_data_set() function.

Param dev:

UART device instance.

Param user_data:

Arbitrary user data.

typedef void (*uart_irq_config_func_t)(const struct device *dev)

For configuring IRQ on each individual UART device.

Param dev:

UART device instance.

Functions

static inline int uart_fifo_fill(const struct device *dev, const uint8_t *tx_data, int size)

Fill FIFO with data.

This function is expected to be called from UART interrupt handler (ISR), if uart_irq_tx_ready() returns true. Result of calling this function not from an ISR is undefined (hardware-dependent). Likewise, not calling this function from an ISR if uart_irq_tx_ready() returns true may lead to undefined behavior, e.g. infinite interrupt loops. It’s mandatory to test return value of this function, as different hardware has different FIFO depth (oftentimes just 1).

Parameters:

  • dev – UART device instance.

  • tx_data – Data to transmit.

  • size – Number of bytes to send.

Return values:

  • -ENOSYS – if this function is not supported

  • -ENOTSUP – If API is not enabled.

Returns:

Number of bytes sent.

static inline int uart_fifo_fill_u16(const struct device *dev, const uint16_t *tx_data, int size)

Fill FIFO with wide data.

This function is expected to be called from UART interrupt handler (ISR), if uart_irq_tx_ready() returns true. Result of calling this function not from an ISR is undefined (hardware-dependent). Likewise, not calling this function from an ISR if uart_irq_tx_ready() returns true may lead to undefined behavior, e.g. infinite interrupt loops. It’s mandatory to test return value of this function, as different hardware has different FIFO depth (oftentimes just 1).

Parameters:

  • dev – UART device instance.

  • tx_data – Wide data to transmit.

  • size – Number of datum to send.

Return values:

  • -ENOSYS – If this function is not implemented

  • -ENOTSUP – If API is not enabled.

Returns:

Number of datum sent.

static inline int uart_fifo_read(const struct device *dev, uint8_t *rx_data, const int size)

Read data from FIFO.

This function is expected to be called from UART interrupt handler (ISR), if uart_irq_rx_ready() returns true. Result of calling this function not from an ISR is undefined (hardware-dependent). It’s unspecified whether “RX ready” condition as returned by uart_irq_rx_ready() is level- or edge- triggered. That means that once uart_irq_rx_ready() is detected, uart_fifo_read() must be called until it reads all available data in the FIFO (i.e. until it returns less data than was requested).

Parameters:

  • dev – UART device instance.

  • rx_data – Data container.

  • size – Container size.

Return values:

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

Returns:

Number of bytes read.

static inline int uart_fifo_read_u16(const struct device *dev, uint16_t *rx_data, const int size)

Read wide data from FIFO.

This function is expected to be called from UART interrupt handler (ISR), if uart_irq_rx_ready() returns true. Result of calling this function not from an ISR is undefined (hardware-dependent). It’s unspecified whether “RX ready” condition as returned by uart_irq_rx_ready() is level- or edge- triggered. That means that once uart_irq_rx_ready() is detected, uart_fifo_read() must be called until it reads all available data in the FIFO (i.e. until it returns less data than was requested).

Parameters:

  • dev – UART device instance.

  • rx_data – Wide data container.

  • size – Container size.

Return values:

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

Returns:

Number of datum read.

void uart_irq_tx_enable(const struct device *dev)

Enable TX interrupt in IER.

Parameters:

  • dev – UART device instance.

void uart_irq_tx_disable(const struct device *dev)

Disable TX interrupt in IER.

Parameters:

  • dev – UART device instance.

static inline int uart_irq_tx_ready(const struct device *dev)

Check if UART TX buffer can accept a new char.

Check if UART TX buffer can accept at least one character for transmission (i.e. uart_fifo_fill() will succeed and return non-zero). This function must be called in a UART interrupt handler, or its result is undefined. Before calling this function in the interrupt handler, uart_irq_update() must be called once per the handler invocation.

Parameters:

  • dev – UART device instance.

Return values:

  • 1 – If TX interrupt is enabled and at least one char can be written to UART.

  • 0 – If device is not ready to write a new byte.

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

void uart_irq_rx_enable(const struct device *dev)

Enable RX interrupt.

Parameters:

  • dev – UART device instance.

void uart_irq_rx_disable(const struct device *dev)

Disable RX interrupt.

Parameters:

  • dev – UART device instance.

static inline int uart_irq_tx_complete(const struct device *dev)

Check if UART TX block finished transmission.

Check if any outgoing data buffered in UART TX block was fully transmitted and TX block is idle. When this condition is true, UART device (or whole system) can be power off. Note that this function is not useful to check if UART TX can accept more data, use uart_irq_tx_ready() for that. This function must be called in a UART interrupt handler, or its result is undefined. Before calling this function in the interrupt handler, uart_irq_update() must be called once per the handler invocation.

Parameters:

  • dev – UART device instance.

Return values:

  • 1 – If nothing remains to be transmitted.

  • 0 – If transmission is not completed.

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

static inline int uart_irq_rx_ready(const struct device *dev)

Check if UART RX buffer has a received char.

Check if UART RX buffer has at least one pending character (i.e. uart_fifo_read() will succeed and return non-zero). This function must be called in a UART interrupt handler, or its result is undefined. Before calling this function in the interrupt handler, uart_irq_update() must be called once per the handler invocation. It’s unspecified whether condition as returned by this function is level- or edge- triggered (i.e. if this function returns true when RX FIFO is non-empty, or when a new char was received since last call to it). See description of uart_fifo_read() for implication of this.

Parameters:

  • dev – UART device instance.

Return values:

  • 1 – If a received char is ready.

  • 0 – If a received char is not ready.

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

void uart_irq_err_enable(const struct device *dev)

Enable error interrupt.

Parameters:

  • dev – UART device instance.

void uart_irq_err_disable(const struct device *dev)

Disable error interrupt.

Parameters:

  • dev – UART device instance.

int uart_irq_is_pending(const struct device *dev)

Check if any IRQs is pending.

Parameters:

  • dev – UART device instance.

Return values:

  • 1 – If an IRQ is pending.

  • 0 – If an IRQ is not pending.

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

int uart_irq_update(const struct device *dev)

Start processing interrupts in ISR.

This function should be called the first thing in the ISR. Calling uart_irq_rx_ready(), uart_irq_tx_ready(), uart_irq_tx_complete() allowed only after this.

The purpose of this function is:

  • For devices with auto-acknowledge of interrupt status on register read to cache the value of this register (rx_ready, etc. then use this case).

  • For devices with explicit acknowledgment of interrupts, to ack any pending interrupts and likewise to cache the original value.

  • For devices with implicit acknowledgment, this function will be empty. But the ISR must perform the actions needs to ack the interrupts (usually, call uart_fifo_read() on rx_ready, and uart_fifo_fill() on tx_ready).

Parameters:

  • dev – UART device instance.

Return values:

  • 1 – On success.

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

static inline int uart_irq_callback_user_data_set(const struct device *dev, uart_irq_callback_user_data_t cb, void *user_data)

Set the IRQ callback function pointer.

This sets up the callback for IRQ. When an IRQ is triggered, the specified function will be called with specified user data. See description of uart_irq_update() for the requirements on ISR.

Parameters:

  • dev – UART device instance.

  • cb – Pointer to the callback function.

  • user_data – Data to pass to callback function.

Return values:

  • 0 – On success.

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

static inline int uart_irq_callback_set(const struct device *dev, uart_irq_callback_user_data_t cb)

Set the IRQ callback function pointer (legacy).

This sets up the callback for IRQ. When an IRQ is triggered, the specified function will be called with the device pointer.

Parameters:

  • dev – UART device instance.

  • cb – Pointer to the callback function.

Return values:

  • 0 – On success.

  • -ENOSYS – If this function is not implemented.

  • -ENOTSUP – If API is not enabled.

Asynchronous API

group uart_async

Since

1.14

Version

0.8.0

Typedefs

typedef void (*uart_callback_t)(const struct device *dev, struct uart_event *evt, void *user_data)

Define the application callback function signature for uart_callback_set() function.

Param dev:

UART device instance.

Param evt:

Pointer to uart_event instance.

Param user_data:

Pointer to data specified by user.

Enums

enum uart_event_type

Types of events passed to callback in UART_ASYNC_API.

Receiving:

  1. To start receiving, uart_rx_enable has to be called with first buffer

  2. When receiving starts to current buffer, UART_RX_BUF_REQUEST will be generated, in response to that user can either:

    • Provide second buffer using uart_rx_buf_rsp, when first buffer is filled, receiving will automatically start to second buffer.

    • Ignore the event, this way when current buffer is filled UART_RX_RDY event will be generated and receiving will be stopped.

  3. If some data was received and timeout occurred UART_RX_RDY event will be generated. It can happen multiples times for the same buffer. RX timeout is counted from last byte received i.e. if no data was received, there won’t be any timeout event.

  4. UART_RX_BUF_RELEASED event will be generated when the current buffer is no longer used by the driver. It will immediately follow UART_RX_RDY event. Depending on the implementation buffer may be released when it is completely or partially filled.

  5. If there was second buffer provided, it will become current buffer and we start again at point 2. If no second buffer was specified receiving is stopped and UART_RX_DISABLED event is generated. After that whole process can be repeated.

Any time during reception UART_RX_STOPPED event can occur. if there is any data received, UART_RX_RDY event will be generated. It will be followed by UART_RX_BUF_RELEASED event for every buffer currently passed to driver and finally by UART_RX_DISABLED event.

Receiving can be disabled using uart_rx_disable, after calling that function, if there is any data received, UART_RX_RDY event will be generated. UART_RX_BUF_RELEASED event will be generated for every buffer currently passed to driver and finally UART_RX_DISABLED event will occur.

Transmitting:

  1. Transmitting starts by uart_tx function.

  2. If whole buffer was transmitted UART_TX_DONE is generated. If timeout occurred UART_TX_ABORTED will be generated.

Transmitting can be aborted using uart_tx_abort, after calling that function UART_TX_ABORTED event will be generated.

Values:

enumerator UART_TX_DONE

Whole TX buffer was transmitted.

enumerator UART_TX_ABORTED

Transmitting aborted due to timeout or uart_tx_abort call.

When flow control is enabled, there is a possibility that TX transfer won’t finish in the allotted time. Some data may have been transferred, information about it can be found in event data.

enumerator UART_RX_RDY

Received data is ready for processing.

This event is generated in the following cases:

  • When RX timeout occurred, and data was stored in provided buffer. This can happen multiple times in the same buffer.

  • When provided buffer is full.

  • After uart_rx_disable().

  • After stopping due to external event (UART_RX_STOPPED).

enumerator UART_RX_BUF_REQUEST

Driver requests next buffer for continuous reception.

This event is triggered when receiving has started for a new buffer, i.e. it’s time to provide a next buffer for a seamless switchover to it. For continuous reliable receiving, user should provide another RX buffer in response to this event, using uart_rx_buf_rsp function

If uart_rx_buf_rsp is not called before current buffer is filled up, receiving will stop.

enumerator UART_RX_BUF_RELEASED

Buffer is no longer used by UART driver.

enumerator UART_RX_DISABLED

RX has been disabled and can be reenabled.

This event is generated whenever receiver has been stopped, disabled or finished its operation and can be enabled again using uart_rx_enable

enumerator UART_RX_STOPPED

RX has stopped due to external event.

Reason is one of uart_rx_stop_reason.

Functions

static inline int uart_callback_set(const struct device *dev, uart_callback_t callback, void *user_data)

Set event handler function.

Since it is mandatory to set callback to use other asynchronous functions, it can be used to detect if the device supports asynchronous API. Remaining API does not have that detection.

Parameters:

  • dev – UART device instance.

  • callback – Event handler.

  • user_data – Data to pass to event handler function.

Return values:

  • 0 – If successful.

  • -ENOSYS – If not supported by the device.

  • -ENOTSUP – If API not enabled.

int uart_tx(const struct device *dev, const uint8_t *buf, size_t len, int32_t timeout)

Send given number of bytes from buffer through UART.

Function returns immediately and event handler, set using uart_callback_set, is called after transfer is finished.

Parameters:

  • dev – UART device instance.

  • buf – Pointer to transmit buffer.

  • len – Length of transmit buffer.

  • timeout – Timeout in microseconds. Valid only if flow control is enabled. SYS_FOREVER_US disables timeout.

Return values:

  • 0 – If successful.

  • -ENOTSUP – If API is not enabled.

  • -EBUSY – If There is already an ongoing transfer.

  • -errno – Other negative errno value in case of failure.

int uart_tx_u16(const struct device *dev, const uint16_t *buf, size_t len, int32_t timeout)

Send given number of datum from buffer through UART.

Function returns immediately and event handler, set using uart_callback_set, is called after transfer is finished.

Parameters:

  • dev – UART device instance.

  • buf – Pointer to wide data transmit buffer.

  • len – Length of wide data transmit buffer.

  • timeout – Timeout in milliseconds. Valid only if flow control is enabled. SYS_FOREVER_MS disables timeout.

Return values:

  • 0 – If successful.

  • -ENOTSUP – If API is not enabled.

  • -EBUSY – If there is already an ongoing transfer.

  • -errno – Other negative errno value in case of failure.

int uart_tx_abort(const struct device *dev)

Abort current TX transmission.

UART_TX_DONE event will be generated with amount of data sent.

Parameters:

  • dev – UART device instance.

Return values:

  • 0 – If successful.

  • -ENOTSUP – If API is not enabled.

  • -EFAULT – There is no active transmission.

  • -errno – Other negative errno value in case of failure.

int uart_rx_enable(const struct device *dev, uint8_t *buf, size_t len, int32_t timeout)

Start receiving data through UART.

Function sets given buffer as first buffer for receiving and returns immediately. After that event handler, set using uart_callback_set, is called with UART_RX_RDY or UART_RX_BUF_REQUEST events.

Parameters:

  • dev – UART device instance.

  • buf – Pointer to receive buffer.

  • len – Buffer length.

  • timeout – Inactivity period after receiving at least a byte which triggers UART_RX_RDY event. Given in microseconds. SYS_FOREVER_US disables timeout. See uart_event_type for details.

Return values:

  • 0 – If successful.

  • -ENOTSUP – If API is not enabled.

  • -EBUSY – RX already in progress.

  • -errno – Other negative errno value in case of failure.

int uart_rx_enable_u16(const struct device *dev, uint16_t *buf, size_t len, int32_t timeout)

Start receiving wide data through UART.

Function sets given buffer as first buffer for receiving and returns immediately. After that event handler, set using uart_callback_set, is called with UART_RX_RDY or UART_RX_BUF_REQUEST events.

Parameters:

  • dev – UART device instance.

  • buf – Pointer to wide data receive buffer.

  • len – Buffer length.

  • timeout – Inactivity period after receiving at least a byte which triggers UART_RX_RDY event. Given in milliseconds. SYS_FOREVER_MS disables timeout. See uart_event_type for details.

Return values:

  • 0 – If successful.

  • -ENOTSUP – If API is not enabled.

  • -EBUSY – RX already in progress.

  • -errno – Other negative errno value in case of failure.

static inline int uart_rx_buf_rsp(const struct device *dev, uint8_t *buf, size_t len)

Provide receive buffer in response to UART_RX_BUF_REQUEST event.

Provide pointer to RX buffer, which will be used when current buffer is filled.

Note

Providing buffer that is already in usage by driver leads to undefined behavior. Buffer can be reused when it has been released by driver.

Parameters:

  • dev – UART device instance.

  • buf – Pointer to receive buffer.

  • len – Buffer length.

Return values:

  • 0 – If successful.

  • -ENOTSUP – If API is not enabled.

  • -EBUSY – Next buffer already set.

  • -EACCES – Receiver is already disabled (function called too late?).

  • -errno – Other negative errno value in case of failure.

static inline int uart_rx_buf_rsp_u16(const struct device *dev, uint16_t *buf, size_t len)

Provide wide data receive buffer in response to UART_RX_BUF_REQUEST event.

Provide pointer to RX buffer, which will be used when current buffer is filled.

Note

Providing buffer that is already in usage by driver leads to undefined behavior. Buffer can be reused when it has been released by driver.

Parameters:

  • dev – UART device instance.

  • buf – Pointer to wide data receive buffer.

  • len – Buffer length.

Return values:

  • 0 – If successful.

  • -ENOTSUP – If API is not enabled

  • -EBUSY – Next buffer already set.

  • -EACCES – Receiver is already disabled (function called too late?).

  • -errno – Other negative errno value in case of failure.

int uart_rx_disable(const struct device *dev)

Disable RX.

UART_RX_BUF_RELEASED event will be generated for every buffer scheduled, after that UART_RX_DISABLED event will be generated. Additionally, if there is any pending received data, the UART_RX_RDY event for that data will be generated before the UART_RX_BUF_RELEASED events.

Parameters:

  • dev – UART device instance.

Return values:

  • 0 – If successful.

  • -ENOTSUP – If API is not enabled.

  • -EFAULT – There is no active reception.

  • -errno – Other negative errno value in case of failure.

struct uart_event_tx
#include <uart.h>

UART TX event data.

Public Members

const uint8_t *buf

Pointer to current buffer.

size_t len

Number of bytes sent.

struct uart_event_rx
#include <uart.h>

UART RX event data.

The data represented by the event is stored in rx.buf[rx.offset] to rx.buf[rx.offset+rx.len]. That is, the length is relative to the offset.

Public Members

uint8_t *buf

Pointer to current buffer.

size_t offset

Currently received data offset in bytes.

size_t len

Number of new bytes received.

struct uart_event_rx_buf
#include <uart.h>

UART RX buffer released event data.

Public Members

uint8_t *buf

Pointer to buffer that is no longer in use.

struct uart_event_rx_stop
#include <uart.h>

UART RX stopped data.

Public Members

enum uart_rx_stop_reason reason

Reason why receiving stopped.

struct uart_event_rx data

Last received data.

struct uart_event
#include <uart.h>

Structure containing information about current event.

Public Members

enum uart_event_type type

Type of event.

union uart_event_data
#include <uart.h>

Event data.

Public Members

struct uart_event_tx tx

UART_TX_DONE and UART_TX_ABORTED events data.

struct uart_event_rx rx

UART_RX_RDY event data.

struct uart_event_rx_buf rx_buf

UART_RX_BUF_RELEASED event data.

struct uart_event_rx_stop rx_stop

UART_RX_STOPPED event data.