BeagleBone Black and GPIO lines when using the Debian kernel

[chombourger]

We could switch to the Debian kernel for the BeagleBone Black with #195
Most device drivers appear to work fine.

GPIO lines however appear to be exposed differently.

I had the signal line of my 5V relay connected to GPIO_20 (P9)
That line appears to be already ON when the board is booted and toggling of the GPIO does not seem to work

[vj-kumar]

Maybe the GPIO is used differently in that kernel version? A dump of the dtb could give an idea. Or better if we find the original dts.

[vj-kumar]

@chombourger I see that the direction is by default input and value is high. Once I set the direction to out I do get value as 0 by default.

[chombourger]

good catch: power/gpio does not seem to change the direction to output

[vj-kumar]

The default value of high might be due to the internal pull-up resistor. Maybe pin configuration is done in such a way that it is pull-up by default.

[vj-kumar]

So, the input comes with pull-up(Value 1)

[vj-kumar]

It does set the direction in probe.

mtda/mtda/power/gpio.py

Line 51 in 016ae3d

f = open("/sys/class/gpio/gpio%d/direction" % pin, "w")

[vj-kumar]

Its number 28. Just verified with a multi meter. I am able to toggle it.

P9_12 is GPIO_60 (number 28 for gpio export)

Ref: https://beagleboard.org/static/images/cape-headers.png

root@mtda:/sys/class/gpio/gpio28# gpioinfo | grep P9_12
        line  28:      "P9_12"      "sysfs"  output  active-high [used]
root@mtda:/sys/class/gpio/gpio28# 

root@mtda:/sys/class/gpio/gpio28# cat direction 
in
root@mtda:/sys/class/gpio/gpio28# echo out > direction
root@mtda:/sys/class/gpio/gpio28# cat direction 
out
root@mtda:/sys/class/gpio/gpio28# cat value 
0
root@mtda:/sys/class/gpio/gpio28# echo 1 > value 
root@mtda:/sys/class/gpio/gpio28# cat value 
1

[vj-kumar]

root@mtda:/sys/class/gpio/gpio28# dpkg -l | grep linux-image
ii  linux-image-5.15.0-0.bpo.2-armmp     5.15.5-2~bpo11+1               armhf        Linux 5.15 for ARMv7 multiplatform compatible SoCs
ii  linux-image-armmp                    5.15.5-2~bpo11+1               armhf        Linux for ARMv7 multiplatform compatible SoCs (meta-package)
root@mtda:/sys/class/gpio/gpio28# uname -a
Linux mtda 5.15.0-0.bpo.2-armmp #1 SMP Debian 5.15.5-2~bpo11+1 (2022-01-02) armv7l GNU/Linux

[vj-kumar]

Note to self: VDD_5V on P9_5 / P9_6 is only available when external power supply is connected.

[chombourger]

Its number 28. Just verified with a multi meter. I am able to toggle it.

P9_12 is GPIO_60 (number 28 for gpio export)

Ref: https://beagleboard.org/static/images/cape-headers.png

root@mtda:/sys/class/gpio/gpio28# gpioinfo | grep P9_12
        line  28:      "P9_12"      "sysfs"  output  active-high [used]
root@mtda:/sys/class/gpio/gpio28# 

root@mtda:/sys/class/gpio/gpio28# cat direction 
in
root@mtda:/sys/class/gpio/gpio28# echo out > direction
root@mtda:/sys/class/gpio/gpio28# cat direction 
out
root@mtda:/sys/class/gpio/gpio28# cat value 
0
root@mtda:/sys/class/gpio/gpio28# echo 1 > value 
root@mtda:/sys/class/gpio/gpio28# cat value 
1

checked on my side and all is good with gpio28
thanks for the help!