MX8 SPI

VAR-SOM-MX8X SPI

Overview

In this example we show how to configure and test SPI on VAR-SOM-MX8X. The SPI pins on external connector J16 will be used used to run SPI loopback test.

Kernel configuration

Verify that the i.MX LPSPI driver (CONFIG_SPI_FSL_LPSPI) is enabled in your kernel configuration:

• In menuconfig: Device Drivers -> SPI support -> <*> Freescale i.MX LPSPI controller
  

Verify that the User mode SPI driver (CONFIG_SPI_SPIDEV) is enabled in your kernel configuration:

• In menuconfig: Device Drivers -> SPI support -> <*> User mode SPI device driver support
  

Check spidev node

Check that spidev node exists and is enabled in arch/arm64/boot/dts/freescale/imx8qxp-var-som-common.dtsi.
GPIO1_0 will be used in this example to control SPI CS0.

&lpspi2 {
	#address-cells = <1>;
	#size-cells = <0>;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_lpspi2 &pinctrl_lpspi2_cs>;
	cs-gpios = <&gpio1 0 GPIO_ACTIVE_LOW>;
	status = "okay";

        spidev@0 {
		compatible = "spidev";
		spi-max-frequency = <12000000>;
		reg = <0>;
		status = "disabled";	
        };
};

Check configuration of SPI pins

&iomuxc {
	imx8qxp-var-som {
                ...
		pinctrl_lpspi2: lpspi2grp {
			fsl,pins = <
				SC_P_SPI2_SCK_ADMA_SPI2_SCK			0x0600004c
				SC_P_MCLK_IN0_ADMA_SPI2_SDI			0x0600004c
				SC_P_SPI2_SDO_ADMA_SPI2_SDO			0x0600004c
			>;
		};

		pinctrl_lpspi2_cs: lpspi2csgrp {
			fsl,pins = <
				SC_P_SPI2_CS0_LSIO_GPIO1_IO00			0x21
			>;
		};
                ...
	};
};

Recompile the kernel

Reompile the kernel and device tree (if any changes were made to DTS and kernel configuration) and update the SOM.

Compile SPI test application

There's an SPI test utility in the kernel source tree: tools/spi/spidev_test.c
To cross compile it, use the following command:

$ $CC ./tools/spi/spidev_test.c -o ./spidev_test

SPI External Connector

SPI is accessible on the following EVK pins:

• J16.2 - SCLK
• J16.4 - SS0
• J16.6 - MOSI
• J16.8 - MISO

Run SPI Test

Copy spidev_test binary to the SOM.
Loop MOSI and MISO by putting a jumper on J16.6 and J16.8

Run SPI test tool

# ./spidev_test -v -D /dev/spidev0.0 

The output of successful test should look like this:

spi mode: 0x20
bits per word: 8
max speed: 500000 Hz (500 KHz)
TX | FF FF FF FF FF FF 40 00 00 00 00 95 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF F0 0D  | ......@....�..................�.
RX | FF FF FF FF FF FF 40 00 00 00 00 95 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF F0 0D  | ......@....�..................�.