spi_write()

Updated: May 06, 2022

The spi_write() function writes data to a specific device on the SPI bus. The prototype for this function is:

int spi_write( int fd,
               uint32_t device,
               void *buf,
               int len );

The arguments are:

fd
The file descriptor returned by spi_open().
device
The device ID with at most one of the following flags optionally ORed in:
  • SPI_DEV_LOCK
  • SPI_DEV_UNLOCK
buf
A pointer to the write buffer.
len
The length, in bytes, of the data to be written.

The function returns the number of bytes of data that it successfully wrote to the device. If an error occurred, the function returns -1 and sets errno:

EIO
The write to the device failed, or a hardware error occurred.
EINVAL
The device ID is invalid, or you're trying to unlock a device that isn't locked.
ENOMEM
Insufficient memory.
EPERM
The device is locked by another connection.

An SPI driver typically considers it to be an error if the number of bytes returned by this function isn't the same as the number of bytes it asked the function to write.