How to recover calendar data after a reset

RE: How to recover calendar data after a reset

Paul Russell — Wed, 29 Oct 2014 17:15:33 GMT

You might need to adjust the RAM settings in the compiler to have some uninitialized RAM. Most compilers will zero the main block of variables, but addresses declared VOLATILE may not be cleared by the compiler. If volatile or similar keyword isn't supported, then check if you can adjust the RAM definitions so a few addresses at one end of RAM block are not in the initialized variable RAM block

may need to be absolute addresses\
add the CRC as Clem suggests (even a CRC8 from a table lookup is better than no CRC).

RE: How to recover calendar data after a reset

Tony.X — Wed, 29 Oct 2014 15:06:21 GMT

I agree on John's point of view of wearing flash too quick if keep saving it in a fix location. I haven't tried out what's RAM behavior after a reset but I think Clem's approach is worth trying.

RE: How to recover calendar data after a reset

Clem Taylor — Wed, 29 Oct 2014 02:40:03 GMT

Are the RAMs really zeroed on reset or is it just an issue that the behavior is undefined? If the ram doesn't really have a global reset you might be able to stick the current time and a crc in ram someplace and at least have a chance at recovering the current time. I've done this with DRAM (filled one page with the data we wanted to keep and a 64bit CRC, repeated over and over) the data could often survive for 10s of seconds with a complete power loss. DRAM != SRAM, but it might be something to try.

RE: How to recover calendar data after a reset

John — Tue, 28 Oct 2014 19:03:07 GMT

I would add a caveat to writing the time to flash: We don't know Tony's time accuracy requirement which would dictate how often he needs to save the time. If the time needs to be saved frequently, flash wear would be important. He may need to rotate the saved time through a large set of flash locations to prevent wearing out a single location. He'd also need a way to locate the latest time in flash after a reset. That might be simple if the time was something like a seconds since epoch counter.

RE: How to recover calendar data after a reset

Asbjørn — Tue, 28 Oct 2014 17:40:34 GMT

As @scytulip says, you would have to write the value of the clock/time to flash periodically. This would save it during a reset. RAM will be lost if a reset occurs.

RE: How to recover calendar data after a reset

scytulip — Tue, 28 Oct 2014 02:27:38 GMT

Save time info in Flash periodically?