#include <spidev.h>

Data Fields
__u64	tx_buf

__u64	rx_buf

__u32	len

__u32	speed_hz

__u16	delay_usecs

__u8	bits_per_word

__u8	cs_change

__u32	pad

Detailed Description

struct spi_ioc_transfer - describes a single SPI transfer : Holds pointer to userspace buffer with transmit data, or null. If no data is provided, zeroes are shifted out. : Holds pointer to userspace buffer for receive data, or null. : Length of tx and rx buffers, in bytes. : Temporary override of the device's bitrate. : Temporary override of the device's wordsize. : If nonzero, how long to delay after the last bit transfer before optionally deselecting the device before the next transfer. : True to deselect device before starting the next transfer.

This structure is mapped directly to the kernel spi_transfer structure; the fields have the same meanings, except of course that the pointers are in a different address space (and may be of different sizes in some cases, such as 32-bit i386 userspace over a 64-bit x86_64 kernel). Zero-initialize the structure, including currently unused fields, to accommodate potential future updates.

SPI_IOC_MESSAGE gives userspace the equivalent of kernel spi_sync(). Pass it an array of related transfers, they'll execute together. Each transfer may be half duplex (either direction) or full duplex.

struct spi_ioc_transfer mesg[4]; ... status = ioctl(fd, SPI_IOC_MESSAGE(4), mesg);

So for example one transfer might send a nine bit command (right aligned in a 16-bit word), the next could read a block of 8-bit data before terminating that command by temporarily deselecting the chip; the next could send a different nine bit command (re-selecting the chip), and the last transfer might write some register values.

Definition at line 85 of file spidev.h.