Hello,

My simple application is toggle the CPU GPIO (GPIO control made by direct memory access using mmap of /dev/mem)
But somehow, the GPIO signal toggling is delayed. I monitor the GPIO with Oscilloscope and see that the signal is toggle a few second after the application toggle command.

Do you have any idea?

Regards,
stz

Processes in Linux/UNIX use priority/niceness to determine when they scheduled. It sounds like you're looking for "Real Time priority". Haven't dealt with this in Linux but have in UNIX. Found the following discussion of Real Time for Linux that may be of help to you:

http://www.linuxdevices.com/articles/AT4503827066.html

Hi,

I don’t need a real time performance. But I have to understand the delay reason for the following simple flow :
1)set GPIO to “1”
2) printf(“GPIO value == 1\r\n”)
3)sleep(20) - sleep for 20second
4)set GPIO to “0”
5) printf(“GPIO value == 0\r\n”)
6)sleep(20) - sleep for 20second
5)goto 1)

>> printf message is after GPIO setting !!!


Monitor result:

GPIO value == 1
After few seconds (~4 ) the signal is “1”
….here is the sleep delay
GPIO value == 0
After few seconds (~4 ) the signal is “0”
….here is the sleep delay

so why the GPIO signal is delayed after the printf message ?


Thanks,