Help. VEXcode Pro, write to SD card error

Programming Support VEXcode Pro V5 Text Tech Support
1

Hi forum, please help. I try to write log file to SD card for debugging. However, I got “memory permission error”.

I am aware that @jpearman had example using vex::brain::sdcard::savefile. I would like to learn if there is another way to do it.

Is it because vexos did not support stdio.

void usercontrol(void) {
  // User control code here, inside the loop
  FILE * usd_file_write;
  usd_file_write=fopen("log.txt", "w");
	fprintf(usd_file_write, "/* log file for debug */");
	fclose(usd_file_write);

  int timeOld=Brain.timer(timeUnits::msec);
  int timeNew ;
  int deltaTime;

  while (1) {
    timeNew=Brain.timer(timeUnits::msec);
    deltaTime=timeNew-timeOld;
    timeOld=Brain.timer(timeUnits::msec);

    FILE* usd_file_write = fopen("log.txt", "a");
    fprintf(usd_file_write, "wait(%d, msec)", deltaTime);
	  fclose(usd_file_write);  

    wait(20, msec); // Sleep the task for a short amount of time to
                    // prevent wasted resources.
  }
}
2

stdio if supported, you probably have an issue with the SD card. The memory permission error will come from using a NULL FILE pointer. You should always test return value of fopen.

void usercontrol(void) {
  // User control code here, inside the loop
  FILE * usd_file_write;
  usd_file_write=fopen("log.txt", "w");
  if( usd_file_write ) {
  	fprintf(usd_file_write, "/* log file for debug */\n");
	fclose(usd_file_write);
  }

  int timeOld=Brain.timer(timeUnits::msec);
  int timeNew ;
  int deltaTime;

  while (1) {
    timeNew=Brain.timer(timeUnits::msec);
    deltaTime=timeNew-timeOld;
    timeOld=Brain.timer(timeUnits::msec);

    FILE* usd_file_write = fopen("log.txt", "a");

    if( usd_file_write ) {
      fprintf(usd_file_write, "wait(%d, msec)\n", deltaTime);
      fclose(usd_file_write);  
    }

    wait(20, msec); // Sleep the task for a short amount of time to
                    // prevent wasted resources.
  }
}
2 Likes
3

Thank you for your help. Here is the updated code and I did see that fopen failed. I use the same SD card with other codes and VEXOS can write to this SD card. I do not think it is SD card issue. And the brain recognized the SD card

Is there anything else I need to change? printf( "sdcard exist %d", Brain.SDcard.isInserted()); shows 1.

void usercontrol(void) {
  // User control code here, inside the loop
  FILE * usd_file_write;
  usd_file_write=fopen("log.txt", "w");
	if( usd_file_write ) {
  	fprintf(usd_file_write, "/* log file for debug */\n");
	  fclose(usd_file_write);
    printf("success\n");
  } else printf("fail\n");
	

  printf( "sdcard exist %d", Brain.SDcard.isInserted());

  int timeOld=Brain.timer(timeUnits::msec);
  int timeNew ;
  int deltaTime;


  while (1) {
    timeNew=Brain.timer(timeUnits::msec);
    deltaTime=timeNew-timeOld;
    timeOld=Brain.timer(timeUnits::msec);

    FILE* usd_file_write = fopen("log.txt", "a");
    if( usd_file_write ) {
      fprintf(usd_file_write, "wait(%d, msec)\n", deltaTime);
      fclose(usd_file_write);  
      

    } 

    wait(20, msec); // Sleep the task for a short amount of time to
                    // prevent wasted resources.
  }
}
4

idk, I tried the code I posted and it works.

2 Likes
5

Thank you. It did work with another SD card (Samsung 128 GB PRO)!

The old card I used is Kingston 1GB and it works with std::ofstream ofs;, but not the code above.

6

As long as the SD card format is Fat32 it should not matter. Inside vexos, fopen, std::ofstream and sdcard. savefile all end up in exactly the same code.

2 Likes