[Technical tips] How to test the SPI bus on NX8MM-35

This article will tell you how to test the SPI bus on the NX8MM-35 in Yocto Linux.
The SPI bus is an optional feature supported on ICOP's NX8MM-35, and it shares functionality with UART3 on the board.
In the tips below, we will provide the guide step by step.

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Tools you need:

1. NX8MM-35 (Find it here)
2. Yocto Linux 4.0:Image / Guide
3. USB to micro USB cable for restoring image.
4. SPI Testing file (Put it in a USB disk): link
5. A testing wire to test SPI bus self-transmitting.
   
6. Soldering iron for switching UART3 function to SPI bus.

Switching the UART3 to SPI bus on NX8MM-35.

On NX8MM-35, the UART3 and SPI bus can be switched by modifying the resistor on the board.
Please follow the image below and use the soldering iron to move the 0 ohm resistor to the correct location.

Test the SPI function in Yocto Linux.

 ./spidev_test -D /dev/spidev3.0 -v -p xxx 

In this case, we type ./spidev_test -D /dev/spidev3.0 -v -p SPITESTING, and if the test succeed, it will show the "SPITESTING" in the test result.

1. Plug testing wire to the J12 (SPI bus) on NX8MM-35.
2. Plug the USB disk with SPI testing application in the NX8MM-35 and turn it on; then open the terminal in Yocto Linux.
3. Mount the USB to Lunix and access the USB file.
4. Run below command in the USB file:

For the steps above, you could find all of the information in the image below:

Check the video:

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