Example of GPIO read outside render()

rudeog

Hi,
I am trying to find an example of GPIO reading outside of render. I'd like to read some values and don't want it in the render loop, as I'd like to keep it for audio only. In other words something that doesn't require the BelaContext. I'm trying to use Gpio.h but am having difficulty figuring out how to construct the pin. I'm trying to use pins D0 and D1

Thanks.

giuliomoro

Gpio.h is meant to be used for pins that are not used by Bela. If you want to use one of those , you can read them from within render() and store their values in a global variable. If using other pins, you'll have to cross check:

the gem schematics to make sure those pins are not used on the board
the PB2 datasheet, page 38 and following to know the GPIO bank and number
grep for the address of each pin in the file /sys/kernel/debug/pinctrl/f4000.pinctrl-pinctrl-single/pins to make suer they are set to the correct mode

E.g.: pin P1.03 is free; poage 38 of the datasheet says it's GPIO1_51, so you can use gpio.open({1, 51}, ...). Its address is 0x000F4258, so

# grep -i F4258 /sys/kernel/debug/pinctrl/f4000.pinctrl-pinctrl-single/pins
pin 150 (PIN150) 51:601000.gpio f4258 00054000 pinctrl-single

the "mode" is the last digit of the last number: 00054000 means it's mode 0 . It needs to be mode 7 to be a GPIO. So this pin won't work as it is. Either you look for a different one or change the pinmuxing of this, either with a device tree overlay (see https://learn.bela.io/using-bela/technical-explainers/device-tree-overlays) or with a devmem2 hack (to be repeated at every boot):

# devmem2 0xf4258 w 0x00054007
/dev/mem opened.
Memory mapped at address 0xffff863e9000.
Read at address  0x000F4258 (0xffff863e9258): 0x00054000
Write at address 0x000F4258 (0xffff863e9258): 0x00054007, readback 0x00054007

now you can repeat the grep above and see that it has the correct mode (ends in "7"):

# root@bela:~/Bela# grep -i F4258 /sys/kernel/debug/pinctrl/f4000.pinctrl-pinctrl-single/pins
pin 150 (PIN150) 51:601000.gpio f4258 00054007 pinctrl-single

rudeog

Thanks Giulio that was the missing link. I will just stick to using the unused pins as they are more than enough for my needs.
I am now able to read pins using Gpio outside the render loop. Here is an example in case it helps anyone else:


#include <Bela.h>
#include <Gpio.h>


Gpio pinA, pinB;

#define PIN_A {1,21} // Digital pin 4
#define PIN_B {1,20} // Digital pin 5

void pinReadTask(void*) {
    if(pinA.open(PIN_A, Gpio::INPUT) != 0) {
		rt_printf("failed to open pin A for input\n");
		return;
	}
	if (pinB.open(PIN_B, Gpio::INPUT) !=0 ) {
		rt_printf("failed to open pin B for input\n");
		return;
	}
	
    while(!Bela_stopRequested()) {
        int pinAVal = pinA.read();
        int pinBVal = pinB.read();
        rt_printf("Pin A: %d, Pin B: %d\n", pinAVal, pinBVal);
        usleep(1000000); 
    }
    pinA.close();
    pinB.close();
}


bool setup(BelaContext *context, void *userData)
{
    Bela_runAuxiliaryTask(pinReadTask, 0);
	return true;
}

void render(BelaContext *context, void *userData)
{
	
}

void cleanup(BelaContext *context, void *userData)
{

}