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LED control on Pogoplug E02

Posted by BuckNaked 
LED control on Pogoplug E02
June 29, 2017 03:52PM
I'm chasing what I think should be an obvious issue, but I can't find it.

The host is a Pogoplug E02 running Debian jessie.

Logged into the system as root, the following two commands turn the green LED on and off as expected.

root@www:# echo "default-on" > "/sys/class/leds/status:green:health/trigger"
root@www:# echo "none" > "/sys/class/leds/status:green:health/trigger"

So here is a little program adapted from the one at https://github.com/suetanvil/ledflash/blob/master/ledflash.c, which to my mind should blink the green LED on and off a few times:

#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <syslog.h>
#include <string.h>
#include <sys/stat.h>

#   define FLASHFILE   "/sys/class/leds/status:green:health/trigger"
#   define ON          "default-on"
#   define OFF         "none"

void main() {
    FILE *ledfile;
    int status;

  ledfile = fopen(FLASHFILE, "w");
  if (ledfile == NULL) {
    printf("Unable to open '" FLASHFILE "' for write\n");
    printf("Error: %d (%s)\n", errno, strerror(errno));
    exit(0);
  }

  status = fputs("none", ledfile);
  sleep(1);
  status = fputs("default-on", ledfile);
  sleep(1);
  status = fputs("none", ledfile);
  sleep(1);
  status = fputs("default-on", ledfile);
  sleep(1);
  status = fputs("none", ledfile);
  sleep(1);
  status = fputs("default-on", ledfile);
  sleep(1);
  status = fputs("none", ledfile);
  sleep(1);
  status = fputs("default-on", ledfile);
  sleep(1);
  status = fputs("none", ledfile);
  sleep(1);
  status = fputs("default-on", ledfile);
  sleep(1);
  status = fputs("none", ledfile);

  exit(0);
}

The program's effect is exactly nothing. No error on the LED device file open, no blinking LED.

Does anyone see what the problem is here?
Re: LED control on Pogoplug E02
June 29, 2017 08:50PM
I don't know why it doesn't work and I'd be interested to know myself, but try this:
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <syslog.h>
#include <string.h>
#include <sys/stat.h>

#   define FLASHFILE   "/sys/class/leds/status:green:health/trigger"
#   define ON          "default-on",10
#   define OFF         "none",4

void main() {
    int status;
    int fn;

  fn = open(FLASHFILE,O_WRONLY);
  if(fn < 1){
    printf("Unable to open '" FLASHFILE "' for write\n");
    printf("Error: %d (%s)\n\n", errno, strerror(errno));
    exit(0);
  }

  status = write(fn,"none",4);
  sleep(1);
  status = write(fn,"default-on",10);
  sleep(1);
  status = write(fn,"none",4);
  sleep(1);
  status = write(fn,"default-on",10);
  sleep(1);
  status = write(fn,"none",4);
  sleep(1);
  status = write(fn,"default-on",10);
  sleep(1);
  status = write(fn,"none",4);
  sleep(1);
  status = write(fn,"default-on",10);
  sleep(1);
  status = write(fn,"none",4);
  sleep(1);
  status = write(fn,"default-on",10);
  sleep(1);
  status = write(fn,"none",4);
  close(fn);

  exit(0);
}
-JT
Re: LED control on Pogoplug E02
June 29, 2017 08:58PM
That works great. I'll adopt the code into the original program.

(Is it a disgraceful abuse of 70 years of hard work, technology and computer science to send Morse code through an LED on a Pogoplug?)
Re: LED control on Pogoplug E02
June 29, 2017 09:30PM
BuckNaked Wrote:
-------------------------------------------------------
> That works great. I'll adopt the code into
> the original program.
>
> (Is it a disgraceful abuse of 70 years of hard wor
> k, technology and computer science to send Morse c
> ode through an LED on a Pogoplug?)

Yes it is :)

You can try to echo "heartbeat" to the health trigger (instead of "default-on"). And then turn it back to "default-on" after a period of time.

-bodhi
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Re: LED control on Pogoplug E02
June 30, 2017 09:15AM
Expanding on renojim's solution above ... the problem occurs due to linux file buffering / caching.

It would be possible to get around it by calling fflush after every fputs, but the resulting code would be ugly and I believe that using write is a better solution anyway.
Re: LED control on Pogoplug E02
June 30, 2017 04:01PM
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