I2CMaster_WriteThenRead Function

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Header: #include <applibs/i2c.h>

Performs a combined write-then-read operation on an I2C master interface. The operation appears as a single bus transaction with the following steps:

  1. start condition
  2. write
  3. repeated start condition
  4. read
  5. stop condition
ssize_t I2CMaster_WriteThenRead(int fd, I2C_DeviceAddress address, const uint8_t *writeData, size_t lenWriteData, uint8_t *readData, size_t lenReadData);

Parameters

  • fd The file descriptor for the I2C master interface.

  • address The address of the target I2C device for this operation.

  • writeData The data to transmit to the targeted device.

  • lenWriteData The byte length of the data to transmit.

  • readData The output buffer that receives data from the target device. This buffer must contain sufficient space to receive lenReadData bytes.

  • lenReadData The byte length of the data to receive.

Errors

Returns -1 if an error is encountered and sets errno to the error value.

  • EBUSY: the interface is busy or the I2C line is being held low.

  • ENXIO: the operation did not receive an ACK from the subordinate device.

  • ETIMEDOUT: the operation timed out before completing; you can use the I2CMaster_SetTimeout function to adjust the timeout duration.

Any other errno may also be specified; such errors aren't deterministic and the same behavior might not be retained through system updates.

Return value

Returns the combined number of bytes successfully written and read, or -1 for failure, in which case errno is set to the error value. A partial result, including a transfer of 0 bytes, is considered a success.

Application manifest requirements

To access an I2c interface, your application must identify it in the I2cMaster field of the application manifest.