I am developing a slow rate (battery powered) data logger SW. I intend in a first time to store data in the local file system (flash memory). When I use fwrite() in a handler, if the main program does not end with a while(1) { }, fwrite fails (returns 0)... Why ?

If you show the code, we'll be able to pinpoint the issue, but in general, doing heavy work like fwrite or sometimes even printf in interrupt handlers is not a good idea. What you should do is store your data in some global variable and set a flag which is checked in main() and the actual work is done there.

Hi Igor, sorry for the delay. Here is a "demo" highlighting the problem ( USB cord used ). When I siwtched from local file system to USB stick in my project, I moved the writings in main(). Thanks for your support!

1. include "mbed.h"

int done = 0; boolean DigitalOut myled(LED1); LocalFileSystem local("local"); Create the local filesystem under the name "local" FILE *fp;

void InitRTC() { struct tm t; t.tm_sec = 0; 0-59 t.tm_min = 0; 0-59 t.tm_hour = 0; 0-23 t.tm_mday = 1; 1-31 t.tm_mon = 0; 0-11 t.tm_year = 70; year since 1900 set_time(mktime(&t)); Jan 1 00:00:00 1970, sothat timestamp starts at 0 LPC_RTC->CCR = 0; RTC is stopped until acquisition is started NB: time() restarts the RTC ! LPC_RTC->CIIR = 1; Select interrupts, 1=seconds LPC_RTC->ILR = 3; Clear the counter increment interrupt and the alarm interrupt flags }

extern "C" void RTC_IRQHandler() { if(done == 0) { if (LPC_RTC->MIN == 0) { myled = 1; fprintf(fp, "%i: Hello World!", LPC_RTC->SEC); wait(0.1); myled = 0; } else { fclose(fp); myled = 1; done = 1; } } LPC_RTC->ILR = 1; Clear the counter increment interrupt flag }

int main() { InitRTC(); fp = fopen("/local/out.txt", "w"); Open "out.txt" on the local file system for writing LPC_RTC->CCR = 1; Start RTC NVIC_EnableIRQ(RTC_IRQn); while(1){} COMMENT OUT THIS LINE AND THE WRITINGS FAIL ! }

Pierre, you need to use the code tags so the code is more legible.

I don't know if it is the issue, but if you are using fwrite, you should use "wb" in the fopen statement. fwrite is a binary file.

Second, have you tried putting a delay before it exits? Could it be that the interrupt isn't called before you exit?

-Doug

Without the While to stay in the Main program, you would immediately exit Main which would probably Close any files before you had a chance to do any writing.