Difference between revisions of "SPI"
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== Linux configuration == | == Linux configuration == | ||
===APF27Dev with 2.6.29 kernel=== | ===APF27Dev with 2.6.29 kernel=== | ||
| − | SPI is used by some kernel drivers | + | SPI is used by some kernel drivers; when selecting them it will naturally activate the corresponding SPI bus. To use the SPI from user space you have first to be sure that the corresponding SPI bus is activated: |
| + | <pre class="host"> | ||
| + | $ make linux-menuconfig | ||
| + | </pre> | ||
<pre class="config"> | <pre class="config"> | ||
| Line 28: | Line 31: | ||
</pre> | </pre> | ||
| − | And | + | And user SPI device interface (spidev) option must be selected too (here as a module) : |
<pre class="config"> | <pre class="config"> | ||
Revision as of 17:55, 4 August 2017
This page will summarize the informations to use the SPI bus on APF boards.
Contents
Overview
SPI (Serial Peripheral Interface) is a 4-wire full-duplex serial bus. Wires used in SPI are :
- MOSI, Master Output Slave Input : send data to slave.
- MISO, Master Input Slave Output : receive data from slave.
- SCLK, : Serial Clock signal used to synchronise the transmission. (In imx27 (apf27) maximum frequency of SCLK is 22.167MHz in master mode and 16.625 in slave mode.
- SSx, Slave Select : used to select the slave for communication with master.
On APF27, the i.MX27 contains 3 SPI devices that can be configured in master (slave is not supported by linux). APF9328 (i.MXL) contains 2 SPI.
Linux configuration
APF27Dev with 2.6.29 kernel
SPI is used by some kernel drivers; when selecting them it will naturally activate the corresponding SPI bus. To use the SPI from user space you have first to be sure that the corresponding SPI bus is activated:
$ make linux-menuconfig
Device Drivers --->
[*] SPI support --->
...
<*> Freescale iMX SPI controller
[*] CSPI1
[*] CSPI2
[*] CSPI3
...
And user SPI device interface (spidev) option must be selected too (here as a module) :
Device Drivers --->
[*] SPI support --->
...
*** SPI Protocol Masters ***
<M> User mode SPI device driver support
...
By default, on APF27Dev, spidev device uses the bus number 2 (spi2.0) and PortB17 as chip select. To change this (for expert), the structure spi_board_info must be modified in platform file apf27-dev.c (in directory buildroot/output/build/linux-2.6.29.6/arch/arm/mach-mx2/) :
#ifdef CONFIG_SPI_SPIDEV
{
.modalias = "spidev",
.controller_data = &spidev_hw, /* for chip select */
.max_speed_hz = 8000000, /* 8MHz */
.bus_num = 1, /* SPI2 */
.mode = SPI_MODE_1,
.chip_select = 2,
.platform_data = &apf27_spidev_config,
},
#endif /* CONFIG_SPI_SPIDEV */
...
#ifdef CONFIG_SPI_SPIDEV
#define SPIDEV_CS (GPIO_PORTB | 17)
...
APF27Dev with 3.19+ kernels
- SPI3 bus, available on J8 connector, has been configured for spidev. You'll need an up-to-date apf27.dtb
- To change it you will have to edit arch/arm/boot/dts/imx27-apf27dev.dts in Linux sources and then recompile kernel (make linux) and update dtb from U-Boot (run update_dtb).
For more details on spidev usage, see kernel documentation.
Usage
When loaded this driver will create a /dev/spidev2.0 node to read/write on SPI bus from userspace.
# modprobe spidev
Linux user space C code
To write/read on SPI via spidev driver from your program, use ioctl as described in spidev documentation.
Linux kernel provides a test tool, to compile and use it:
$ mkdir spitest $ cd spitest $ cp buildroot/output/build/linux-x.x.x/Documentation/spi/spidev_test.c . $ ../buildroot/output/host/usr/bin/arm-linux-gcc -o spidev_test spidev_test.c $ scp spidev_test root@192.168.1.22:/root/
# ./spidev_test -D /dev/spidev2.0 -s 8000000
A simple library named as_spi has also been written for Armadeus Project.
