GPIO Usage

The BM1684 chip contains 3 groups of GPIO controllers, each of which controls 32 GPIOs, which correspond to the Linux device nodes as follows:

GPIO Controller	Linux Device Node	GPIO Physical Number	GPIO Logical Number
#0	/sys/class/gpio/gpiochip480	0 to 31	480 to 511
#1	/sys/class/gpio/gpiochip448	32 to 63	448 to 479
#2	/sys/class/gpio/gpiochip416	64 to 95	416 to 447

For example, to operate GPIO6, you need:

1. Number conversion: The physical number is 6, the corresponding logical number is (480 + (6 - 0)) = 486, 0 represents the start of the GPIO physical number

2. Export the GPIO, run as root user:

   echo 486 >/sys/class/gpio/export
   

3. Operate GPIO, set to read input or output specified value:

   cd /sys/class/gpio/gpio486
   # set input mode
   echo in >direction
   cat value
   
   # set output mode
   echo out >direction
   # output low level
   echo 0 >value
   # output high level
   echo 1 >value
   

There are a few things to note:

• If the GPIO has been applied by other drivers, it cannot be exported successfully, and subsequent read and write operations cannot be performed.

• Involving the multiplexing of IO functions, if the function of the pin is already GPIO, the above method can be used; otherwise, the pinctrl state must be specified in the device tree.

Generally speaking, if you want to easily operate a GPIO in the user layer, you can add it as a GPIO-LED in the device tree. Please refer to linux-linaro-stable/arch/arm64/boot/dts/bitmain/bm1684_firefly.dtsi for details.