Power Fail and FAT FS file I/O

Narendra Kulkarni29

Intellectual 590 points

Hello,

H/w and S/w Configurations

H/W: TM4C12XNCZAD based custom board.

S/W: TI-RTOS - 2.14,

SYS/BIOS 6.42,

TI 5.2.5 Compiler,

xdctools_3_31_01_33

We are developing a TM4C12XNCZAD based custom board. It supports both USB and SD Card. The SD card is used for logging data. USB is basically used for transferring log data from SD Card. We are having power backup using a supercap (will support only for a minute). We are saving the required system data into an external EEPROM on power fail.

My questions are

When we are writing to SD card and power failure happens,

1. is it possible to write to SD Card with Super cap support

2. is it possible to safely exit from an write operation currently in progress (using file operation calls , fopen, fclose, fwrite) and to call fclose to safely close the file and umount SD card

Thanks in Advance

Narendra

over 10 years ago

0 janet over 10 years ago

TI__Mastermind 22760 points

Hi Narendra,
This is a software forum, and I think your questions should be posted on one of the hardware forums. I will request that this post be moved.
Best regards,
Janet

0 David Friedland over 10 years ago in reply to janet

TI__Mastermind 18320 points

Narenda,

I moved this thread over to the device forum in hopes that it will get a response there.

0 Amit Ashara over 10 years ago

TI__Guru**** 244440 points

Hello Narendra

Is the supercap meant for supplying the VDDS + VDDA rail?

Regards
Amit

0 Narendra Kulkarni29 over 10 years ago in reply to Amit Ashara

Intellectual 590 points

Hello Amit,

Yes.

Thanks
Narendra

0 f. m. over 10 years ago in reply to Narendra Kulkarni29

Guru 11940 points

IMHO there is hardly a way around actually measuring the capacitor state vs. energy consumption in most/all predictable cases. You might need to monitor the supercap voltage with an ADC channel, to estimate the remaining power.

And take into account that SD card writes sometimes involve a sector erase, causing it to take longer and consume more energy. The controller on the SD card usually hides this fact from you. And lastly, take aging of the supercap in account. "Normal" electrolytic caps can lose 50% of capacity over life time.

0 Amit Ashara over 10 years ago in reply to Narendra Kulkarni29

TI__Guru**** 244440 points

Hello Narendra

Note that the current consumption is high on the VDDS rail. As f.m. suggested it would be good to have an ADC channel to gauge the voltage. But before that you would need to first calculate the time for performing the operations required. Then plot the discharge time at full current consumption to arrive at the point on the ADC channel value to estimate the trip point for the save operation.

Regards
Amit

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Power Fail and FAT FS file I/O