Saving Information in Flash-Memory without Erasing Cycle

[Andreas Fecht]

Hello,

I want to realize a startup-counter in a STM32L0xxx MCU.

This means a counter which counts how often the MCU is doing a power fail and restart for the whole life.

I want to save the actual counter-value in the flash memory.

But I don't want to kill the flash-memory-cells with more than 10k write an erase-cycles.

To solve this I want to save the counter-value without erasing-cycles:

Is it possible to write to a flash-cell more than one time without an erase cycle if I only want to *set* the bits? I know it is not possible to clear a bit.

A flash page has a capacity of 128Bytes. If I use every single bit for a counter-step, I can save 128x8=1024 counter-steps without an erase-cycle.

I've tested this, but I get some strange effects.

Is there a reason for this effects?

Maybe multi-level-flash-cells or ECC-correction?

Best regards

Andreas Fecht

[S.Ma]

What kind of strange effect?

[Andreas Fecht]

The following happens:

At an erased page all bits are cleared to 0.

My CPU (STM32L051) supports only a 32-Bit Flash HAL writing method (FLASH_TYPEPROGRAM_WORD).

For example:

Start at a flash adress with value 0x00000000

first set to 0x000000FF -> works

second set to 0x0000FFFF -> works

third set to 0x00FFFFFF -> works

at the next step I want to set it to 0xFFFFFFFF

and I get 0xBFFFFFFF back

Best regards

Andreas

[Tesla DeLorean]

Journal a write of words over a whole sector, pick the largest one, and increment that putting it in the next cell. Erase when you fill the whole sector, writing the old count at the front.

[Tesla DeLorean]

Not multi-level, but the flash lines are quite wide and 32-bits have additional bits of ECC/Hamming, which is why changing the word breaks things.

I don't see them mention it, but I'd assume at least 4-bits, so 32-bit stored as 36-bit. Sure you could extract specifics from an FAE.

https://www.st.com/content/ccc/resource/sales_and_marketing/promotional_material/brochure/6c/48/c0/f1/bb/35/4a/b4/brstm32ulp.pdf/files/brstm32ulp.pdf/jcr:content/translations/en.brstm32ulp.pdf

[waclawek.jan]

JW

[Andreas Fecht]

Thank You,

I think this helps me for my next Project.

I'm searching also for such a counter if a MCU has no internal EEPROM

Best regards

Andreas

[waclawek.jan]

> I'm searching also for such a counter if a MCU has no internal EEPROM

If you're talking about a different mcu, then you have to read the relevant chapters in that mcu's datasheet and reference manual. There's no universal answer to FLASH-related questions.

JW

[turboscrew]

"Is it possible to write to a flash-cell more than one time without an erase cycle if I only want to *set* the bits? I know it is not possible to clear a bit."

Isn't it the other way around? Usually erasing sets all bits? And you program the zeroes?

[Andreas Fecht]

This depends on the CPU-type.

This L0-series set all erased bits to 0.

I also use A L4-Type which set all erased Bits to 1.

Best regards

Andreas