uart.h File Reference

API Description

UART is the Universal asynchronous receiver/transmitter interface to libmraa. It allows the exposure of UART pins on supported boards. With functionality to expand at a later date.

    /* initialize UART */
    uart = mraa_uart_init(UART);
    if (uart == NULL) {
        fprintf(stderr, "Failed to initialize UART\n");
        goto err_exit;
    }

    while (flag) {
        /* send data through UART */
        mraa_uart_write(uart, buffer, sizeof(buffer));

        sleep(1);
    }

    /* stop UART */
    mraa_uart_stop(uart);

Go to the source code of this file.

Functions
mraa_uart_context	mraa_uart_init (int uart)
mraa_uart_context	mraa_uart_init_raw (const char *path)
mraa_result_t	mraa_uart_flush (mraa_uart_context dev)
mraa_result_t	mraa_uart_sendbreak (mraa_uart_context dev, int duration)
mraa_result_t	mraa_uart_set_baudrate (mraa_uart_context dev, unsigned int baud)
mraa_result_t	mraa_uart_set_mode (mraa_uart_context dev, int bytesize, mraa_uart_parity_t parity, int stopbits)
mraa_result_t	mraa_uart_set_flowcontrol (mraa_uart_context dev, mraa_boolean_t xonxoff, mraa_boolean_t rtscts)
mraa_result_t	mraa_uart_set_timeout (mraa_uart_context dev, int read, int write, int interchar)
mraa_result_t	mraa_uart_set_non_blocking (mraa_uart_context dev, mraa_boolean_t nonblock)
const char *	mraa_uart_get_dev_path (mraa_uart_context dev)
mraa_result_t	mraa_uart_settings (int index, const char **devpath, const char **name, int *baudrate, int *databits, int *stopbits, mraa_uart_parity_t *parity, unsigned int *rtscts, unsigned int *xonxoff)
mraa_result_t	mraa_uart_stop (mraa_uart_context dev)
int	mraa_uart_read (mraa_uart_context dev, char *buf, size_t length)
int	mraa_uart_write (mraa_uart_context dev, const char *buf, size_t length)
mraa_boolean_t	mraa_uart_data_available (mraa_uart_context dev, unsigned int millis)

Typedefs
typedef struct _uart *	mraa_uart_context

Function Documentation

mraa_uart_context mraa_uart_init

(

int

uart

)

Initialise uart_context, uses board mapping

Parameters

uart	the index of the uart set to use

Returns

uart context or NULL

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mraa_uart_context mraa_uart_init_raw

(

const char *

path

)

Initialise a raw uart_context. No board setup.

Parameters

path	for example "/dev/ttyS0"

Returns

uart context or NULL

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mraa_result_t mraa_uart_flush

(

mraa_uart_context

dev

)

Flush the outbound data. Blocks until complete.

Parameters

dev	The UART context

Returns

Result of operation

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mraa_result_t mraa_uart_sendbreak	(	mraa_uart_context	dev,
		int	duration
	)

Send a break to the device. Blocks until complete.

Parameters

dev	The UART context
duration	When 0, send a break lasting at least 250 milliseconds, and not more than 500 milliseconds. When non zero, the break duration is implementation specific.

Returns

Result of operation

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mraa_result_t mraa_uart_set_baudrate	(	mraa_uart_context	dev,
		unsigned int	baud
	)

Set the baudrate. Takes an int and will attempt to decide what baudrate is to be used on the UART hardware.

Parameters

dev	The UART context
baud	unsigned int of baudrate i.e. 9600

Returns

Result of operation

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mraa_result_t mraa_uart_set_mode	(	mraa_uart_context	dev,
		int	bytesize,
		mraa_uart_parity_t	parity,
		int	stopbits
	)

Set the transfer mode For example setting the mode to 8N1 would be "mraa_uart_set_mode(dev, 8,MRAA_UART_PARITY_NONE , 1)"

Parameters

dev	The UART context
bytesize	data bits
parity	Parity bit setting
stopbits	stop bits

Returns

Result of operation

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mraa_result_t mraa_uart_set_flowcontrol	(	mraa_uart_context	dev,
		mraa_boolean_t	xonxoff,
		mraa_boolean_t	rtscts
	)

Set the flowcontrol

Parameters

dev	The UART context
xonxoff	XON/XOFF Software flow control.
rtscts	RTS/CTS out of band hardware flow control

Returns

Result of operation

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mraa_result_t mraa_uart_set_timeout	(	mraa_uart_context	dev,
		int	read,
		int	write,
		int	interchar
	)

Set the timeout for read and write operations <= 0 will disable that timeout

Parameters

dev	The UART context
read	read timeout
write	write timeout
interchar	inbetween char timeout

Returns

Result of operation

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mraa_result_t mraa_uart_set_non_blocking	(	mraa_uart_context	dev,
		mraa_boolean_t	nonblock
	)

Set the blocking state for write operations

Parameters

dev	The UART context
nonblock	new nonblocking state

Returns

Result of operation

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const char* mraa_uart_get_dev_path

(

mraa_uart_context

dev

)

Get Char pointer with tty device path within Linux For example. Could point to "/dev/ttyS0"

Parameters

dev	uart context

Returns

char pointer of device path

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mraa_result_t mraa_uart_settings	(	int	index,
		const char **	devpath,
		const char **	name,
		int *	baudrate,
		int *	databits,
		int *	stopbits,
		mraa_uart_parity_t *	parity,
		unsigned int *	rtscts,
		unsigned int *	xonxoff
	)

Get the current settings of an UART. This is an unintrusive function. Meaning it intends not to change anything, only read the values without disturbing.

All but the first index parameter are "outparameters". That means they can contain values on return. If any parameter is not interesting, a null pointer can be sent instead as a placeholder. The devpath parameter can be either in or out parameter. In case of a negative index, the UART is identified using *devpath instead. This functionality is intended for and needed by for instance USB serial adapters.

In case of a non-success return value, the outparameters are undefined.

Parameters

index	uart index to look up, if negative, *devpath will be used instead
devpath	points to the device path of the UART, eg: /dev/ttyS0
name	outparameter that on return will point to the name of the UART
baudrate	pointer to an integer to contain the current baudrate (0–4M)
databits	pointer to an integer to contain the number databits (5–8)
stopbits	pointer to an integer to contain the number stopbits (1–2)
parity	will contain the current parity mode
rtscts	will point to non-zero if CTS/RTS flow control is enabled, zero otherwise
xonxoff	will point to a non-zero value if xon/xoff flow control is enabled

Returns

result

mraa_result_t mraa_uart_stop

(

mraa_uart_context

dev

)

Destroy a mraa_uart_context

Parameters

dev	uart context

Returns

mraa_result_t

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int mraa_uart_read	(	mraa_uart_context	dev,
		char *	buf,
		size_t	length
	)

Read bytes from the device into a buffer

Parameters

dev	uart context
buf	buffer pointer
length	maximum size of buffer

Returns

the number of bytes read, or -1 if an error occurred

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int mraa_uart_write	(	mraa_uart_context	dev,
		const char *	buf,
		size_t	length
	)

Write bytes in buffer to a device

Parameters

dev	uart context
buf	buffer pointer
length	maximum size of buffer

Returns

the number of bytes written, or -1 if an error occurred

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mraa_boolean_t mraa_uart_data_available	(	mraa_uart_context	dev,
		unsigned int	millis
	)

Check to see if data is available on the device for reading

Parameters

dev	uart context
millis	number of milliseconds to wait, or 0 to return immediately

Returns

1 if there is data available to read, 0 otherwise

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Typedef Documentation

typedef struct _uart* mraa_uart_context

Mraa Uart Context

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