UM0851 datasheet(88/245 Pages) STMICROELECTRONICS

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Communication device drivers

UM0851

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Doc ID 16604 Rev 2

Figure 22.

SPI driver architecture

4.6.3

SPI framework in Linux

The Linux SPI Framework defines two types of SPI drivers in Linux (see Figure 22):

●

Controller drivers: these drivers configure SPI controllers. Their interface can be used

for configuring the controller and transfer data over the SPI bus. They may or may not

use DMA for data transfer with the slave device. The Linux SPI framework uses

controller drivers for all its SPI related operations. You can find them at

drivers/spi/spr_ssp_pl022*.

●

Protocol/Slave drivers: These drivers pass messages through the controller driver to

communicate with a slave device on the other side of a SPI link. They are present

above the SPI kernel framework and they provide interface to the user applications

present in the user space.

Currently two sample protocol drivers are present in the LSP drivers/spi folder.

●

EEPROM protocol driver: This driver uses the SPI framework to communicate with a

M25P40 EEPROM chip present on the SPEAr board. You can access it by opening,

reading and writing the following node:

sys/bus/spi/drivers/eeprom/spi3.1/m25

●

General char interface driver - spidev: This driver provides a char dev interface to

the SPI controller. To access it, use the following calls: Open(), Read(), Write() and

Ioctl().

Note:

For a new interface you have to write a new protocol driver. For information on using the SPI

framework, please see eeprom.c and spidev.c files in drivers/spi folder.

User applications

Hardware

Kernel space

User space

EEPROM protocol driver

SPIDEV protocol driver

Linux SPI framework

SPI controller driver

SSP controller (ARM Prime cell - PL 022)

SPI slave devicesSPI slave memory

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