i2c-bcm2711 driver example

The i2c-bcm2711 driver also implements the following functions:

int bcm2711_set_bus_speed(void *hdl, unsigned int speed, unsigned int *ospeed)

• Implements the set_bus_speed() function in the i2c_master_funcs_t structure.
• Specifies the bus speed. If an invalid bus speed is requested, this function should return failure and leave the bus speed unchanged.
• Arguments:
  • hdl — Handle returned from init().
  • speed — Bus speed. Units are implementation-defined.
  • ospeed — If not NULL, actual bus speed.
• Returns:
  • 0 — Success.
  • -1 — Failure.

int bcm2711_version_info(i2c_libversion_t *version)

• Implements the version_info() function in the i2c_master_funcs_t structure.
• Writes the library version information into passed version structure.
• Argument:
  • version — A pointer to the i2c_libversion_t structure to populate with version information:

    typedef struct {
        unsigned char major;
        unsigned char minor;
        unsigned char revision;
    } i2c_libversion_t;

• Returns:
  • 0 — Success.
  • -1 — Failure.

int bcm2711_driver_info(void *hdl, i2c_driver_info_t *info)

• Implements the driver_info() function in the i2c_master_funcs_t structure.
• Requests information about the driver.
• Arguments:
  • hdl — Handle returned from init().
  • info — A pointer to the i2c_driver_info_t structure to populate with version information:

    typedef struct {
        _Uint32t speed_mode; /* supported speeds: I2C_SPEED_* */
        _Uint32t addr_mode;  /* supported address fmts: I2C_ADDRFMT_* */
        _Uint32t verbosity;  /* Driver verbosity level */
        _Uint32t reserved;
    } i2c_driver_info_t;

• Returns:
  • 0 — Success.
  • -1 — Failure.

int bus_reset(void *hdl)

• Resets the I2C bus module.
• Returns:
  • 0 — Success.
  • -1 — Failure.

// 1) Reset the chip
rc = sn3218_reset();
if (rc != I2C_SUCCESS) {
    fprintf(stderr, "Error resetting SN3218.\n");
    return rc;
}

// 2) Exit shutdown (write 0x01 to REG_SHUTDOWN)
rc = sn3218_write_byte(REG_SHUTDOWN, 0x01);
if (rc != I2C_SUCCESS) {
    fprintf(stderr, "Error enabling SN3218 output.\n");
    return rc;
}

You can also utilize smbus_write_byte_data() to set the brightness of every LED to maximum (255):

// 3) Enable all 18 channels.
// Each LED control register (0x13, 0x14, 0x15) controls 6 channels (bits D5:D0).
// To enable each channel, write 0x3F (binary 00111111) to each register.
int rc;

// Enable all channels (registers 0x13, 0x14, 0x15)
for (int i = 0; i < 3; i++) {
    rc = smbus_write_byte_data(1, 0x54, 0x13 + i, 0x3F);
    if (rc != I2C_SUCCESS) {
        fprintf(stderr, "Error enabling SN3218 channels");
        return rc;
    }
    usleep(1000); // 1 ms delay between writes
}

// 4) Set all channels to maximum brightness (255)
uint8_t g_brightness[18]; // 18 channels
for (int i = 0; i < 18; i++) {
    g_brightness[i] = 255;
}

// Write brightness values to all 18 PWM registers (0x01-0x12)
for (int i = 0; i < 18; i++) {
    rc = smbus_write_byte_data(1, 0x54, 0x01 + i, g_brightness[i]);
    if (rc != I2C_SUCCESS) {
        fprintf(stderr, "Error writing brightness for channel %d.\n", i);
        return rc;
    }
    usleep(1000); // 1 ms delay between writes
}

// 5) Latch changes by writing to REG_UPDATE (0x16).
rc = smbus_write_byte_data(1, 0x54, 0x16, 0x00);
if (rc != I2C_SUCCESS) {
    fprintf(stderr, "Error updating SN3218.\n");
    return rc;
}

The following diagram shows how the i2c-bcm2711 driver communicates with a SN3218A RGB LED: