Eeprom loosing its settings occasionally

[Yveaux]

On a self-assembled megadesk, which works just fine, I occasionally seem to loose the eeprom settings.
I regularly switch power supply of the desk.

Reading the Atmega's datasheet the most likely cause of eeprom corruption would be the execution of random code due to supply going down/coming up.

The BOD protection of the Atmega will keep the processor in reset when power levels are too low.
Looking at the fuses for megadesk, fusee is set to 0xFE, which disables the BOD.
As the Attiny is powered by 5V, enabling BOD at 4.3V typically (fusee set to 0xF4, fuseh set to 0xD4) would be able to prevent this kind of random code execution.

I will perform some tests with BOD enabled, but wondered if there is a good reason it is disabled by default ?

--
Update: First tests show normal operation; now to see if settings are preserved over time
Update2: Used it for a week, and eeprom loss did no longer occur

[gcormier]

Interesting! Let me know how things go.

Do you have any references for the datasheet where it mentions not using BOD can cause eeprom corruption?

[Yveaux]

Yes, https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-8495-8-bit-AVR-Microcontrollers-ATtiny441-ATtiny841_Datasheet.pdf pg 19/20:


Especially the second case may be an issue for Megadesk, causing rogue code to execute that may write to eeprom.

[gcormier]

Thanks! I've pushed some updates based on your recommendation :) Do you plan on building a companion?

[Yveaux]

Nice, but I think you missed efuse: 543a6fb#r144205644
See pg. 219 of the datasheet.

[Yveaux]

I didn't plan on building a companion, but I'd be happy to test it for you ;-)
Do you expect issues with it in combination with the BOD?

[gcormier]

No, but reach out to me on Tindie I'd love to support your efforts improving the project with the BOD observation.

[Yveaux]

After 2 weeks of testing I think it's safe to conclude that enabling BOD fixes the issue of eeprom loosing its settings.
Not a single loss occurred with BOD enabled, while before about every other day I had to re-store the desk levels.

[pfak]

This is fantastic news. This has been an issue for me for awhile. Is there a guide to updating? (I do not have a companion.)

[Yveaux]

AFAIK you need a programmer to do so.
This shows how to program the fuses for Megadesk: https://github.com/gcormier/megadesk/blob/master/DIY.md
And here you can find some more generic information on programming fuses: https://developerhelp.microchip.com/xwiki/bin/view/products/mcu-mpu/8-bit-avr/structure/fuses/