GPIO Pins Control - HummingBoard Ripple/Pulse & i.MX8M Mini SOM

To control on the GPIO pins:

• The external GPIOs are available under the /sys/class/gpio folder in Linux.
• To control on the GPIO pins you need to calculate the GPIO number XX (*) and run the commands below:

# Export GPIO XX
echo XX > /sys/class/gpio/export

# Set GPIO pin Direction
echo "out" > /sys/class/gpio/gpioXX/direction
or
echo "in" > /sys/class/gpio/gpioXX/direction

# Set the value of an output pin
echo 1 > /sys/class/gpio/gpioXX/value
or
echo 0 > /sys/class/gpio/gpioXX/value

# Get the value of an input pin
cat > /sys/class/gpio/gpioXX/value

# Unexport GPIO XX
echo XX > /sys/class/gpio/unexport

(*) from the schematics you can find the name of the pin/pad (find the pad name of the imx8mm processor side) and from here pins-imx8mm.h can find the GPIO define name of the pin/pad with the GPIO option like (MX8MM_IOMUXC_SAI2_RXD0_GPIO4_IO23), then you can calculate the GPIO number XX

XX = linux gpio number = (gpio_bank - 1) * 32 + gpio_bit

Example: to calculate the GPIO number of mikroBus J8 [pin 2] Pad Name: SAI2_RXD

Pin Define: MX8MM_IOMUXC_SAI2_RXD0_GPIO4_IO23 GPIO Bank= 4

GPIO bit = 23

XX = ( 4 - 1) * 32 + 23 = 119

Attached here the MikroBus schematics:

MikroBus Pin	Pad Name (SOM side)	GPIO name	Linux GPIO number
J8 [pin 2]	SAI2_RXD	GPIO4_IO23	119
J8 [pin 3]	ECSPI2_SS0	GPIO5_IO13	141
J8 [pin 4]	ECSPI2_SCLK	GPIO5_IO10	138
J8 [pin 5]	ECSPI2_MISO	GPIO5_IO12	140
J8 [pin 6]	ECSPI2_MOSI	GPIO5_IO11	139
J10 [pin 1]	UART3_CTS -> UART3_RXD	GPIO5_IO26	154
J10 [pin 2]	UART3_RTS -> UART3_TXD	GPIO5_IO27	155
J10 [pin 3]	UART3_RXD -> UART1_RXD	GPIO5_IO22	150
J10 [pin 4]	UART3_TXD -> UART1_TXD	GPIO5_IO23	151
J10 [pin 5]	I2C3_SCL	GPIO5_IO18	146
J10 [pin 6]	I2C3_SDA	GPIO5_IO19	147

Note: from here pins-imx8mm.h can find the all supported functions of the pin (IOMUX options), from the Define names of same PAD name for example, this pad ECSPI2_SS0 can support 5 functions (UART RTC, UART CTS, SPI SS, GPIO, TPSMP_HDATA)

Define format MX8MM_IOMUX (for more information can see NXP documentations)

To use the SPI of the MikroBus you need to configure the SPI signals in the device tree & generate new Linux kernel + device tree

• You can this repo to generate the kerenl -

https://github.com/SolidRun/linux-stable/tree/linux-5.4.y-imx8

• Here can find the imx8mm device

https://github.com/SolidRun/linux-stable/blob/linux-5.4.y-imx8/arch/arm64/boot/dts/freescale/imx8mm-hummingboard-pulse.dts

You can see an example here - https://community.nxp.com/t5/i-MX-Processors/Problem-with-jedec-spi-nor-on-IMX8M-Mini-EVK/m-p/963020