TP-LINK WR703n LED Blinker

wr703n-blink.c

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>

static const char* led_file = "/sys/devices/platform/leds-gpio/leds/tp-link:blue:system/brightness";
FILE *led_fh;

void cleanup(int);

int main() {
  uint8_t write_val[2];
  char err_msg[512];
  uint8_t toggle = 0;

  // open LED brightness device file for writing
  led_fh = fopen(led_file, "wb");
  if (led_fh == NULL) {
    sprintf(err_msg, "Cannot open LED device file %s", led_file);
    perror(err_msg);
    exit(1);
  }

  // catch interrupt signal
  struct sigaction int_handler = {
    .sa_flags = 0,
    .sa_handler = cleanup
  };
  sigemptyset(&int_handler.sa_mask);
  sigaction(SIGINT, &int_handler, NULL);

  // blink forever
  while (1) {
    strcpy(write_val, toggle ? "1" : "0");
    printf("Writing %s\n", write_val);
    rewind(led_fh);
    fprintf(led_fh, "%s\n", write_val);
    toggle = ~toggle;
    usleep(1000 * 40);  // sleep 40msec
  }
}

// called at interrupt
void cleanup(int s) {
  printf("Cleaning up...\n");
  fclose(led_fh);
  exit(0);
}