UART¶
Overview¶
API Reference¶
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group
uart_interface
UART Interface.
Typedefs
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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.
- Parameters
dev – UART device structure.
evt – Pointer to uart_event structure.
user_data – Pointer to data specified by user.
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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.
- Parameters
dev – UART device structure.
user_data – Arbitrary user data.
Enums
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enum
uart_line_ctrl
¶ Line control signals.
Values:
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enum
uart_event_type
¶ Types of events passed to callback in UART_ASYNC_API.
Receiving:
To start receiving, uart_rx_enable has to be called with first buffer
When receiving starts to current buffer, uart_event_type::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_event_type::UART_RX_RDY event will be generated and receiving will be stopped.
If some data was received and timeout occurred uart_event_type::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.
After buffer is filled uart_event_type::UART_RX_RDY will be generated, immediately followed by uart_event_type::UART_RX_BUF_RELEASED indicating that current buffer is no longer used.
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_event_type::UART_RX_DISABLED event is generated. After that whole process can be repeated.
Any time during reception uart_event_type::UART_RX_STOPPED event can occur. if there is any data received, uart_event_type::UART_RX_RDY event will be generated. It will be followed by uart_event_type::UART_RX_BUF_RELEASED event for every buffer currently passed to driver and finally by uart_event_type::UART_RX_DISABLED event.
Receiving can be disabled using uart_rx_disable, after calling that function, if there is any data received, uart_event_type::UART_RX_RDY event will be generated. uart_event_type::UART_RX_BUF_RELEASED event will be generated for every buffer currently passed to driver and finally uart_event_type::UART_RX_DISABLED event will occur.
Transmitting:
Transmitting starts by uart_tx function.
If whole buffer was transmitted uart_event_type::UART_TX_DONE is generated. If timeout occurred uart_event_type::UART_TX_ABORTED will be generated.
Transmitting can be aborted using uart_tx_abort, after calling that function uart_event_type::UART_TX_ABORTED event will be generated.
Values:
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enumerator
UART_TX_DONE
¶ Whole TX buffer was transmitted.
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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.
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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_event_type::UART_RX_STOPPED).
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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.
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enumerator
UART_RX_BUF_RELEASED
¶ Buffer is no longer used by UART driver.
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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
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enumerator
UART_RX_STOPPED
¶ RX has stopped due to external event.
Reason is one of uart_rx_stop_reason.
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enum
uart_rx_stop_reason
¶ Reception stop reasons.
Values that correspond to events or errors responsible for stopping receiving.
Values:
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enumerator
UART_ERROR_OVERRUN
= (1 << 0)¶ Overrun error.
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enumerator
UART_ERROR_PARITY
= (1 << 1)¶ Parity error.
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enumerator
UART_ERROR_FRAMING
= (1 << 2)¶ Framing error.
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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.
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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.
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enumerator
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enum
uart_config_parity
¶ Parity modes.
Values:
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enumerator
UART_CFG_PARITY_NONE
¶
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enumerator
UART_CFG_PARITY_ODD
¶
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enumerator
UART_CFG_PARITY_EVEN
¶
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enumerator
UART_CFG_PARITY_MARK
¶
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enumerator
UART_CFG_PARITY_SPACE
¶
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enumerator
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enum
uart_config_stop_bits
¶ Number of stop bits.
Values:
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enumerator
UART_CFG_STOP_BITS_0_5
¶
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enumerator
UART_CFG_STOP_BITS_1
¶
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enumerator
UART_CFG_STOP_BITS_1_5
¶
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enumerator
UART_CFG_STOP_BITS_2
¶
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enumerator
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enum
uart_config_data_bits
¶ Number of data bits.
Values:
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enumerator
UART_CFG_DATA_BITS_5
¶
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enumerator
UART_CFG_DATA_BITS_6
¶
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enumerator
UART_CFG_DATA_BITS_7
¶
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enumerator
UART_CFG_DATA_BITS_8
¶
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enumerator
UART_CFG_DATA_BITS_9
¶
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enumerator
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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:
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enumerator
UART_CFG_FLOW_CTRL_NONE
¶
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enumerator
UART_CFG_FLOW_CTRL_RTS_CTS
¶
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enumerator
UART_CFG_FLOW_CTRL_DTR_DSR
¶
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enumerator
Functions
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static inline int
uart_callback_set
(const struct device *dev, uart_callback_t callback, void *user_data)¶ Set event handler function.
- Parameters
dev – UART device structure.
callback – Event handler.
user_data – Data to pass to event handler function.
- Returns -ENOTSUP
If not supported.
- Returns 0
If successful, negative errno code otherwise.
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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 structure.
buf – Pointer to transmit buffer.
len – Length of transmit buffer.
timeout – Timeout in milliseconds. Valid only if flow control is enabled. SYS_FOREVER_MS disables timeout.
- Returns -ENOTSUP
If not supported.
- Returns -EBUSY
There is already an ongoing transfer.
- Returns 0
If successful, negative errno code otherwise.
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int
uart_tx_abort
(const struct device *dev)¶ Abort current TX transmission.
uart_event_type::UART_TX_DONE event will be generated with amount of data sent.
- Parameters
dev – UART device structure.
- Returns -ENOTSUP
If not supported.
- Returns -EFAULT
There is no active transmission.
- Returns 0
If successful, negative errno code otherwise.
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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_event_type::UART_RX_RDY or uart_event_type::UART_RX_BUF_REQUEST events.
- Parameters
dev – UART device structure.
buf – Pointer to receive buffer.
len – Buffer length.
timeout – Inactivity period after receiving at least a byte which triggers uart_event_type::UART_RX_RDY event. Given in milliseconds. SYS_FOREVER_MS disables timeout. See uart_event_type for details.
- Returns -ENOTSUP
If not supported.
- Returns -EBUSY
RX already in progress.
- Returns 0
If successful, negative errno code otherwise.
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static inline int
uart_rx_buf_rsp
(const struct device *dev, uint8_t *buf, size_t len)¶ Provide receive buffer in response to uart_event_type::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 structure.
buf – Pointer to receive buffer.
len – Buffer length.
- Returns -ENOTSUP
If not supported.
- Returns -EBUSY
Next buffer already set.
- Returns -EACCES
Receiver is already disabled (function called too late?).
- Returns 0
If successful, negative errno code otherwise.
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int
uart_rx_disable
(const struct device *dev)¶ Disable RX.
uart_event_type::UART_RX_BUF_RELEASED event will be generated for every buffer scheduled, after that uart_event_type::UART_RX_DISABLED event will be generated. Additionally, if there is any pending received data, the uart_event_type::UART_RX_RDY event for that data will be generated before the uart_event_type::UART_RX_BUF_RELEASED events.
- Parameters
dev – UART device structure.
- Returns -ENOTSUP
If not supported.
- Returns -EFAULT
There is no active reception.
- Returns 0
If successful, negative errno code otherwise.
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int
uart_err_check
(const struct device *dev)¶ Check whether an error was detected.
- Parameters
dev – UART device structure.
- Returns uart_rx_stop_reason
If error during receiving occurred.
- Returns 0
Otherwise.
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int
uart_poll_in
(const struct device *dev, unsigned char *p_char)¶ Poll the device for input.
- Parameters
dev – UART device structure.
p_char – Pointer to character.
- Returns 0
If a character arrived.
- Returns -1
If no character was available to read (i.e., the UART input buffer was empty).
- Returns -ENOTSUP
If the operation is not supported.
- Returns -EBUSY
If reception was enabled using uart_rx_enabled
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void
uart_poll_out
(const struct device *dev, unsigned char out_char)¶ Output a character in polled mode.
This routine checks if the transmitter is empty. When the transmitter is empty, it writes a character to the data register.
To send a character when hardware flow control is enabled, the handshake signal CTS must be asserted.
- Parameters
dev – UART device structure.
out_char – Character to send.
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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 structure.
cfg – UART configuration structure.
- Returns -ENOTSUP
If configuration is not supported by device. or driver does not support setting configuration in runtime.
- Returns 0
If successful, negative errno code otherwise.
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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 structure.
cfg – UART configuration structure.
- Returns -ENOTSUP
If driver does not support getting current configuration.
- Returns 0
If successful, negative errno code otherwise.
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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 structure.
tx_data – Data to transmit.
size – Number of bytes to send.
- Returns
Number of bytes sent.
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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).
Note that the calling context only applies to physical UARTs and no to the virtual ones found in USB CDC ACM code.
- Parameters
dev – UART device structure.
rx_data – Data container.
size – Container size.
- Returns
Number of bytes read.
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void
uart_irq_tx_enable
(const struct device *dev)¶ Enable TX interrupt in IER.
- Parameters
dev – UART device structure.
- Returns
N/A
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void
uart_irq_tx_disable
(const struct device *dev)¶ Disable TX interrupt in IER.
- Parameters
dev – UART device structure.
- Returns
N/A
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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 structure.
- Returns 1
If at least one char can be written to UART.
- Returns 0
Otherwise.
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void
uart_irq_rx_enable
(const struct device *dev)¶ Enable RX interrupt.
- Parameters
dev – UART device structure.
- Returns
N/A
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void
uart_irq_rx_disable
(const struct device *dev)¶ Disable RX interrupt.
- Parameters
dev – UART device structure.
- Returns
N/A
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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 structure.
- Returns 1
If nothing remains to be transmitted.
- Returns 0
Otherwise.
- Returns -ENOTSUP
if this function is not supported
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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 structure.
- Returns 1
If a received char is ready.
- Returns 0
Otherwise.
- Returns -ENOTSUP
if this function is not supported
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void
uart_irq_err_enable
(const struct device *dev)¶ Enable error interrupt.
- Parameters
dev – UART device structure.
- Returns
N/A
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void
uart_irq_err_disable
(const struct device *dev)¶ Disable error interrupt.
- Parameters
dev – UART device structure.
- Returns 1
If an IRQ is ready.
- Returns 0
Otherwise.
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int
uart_irq_is_pending
(const struct device *dev)¶ Check if any IRQs is pending.
- Parameters
dev – UART device structure.
- Returns 1
If an IRQ is pending.
- Returns 0
Otherwise.
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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 acknowledgement of interrupts, to ack any pending interrupts and likewise to cache the original value.
For devices with implicit acknowledgement, 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 structure.
- Returns 1
Always.
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static inline void
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 structure.
cb – Pointer to the callback function.
user_data – Data to pass to callback function.
- Returns
N/A
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static inline void
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 structure.
cb – Pointer to the callback function.
- Returns
N/A
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int
uart_line_ctrl_set
(const struct device *dev, uint32_t ctrl, uint32_t val)¶ Manipulate line control for UART.
- Parameters
dev – UART device structure.
ctrl – The line control to manipulate (see enum uart_line_ctrl).
val – Value to set to the line control.
- Returns 0
If successful.
- Returns failed
Otherwise.
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int
uart_line_ctrl_get
(const struct device *dev, uint32_t ctrl, uint32_t *val)¶ Retrieve line control for UART.
- Parameters
dev – UART device structure.
ctrl – The line control to retrieve (see enum uart_line_ctrl).
val – Pointer to variable where to store the line control value.
- Returns 0
If successful.
- Returns failed
Otherwise.
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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 structure.
cmd – Command to driver.
p – Parameter to the command.
- Returns 0
If successful.
- Returns failed
Otherwise.
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struct
uart_event_tx
¶ - #include <uart.h>
UART TX event data.
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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.
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struct
uart_event_rx_buf
¶ - #include <uart.h>
UART RX buffer released event data.
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struct
uart_event_rx_stop
¶ - #include <uart.h>
UART RX stopped data.
Public Members
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enum uart_rx_stop_reason
reason
¶ Reason why receiving stopped.
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struct uart_event_rx
data
¶ Last received data.
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enum uart_rx_stop_reason
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struct
uart_event
¶ - #include <uart.h>
Structure containing information about current event.
Public Members
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enum uart_event_type
type
¶ Type of event.
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union
uart_event_data
¶ - #include <uart.h>
Event data.
Public Members
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struct uart_event_tx
tx
¶ uart_event_type::UART_TX_DONE and uart_event_type::UART_TX_ABORTED events data.
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struct uart_event_rx
rx
¶ uart_event_type::UART_RX_RDY event data.
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struct uart_event_rx_buf
rx_buf
¶ uart_event_type::UART_RX_BUF_RELEASED event data.
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struct uart_event_rx_stop
rx_stop
¶ uart_event_type::UART_RX_STOPPED event data.
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struct uart_event_tx
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enum uart_event_type
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struct
uart_config
¶ - #include <uart.h>
UART controller configuration structure.
- param baudrate
Baudrate setting in bps
- param parity
Parity bit, use uart_config_parity
- param stop_bits
Stop bits, use uart_config_stop_bits
- param data_bits
Data bits, use uart_config_data_bits
- param flow_ctrl
Flow control setting, use uart_config_flow_control
-
struct
uart_device_config
¶ - #include <uart.h>
UART device configuration.
- param port
Base port number
- param base
Memory mapped base address
- param regs
Register address
- param sys_clk_freq
System clock frequency in Hz
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struct
uart_driver_api
¶ - #include <uart.h>
Driver API structure.
Public Members
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int (*
configure
)(const struct device *dev, const struct uart_config *cfg)¶ UART configuration functions
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int (*
fifo_fill
)(const struct device *dev, const uint8_t *tx_data, int len)¶ Interrupt driven FIFO fill function
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int (*
fifo_read
)(const struct device *dev, uint8_t *rx_data, const int size)¶ Interrupt driven FIFO read function
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void (*
irq_callback_set
)(const struct device *dev, uart_irq_callback_user_data_t cb, void *user_data)¶ Set the irq callback function
-
int (*
-
typedef void (*