Unable to write 0xFF to the eeprom on atmega328p.

[zignig]

Unable to write 0xFF to the eeprom on atmega32p.

I was attempting to save some configurations onto eeprom that loads on boot so I can keep a callibration.

https://github.com/zignig/steves_brain/blob/c84cc40a48b77447823c9748c828ccb39eae7bd4/joybox/joycontroller/src/joystick.rs#L98

Serializing with hubpack. I noticed that the negative numbers were not reloading correctly.

Overwriting with an 0xFF left the cell unchanged, so i16's were wrong.
After chasing through the hal and the I found the folowing code.

avr-hal/avr-hal-generic/src/eeprom.rs

Line 167 in d191b57

fn raw_write_byte(&mut self, address: u16, data: u8) {

when the byte is FF is does not appear to write correctly.

I took out the 'if' with a bare write

zignig@898ab15

and it worked for write but the erase function is borked.

I have tried this on other boards same result, so I think it's a bug.

I am running

• rustc 1.70.0-nightly (5e1d3299a 2023-03-31)
• promini
• ubuntu

Simplified example:

https://github.com/zignig/steves_brain/tree/main/scraps/eepromtest

There appears to be a bit overwrite strategy for eeprom , I am reading the AVR documentation to grok it.

[Rahix]

Paging @flyingyizi (ref #371).