ESP32 Forum

I have a 64 bit value I need to write to flash every 15 minutes and I need to do this over a 15 year product lifetime. This value will never be zero or all FFs.

What is the best way to wear level?

My plan is to use the spi flash api, erase a block (say 64k) write sequentially for 1000 writes, then erase and repeat. Which should give me (with a nominal 100,000 write cycle lifetime) 100,000,000 writes (which at 15 minutes gives me like a 3000 year lifetime).

Is this a valid approach or am I missing something ?

That is a valid approach.

Also depends if you want to know the beginning and end of the circlebuffer. You may need to start each block with a few flags to indicate where you are in the buffer.

Either that, or assume that the 'least full' block is the last one.

Although not likely to happen, but what if all blocks are completely full? What is the oldest one that should be discarded? Besides, you may want to store a read pointer to indicate if the logentry has been submitted to a server of some kind. I assume you want to copy this log to some database through a wifi connection? I didn't search, but doens't the ESP-IDF contain a NVS logging system? If not, I wouln't be supprised if you can find something that does this for you online.

Just an idea:
- A block is 4k
- An entry is 8bytes
- A block starts with a header containing a pointer to the next block. This would allow you to determine the first and last block. By only reading these pointers in the header.
- The header contains 2 bits for each entry stating whether the entry is empty and if its written to the server.
11 = Empty
01 = Written not read
00 = Written and read

Block: (4096 bytes per block)
- Header (128 bytes)
- List of entries (3968 bytes)

Block header
- Pointer = 2 bytes
- Entry status bits = 124 bytes (allows for 496 entries)
- 2 bytes unused.

Block list of entries
- 3968 / 8 = 496 entries

Yes this has some overhead, because of the status bits.
- The written bit isn't nessesary, you could simply search for the next entry containing only 0xFF. Altough an entry with only 0xFF wouldn't be possible.
- The read bit can also be omitted.
- I would leave the pointer in the header, this overhead is negligible of 1 entry per block.