GPIO Pins Control - HummingBoard Pulse/Mate & i.MX8M Plus 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:

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# Export GPIO XX 
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XX=<GPIO-Linux-Number>
echo ${XX} > /sys/class/gpio/export

# Set GPIO pin Direction Output/Input
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# 1- Output -> 
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echo "out" > /sys/class/gpio/gpio${XX}/direction
# Set the output value
# High
echo 1 > /sys/class/gpio/gpio${XX}/value
# or LOW
echo 0 > /sys/class/gpio/gpio${XX}/value

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# 2- Input -> 
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echo "in" > /sys/class/gpio/gpio${XX}/direction
# Get the input value
cat /sys/class/gpio/gpio${XX}/value

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# Unexport GPIO XX
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echo ${XX} > /sys/class/gpio/unexport

(*) from the schematics you can find the name of the pin/pad (find the pad name of the imx8mp processor side) and from here pins-imx8mp.h can find the GPIO define name of the pin/pad with the GPIO option like (MX8MP_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: MX8MP_IOMUXC_SAI2_RXD0___GPIO4_IO23
GPIO Bank= 4

GPIO bit = 23

XX = ( 4 - 1) * 32 + 23 = 119

Attached here the MikroBus schematics:

Note: from here pins-imx8mp.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 use this repo to generate the kerenl - 

https://github.com/SolidRun/linux-stable/tree/lf-5.15-sr-imx8

• Here can find the imx8mp device  tree
  https://github.com/SolidRun/linux-stable/blob/linux-5.4.y-imx8/arch/arm64/boot/dts/freescale/imx8mp-hummingboard-pulse.dts