UART

Low-level UART peripheral driver.

This is a basic UART (Universal Asynchronous Receiver Transmitter) interface to allow platform independent access to the MCU’s serial communication abilities. This interface is intentionally designed to be as simple as possible, to allow for easy implementation and maximum portability. In RIOT we only use the common 8-N-1 format of the serial port (8 data bits, no parity bit, one stop bit).

The simple interface provides capabilities to initialize the serial communication module, which automatically enables for receiving data, as well as writing data to the UART port, which means transmitting data. The UART device and the corresponding pins need to be mapped in RIOT/boards/ * /include/periph_conf.h. Furthermore you need to select the baudrate for initialization which is typically {9600, 19200, 38400, 57600, 115200} baud. Additionally you should register a callback function that is executed in interrupt context when data is being received. The driver will then read the received data byte, call the registered callback function and pass the received data to it via its argument. The interface enforces the receiving to be implemented in an interrupt driven mode. Thus, you never know how many bytes are going to be received and might want to handle that in your specific callback function. The transmit function can be implemented in any way.

By default the UART_DEV(0) device of each board is initialized and mapped to STDIO in RIOT which is used for standard input/output functions like printf() or puts().

enum @150
UART_OK =  0
everything in order
UART_NODEV = -1
invalid UART device given
UART_NOBAUD = -2
given baudrate is not applicable
UART_INTERR = -3
all other internal errors
UART_NOMODE = -4
given mode is not applicable
unsigned int uart_t

Define default UART type identifier.

void(* uart_rx_cb_t()

Signature for receive interrupt callback.

Parameters

arg:context to the callback (optional)
data:the byte that was received

int uart_init(uart.h::uart_t uart, uint32_t baudrate, uart.h::uart_rx_cb_t rx_cb, void * arg)

Initialize a given UART device.

The UART device will be initialized with the following configuration:

  • 8 data bits
  • no parity
  • 1 stop bit
  • baudrate as given

If no callback parameter is given (rx_cb := NULL), the UART will be initialized in TX only mode.

Parameters

uart:UART device to initialize
baudrate:desired baudrate in baud/s
rx_cb:receive callback, executed in interrupt context once for every byte that is received (RX buffer filled), set to NULL for TX only mode
arg:optional context passed to the callback functions

Return values

  • UART_OK on success
  • UART_NODEV on invalid UART device
  • UART_NOBAUD on inapplicable baudrate
  • UART_INTERR on other errors
void uart_write(uart.h::uart_t uart, const uint8_t * data, msp430_types.h::size_t len)

Write data from the given buffer to the specified UART device.

This function is blocking, as it will only return after len bytes from the given buffer have been send. The way this data is send is up to the implementation: active waiting, interrupt driven, DMA, etc.

Parameters

uart:UART device to use for transmission
data:data buffer to send
len:number of bytes to send

void uart_poweron(uart.h::uart_t uart)

Power on the given UART device.

Parameters

uart:the UART device to power on

void uart_poweroff(uart.h::uart_t uart)

Power off the given UART device.

Parameters

uart:the UART device to power off

UART_UNDEF

Default UART undefined value. 

1
(UINT_MAX)
UART_DEV( x)

Default UART device access macro. 

1
(x)
struct uart_isr_ctx_t

Interrupt context for a UART device.

uart.h::uart_rx_cb_t rx_cb

data received interrupt callback

void * arg

argument to both callback routines