i2c.h File Reference

API Description

An i2c context represents a master on an i2c bus and that context can communicate to multiple i2c slaves by configuring the address. It is considered best practice to make sure the address is correct before doing any calls on i2c, in case another application or even thread changed the addres on that bus. Multiple instances of the same bus can exist.

    i2c = mraa_i2c_init(I2C_BUS);
    if (i2c == NULL) {
        fprintf(stderr, "Failed to initialize I2C\n");
        mraa_deinit();
        return EXIT_FAILURE;
    }

    /* set slave address */
    status = mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    /* set device gain */
    rx_tx_buf[0] = HMC5883L_CONF_REG_B;
    rx_tx_buf[1] = GA_1_3_REG;

    status = mraa_i2c_write(i2c, rx_tx_buf, 2);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    status = mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    /* set continuous mode */
    rx_tx_buf[0] = HMC5883L_MODE_REG;
    rx_tx_buf[1] = HMC5883L_CONT_MODE;

    status = mraa_i2c_write(i2c, rx_tx_buf, 2);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    while (flag) {
#if 0
        int i = 0;
        /*
         * alternative, equivalent method which helps to understand exactly what
         * the below does
         */
        mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
        for (i = 0; i < DATA_REG_SIZE; i++) {
            mraa_i2c_read_byte_data(i2c, HMC5883L_DATA_REG+i);
        }
#endif
        /* select data register to read */
        status = mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
        if (status != MRAA_SUCCESS) {
            goto err_exit;
        }

        status = mraa_i2c_write_byte(i2c, HMC5883L_DATA_REG);
        if (status != MRAA_SUCCESS) {
            goto err_exit;
        }

        /* do a incremental read from the chosen address */
        status = mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
        if (status != MRAA_SUCCESS) {
            goto err_exit;
        }

        /* this call behaves very similarly to the Wire receive() call */
        mraa_i2c_read(i2c, rx_tx_buf, DATA_REG_SIZE);

        x = (rx_tx_buf[HMC5883L_X_MSB_REG] << 8) | rx_tx_buf[HMC5883L_X_LSB_REG];
        z = (rx_tx_buf[HMC5883L_Z_MSB_REG] << 8) | rx_tx_buf[HMC5883L_Z_LSB_REG];
        y = (rx_tx_buf[HMC5883L_Y_MSB_REG] << 8) | rx_tx_buf[HMC5883L_Y_LSB_REG];

        /* scale and calculate direction */
        direction = atan2(y * SCALE_0_92_MG, x * SCALE_0_92_MG);

        /* check if the signs are reversed */
        if (direction < 0) {
            direction += 2 * M_PI;
        }

        fprintf(stdout, "Compass scaled data x : %f, y : %f, z : %f\n", x * SCALE_0_92_MG,
                y * SCALE_0_92_MG, z * SCALE_0_92_MG);
        fprintf(stdout, "Heading : %f\n", direction * 180 / M_PI);

        sleep(2);
    }

    /* stop i2c */
    mraa_i2c_stop(i2c);

Go to the source code of this file.

Functions
mraa_i2c_context	mraa_i2c_init (int bus)
mraa_i2c_context	mraa_i2c_init_raw (unsigned int bus)
mraa_result_t	mraa_i2c_frequency (mraa_i2c_context dev, mraa_i2c_mode_t mode)
int	mraa_i2c_read (mraa_i2c_context dev, uint8_t *data, int length)
int	mraa_i2c_read_byte (mraa_i2c_context dev)
int	mraa_i2c_read_byte_data (mraa_i2c_context dev, const uint8_t command)
int	mraa_i2c_read_word_data (mraa_i2c_context dev, const uint8_t command)
int	mraa_i2c_read_bytes_data (mraa_i2c_context dev, uint8_t command, uint8_t *data, int length)
mraa_result_t	mraa_i2c_write (mraa_i2c_context dev, const uint8_t *data, int length)
mraa_result_t	mraa_i2c_write_byte (mraa_i2c_context dev, const uint8_t data)
mraa_result_t	mraa_i2c_write_byte_data (mraa_i2c_context dev, const uint8_t data, const uint8_t command)
mraa_result_t	mraa_i2c_write_word_data (mraa_i2c_context dev, const uint16_t data, const uint8_t command)
mraa_result_t	mraa_i2c_address (mraa_i2c_context dev, uint8_t address)
mraa_result_t	mraa_i2c_stop (mraa_i2c_context dev)

Typedefs
typedef struct _i2c *	mraa_i2c_context

Function Documentation

mraa_i2c_context mraa_i2c_init

(

int

bus

)

Initialise i2c context, using board defintions

Parameters

bus	i2c bus to use

Returns

i2c context or NULL

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mraa_i2c_context mraa_i2c_init_raw

(

unsigned int

bus

)

Initialise i2c context, passing in the i2c bus to use.

Parameters

bus	The i2c bus to use i.e. /dev/i2c-2 would be "2"

Returns

i2c context or NULL

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mraa_result_t mraa_i2c_frequency	(	mraa_i2c_context	dev,
		mraa_i2c_mode_t	mode
	)

Sets the frequency of the i2c context. Most platforms do not support this.

Parameters

dev	The i2c context
mode	The bus mode

Returns

Result of operation

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int mraa_i2c_read	(	mraa_i2c_context	dev,
		uint8_t *	data,
		int	length
	)

Simple bulk read from an i2c context

Parameters

dev	The i2c context
data	pointer to the byte array to read data in to
length	max number of bytes to read

Returns

length of the read in bytes or -1

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int mraa_i2c_read_byte

(

mraa_i2c_context

dev

)

Simple read for a single byte from the i2c context

Parameters

dev	The i2c context

Returns

The result of the read or -1 if failed

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int mraa_i2c_read_byte_data	(	mraa_i2c_context	dev,
		const uint8_t	command
	)

Read a single byte from i2c context, from designated register

Parameters

dev	The i2c context
command	The register

Returns

The result of the read or -1 if failed

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int mraa_i2c_read_word_data	(	mraa_i2c_context	dev,
		const uint8_t	command
	)

Read a single word from i2c context, from designated register

Parameters

dev	The i2c context
command	The register

Returns

The result of the read or -1 if failed

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int mraa_i2c_read_bytes_data	(	mraa_i2c_context	dev,
		uint8_t	command,
		uint8_t *	data,
		int	length
	)

Bulk read from i2c context, starting from designated register

Parameters

dev	The i2c context
command	The register
data	pointer to the byte array to read data in to
length	max number of bytes to read

Returns

The length in bytes passed to the function or -1

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mraa_result_t mraa_i2c_write	(	mraa_i2c_context	dev,
		const uint8_t *	data,
		int	length
	)

Write length bytes to the bus, the first byte in the array is the command/register to write

Parameters

dev	The i2c context
data	pointer to the byte array to be written
length	the number of bytes to transmit

Returns

Result of operation

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mraa_result_t mraa_i2c_write_byte	(	mraa_i2c_context	dev,
		const uint8_t	data
	)

Write a single byte to an i2c context

Parameters

dev	The i2c context
data	The byte to write

Returns

Result of operation

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mraa_result_t mraa_i2c_write_byte_data	(	mraa_i2c_context	dev,
		const uint8_t	data,
		const uint8_t	command
	)

Write a single byte to an i2c context

Parameters

dev	The i2c context
data	The byte to write
command	The register

Returns

Result of operation

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mraa_result_t mraa_i2c_write_word_data	(	mraa_i2c_context	dev,
		const uint16_t	data,
		const uint8_t	command
	)

Write a single word to an i2c context

Parameters

dev	The i2c context
data	The word to write
command	The register

Returns

Result of operation

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mraa_result_t mraa_i2c_address	(	mraa_i2c_context	dev,
		uint8_t	address
	)

Sets the i2c slave address.

Parameters

dev	The i2c context
address	The address to set for the slave (7-bit address)

Returns

Result of operation

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mraa_result_t mraa_i2c_stop

(

mraa_i2c_context

dev

)

De-inits an mraa_i2c_context device

Parameters

dev	The i2c context

Returns

Result of operation

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Typedef Documentation

typedef struct _i2c* mraa_i2c_context

Opaque pointer definition to the internal struct _i2c

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