How to set a GPIO to generate a square wave

Autonomous Machines Jetson & Embedded Systems Jetson TX2
1

Hello,
Recently，I have a project which used the Jetson connection with a microcontroller.And then I need a square wave,can we make some chaneged in dtb file to set a GPIO to generate a square wave?

2

hello qinyyuu,

may I have your confirmation about what’s the use-case that need a square wave.
I think you should be able to modify the linux kernel to program the GPIO high/low period to generate a square wave.
below general functions should be helpful.

sources/kernel/kernel-4.4/arch/arm/include/asm/gpio.h

#define gpio_get_value  __gpio_get_value
#define gpio_set_value  __gpio_set_value
3

Hello JerryChang,

I need a 1 MHz square wave as a signal source to monitor whether the system is running normally. Can you modify the implementation through the device tree? Is the kernel modified in a device-driver or other way?

4

hello qinyyuu,

I didn’t have experience to generate a square wave before,
you could try to modify the device driver and have implementation to program the GPIO high/low period to generate a square wave.
thanks

5

FYI, device tree can set up the GPIO to make it an output and be sure it is ready for a driver owned by you, but the device tree itself is not a timer (the device tree isn’t even a driver…it’s more or less a configuration the drivers read to match generic concepts to how a specific hardware configures to match the concept). Once the device tree reserves that GPIO for you to use you’ll still need to write a kernel driver capable of switching between 1 and 0 at the correct rate.

6

If you want to do a square wave, just set up a timer (e.g. 10ms) to set the GPIO output
(psuedocode)

Timer_task10ms //Thread function
{
    while (timer_task)
    {

    	if (current_gpio_state == 0)
    	{
    		gpioSetValue(j21_pin18, 1);
    	}
    	else if (current_gpio_state == 1)
    	{
    		gpioSetValue(j21_pin18, 0);
    	}
    	else
    	{
    		// Leave alone this time
    	}
    }    
}