From: <edwin.j....@gmail.com>
Reply-To: <beagleboard@googlegroups.com>
Date: Thursday, May 22, 2014 at 4:53 PM
To: <beagleboard@googlegroups.com>
Cc: <ej...@yahoo.com>
Subject: [beagleboard] Beaglebone Black: Reading GPIO at High Frequencies
>
> I would like to continuously read the status of an IO line on my Beaglebone
> black. The code I pasted below is a section of my software looking for rising
> and falling edges. Is there a way in Linux to read the status of that line
> without having to open and close the same file that is faster? The method I
> have below works, but only at really low frequencies.
>
> I am trying to read the IO approx. 15kHz.
Doing this from user space using the SYS filesystem is going to be slow. You
have two options in Linux:
1. Use mmap and read/write directly the GPIO registers
2. Use a kernel module or device driver to read/write the GPIO registers
However, even at 15KHz, the Linux kernel will be too slow because of
scheduling and interrupt latency. I suggest you try to do the high speed
stuff with the PRU and then interface with Linux for the high level data
manipulations.
Regards,
John
>
> Thanks
>
>
> while( buf[0]=='0' ) {
> memset(adc_drdy, 0, sizeof(adc_drdy) );
> if((j = fopen ( "/sys/class/gpio/gpio65/value", "r" )) == NULL) {
> //printSerial("Unable to read input file");
> }
> else {
> fgets(adc_drdy, sizeof(adc_drdy), j);
> strcpy(buf, adc_drdy);
> //fprintf(j, "%s", adc_drdy);
> fclose(j);
> }
> system("echo 0 > /sys/class/gpio/gpio61/value");
> printf("%c\n", buf[0]);
> //if(ADC_DRDY=='1') break;
> }
> while( buf[0]=='1' ) {
>
> memset(adc_drdy, 0, sizeof(adc_drdy) );
> if((j = fopen ( "/sys/class/gpio/gpio65/value", "r" )) == NULL) {
> //printSerial("Unable to read input file");
> }
> else {
> fgets(adc_drdy, sizeof(adc_drdy), j);
> strcpy(buf, adc_drdy);
> //fprintf(j, "%s", adc_drdy);
> fclose(j);
> }
> system("echo 1 > /sys/class/gpio/gpio61/value");
> printf("%c\n", buf[0]);
> //if(ADC_DRDY=='0') break;
> }
> --
> For more options, visit http://beagleboard.org/discuss
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