spi.h File Reference

API Description

This file defines the spi interface for libmraa. A Spi object in libmraa represents a spidev device. Linux spidev devices are created per spi bus and every chip select available on that bus has another spidev 'file'. A lot more information on spidev devices is available here.

    mraa_spi_context spi;
    spi = mraa_spi_init(0);
    unsigned int response = 0;
    printf("Hello, SPI initialised\n");
    uint8_t data[] = { 0x00, 100 };
    uint8_t* recv;
    while (1) {
        int i;
        for (i = 90; i < 130; i++) {
            data[1] = i;
            recv = mraa_spi_write_buf(spi, data, 2);
            printf("Writing -%i", i);
            printf("RECIVED-%i-%i\n", recv[0], recv[1]);
            usleep(100000);
        }
        for (i = 130; i > 90; i--) {
            data[1] = i;
            recv = mraa_spi_write_buf(spi, data, 2);
            printf("Writing -%i", i);
            printf("RECIVED-%i-%i\n", recv[0], recv[1]);
            usleep(100000);
        }
    }

Go to the source code of this file.

Functions
mraa_spi_context	mraa_spi_init (int bus)
mraa_spi_context	mraa_spi_init_raw (unsigned int bus, unsigned int cs)
mraa_result_t	mraa_spi_mode (mraa_spi_context dev, mraa_spi_mode_t mode)
mraa_result_t	mraa_spi_frequency (mraa_spi_context dev, int hz)
int	mraa_spi_write (mraa_spi_context dev, uint8_t data)
uint16_t	mraa_spi_write_word (mraa_spi_context dev, uint16_t data)
uint8_t *	mraa_spi_write_buf (mraa_spi_context dev, uint8_t *data, int length)
uint16_t *	mraa_spi_write_buf_word (mraa_spi_context dev, uint16_t *data, int length)
mraa_result_t	mraa_spi_transfer_buf (mraa_spi_context dev, uint8_t *data, uint8_t *rxbuf, int length)
mraa_result_t	mraa_spi_transfer_buf_word (mraa_spi_context dev, uint16_t *data, uint16_t *rxbuf, int length)
mraa_result_t	mraa_spi_lsbmode (mraa_spi_context dev, mraa_boolean_t lsb)
mraa_result_t	mraa_spi_bit_per_word (mraa_spi_context dev, unsigned int bits)
mraa_result_t	mraa_spi_stop (mraa_spi_context dev)

Typedefs
typedef struct _spi *	mraa_spi_context

Enumerations
enum	mraa_spi_mode_t { MRAA_SPI_MODE0 = 0, MRAA_SPI_MODE1 = 1, MRAA_SPI_MODE2 = 2, MRAA_SPI_MODE3 = 3 }

Function Documentation

mraa_spi_context mraa_spi_init

(

int

bus

)

Initialise SPI_context, uses board mapping. Sets the muxes

Parameters

bus	Bus to use, as listed in platform definition, normally 0

Returns

Spi context or NULL

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mraa_spi_context mraa_spi_init_raw	(	unsigned int	bus,
		unsigned int	cs
	)

Initialise SPI_context without any board configuration, selects a bus and a mux.

Parameters

bus	Bus to use as listed by spidev
cs	Chip select to use as listed in spidev

Returns

Spi context or NULL

mraa_result_t mraa_spi_mode	(	mraa_spi_context	dev,
		mraa_spi_mode_t	mode
	)

Set the SPI device mode. see spidev 0-3.

Parameters

dev	The Spi context
mode	The SPI mode, See Linux spidev

Returns

Result of operation

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mraa_result_t mraa_spi_frequency	(	mraa_spi_context	dev,
		int	hz
	)

Set the SPI device operating clock frequency.

Parameters

dev	the Spi context
hz	the frequency in hz

Returns

Result of operation

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int mraa_spi_write	(	mraa_spi_context	dev,
		uint8_t	data
	)

Write Single Byte to the SPI device.

Parameters

dev	The Spi context
data	Data to send

Returns

Data received on the miso line or -1 in case of error

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uint16_t mraa_spi_write_word	(	mraa_spi_context	dev,
		uint16_t	data
	)

Write Two Bytes to the SPI device.

Parameters

dev	The Spi context
data	Data to send

Returns

Data received on the miso line

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uint8_t* mraa_spi_write_buf	(	mraa_spi_context	dev,
		uint8_t *	data,
		int	length
	)

Write Buffer of bytes to the SPI device. The pointer return has to be free'd by the caller. It will return a NULL pointer in cases of error.

Parameters

dev	The Spi context
data	to send
length	elements within buffer, Max 4096

Returns

Data received on the miso line, same length as passed in

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uint16_t* mraa_spi_write_buf_word	(	mraa_spi_context	dev,
		uint16_t *	data,
		int	length
	)

Write Buffer of uint16 to the SPI device. The pointer return has to be free'd by the caller. It will return a NULL pointer in cases of error.

Parameters

dev	The Spi context
data	to send
length	elements (in bytes) within buffer, Max 4096

Returns

Data received on the miso line, same length as passed in

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mraa_result_t mraa_spi_transfer_buf	(	mraa_spi_context	dev,
		uint8_t *	data,
		uint8_t *	rxbuf,
		int	length
	)

Transfer Buffer of bytes to the SPI device. Both send and recv buffers are passed in

Parameters

dev	The Spi context
data	to send
rxbuf	buffer to recv data back, may be NULL
length	elements within buffer, Max 4096

Returns

Result of operation

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mraa_result_t mraa_spi_transfer_buf_word	(	mraa_spi_context	dev,
		uint16_t *	data,
		uint16_t *	rxbuf,
		int	length
	)

Transfer Buffer of uint16 to the SPI device. Both send and recv buffers are passed in

Parameters

dev	The Spi context
data	to send
rxbuf	buffer to recv data back, may be NULL
length	elements (in bytes) within buffer, Max 4096

Returns

Result of operation

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mraa_result_t mraa_spi_lsbmode	(	mraa_spi_context	dev,
		mraa_boolean_t	lsb
	)

Change the SPI lsb mode

Parameters

dev	The Spi context
lsb	Use least significant bit transmission. 0 for msbi

Returns

Result of operation

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mraa_result_t mraa_spi_bit_per_word	(	mraa_spi_context	dev,
		unsigned int	bits
	)

Set bits per mode on transaction, defaults at 8

Parameters

dev	The Spi context
bits	bits per word

Returns

Result of operation

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mraa_result_t mraa_spi_stop

(

mraa_spi_context

dev

)

De-inits an mraa_spi_context device

Parameters

dev	The Spi context

Returns

Result of operation

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Typedef Documentation

typedef struct _spi* mraa_spi_context

Opaque pointer definition to the internal struct _spi

Enumeration Type Documentation

enum mraa_spi_mode_t

MRAA SPI Modes

Enumerator
MRAA_SPI_MODE0	CPOL = 0, CPHA = 0, Clock idle low, data is clocked in on rising edge, output data (change) on falling edge
MRAA_SPI_MODE1	CPOL = 0, CPHA = 1, Clock idle low, data is clocked in on falling edge, output data (change) on rising edge
MRAA_SPI_MODE2	CPOL = 1, CPHA = 0, Clock idle low, data is clocked in on falling edge, output data (change) on rising edge
MRAA_SPI_MODE3	CPOL = 1, CPHA = 1, Clock idle low, data is clocked in on rising, edge output data (change) on falling edge

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