Saving SD Card file immediately upon Power Failure

Soumayjit,

this can be a real tricky business. The FatFs module included with the TI-RTOS kernel uses semaphores for reentrancy protection, which means that you can't make FatFs calls from within a Hwi, Swi, or even the NMI for that matter. On another note, with the NMI, you can't call SYS/BIOS APIs either because BIOS it can't guarantee reentrancy with an interrupt that it can't disable.

With FatFs, here is an app note that suggests how to minimize critical sections. Perhaps you need some sort of monitor task that periodically saves small chunks of data.

Hi Tom,

   Thanks for your opinion.

PART 1:

   I would like to ask, what if I disable NMI inside the NMIsr function (my NMI service function) by re-configuring the NMI pin as a normal GPIO & then try to return from the NMI & take a quick action. Or is it that, NMI can never return even if I set the NMI pin as a GPIO (may be bcoz some NMI INTERRUPT Flag will be set which can not be cleared)?

   Also, what if I don't use NMI feature at all & keep the NMI pin as a GPIO right from the beginning of code execution. In this case, I am planning to read the status of the GPIO pin (power fail detection pin) just before initiating a file write. If a power fail detection is asserted, then I will call fclose() instead of calling fwrite() & I will wait in an infinite loop. At the same time, from some other Task (high priority task) I will execute the following code.

while(1)
{
    Task_sleep(50); // 50 mSec
    if(power_fail_detect() == true && flag_file_write_in_progress == false)
    {
      if(global_file_handle != NULL)
      {
        fclose(global_file_handle);
      }
      while(1);
    }
}

   The variable, flag_file_write_in_progress will be set just before calling fwrite() & will be cleared after fwrite() returns.

Whatever works out, I'll try these options & post here the results.

PART 2:

   The link you provided, shows a function named f_sync(). Now, f_sync() function is part of elm-chan FatFs library, whereas I am using TI-RTOS FatFs library. My question is whether I can call both types of functions in the same Task? Somewhere (most probably in the TI-RTOS FatFs documentation/user guide) I found it is mentioned that mixing TI-RTOS FatFs & elm-chan FatFs may result into unpredictable behaviour of the FatFs & hence, its NOT recommended.

   Can I use f_sync() in my codes?

PART 3:

   Even if, I use elm-chan's FatFs function f_sync() & due to some power failure I am unable to call fclose() function, will the data still be written successfully to the file?

Thanks for your replies

Regards

Soumyajit