Do sd_flash_write or sd_flash_page_erase verify the result of the flash operation?

[Marius Heil]

Hi,

do sd_flash_page_erase or sd_flash_write provide any guarantees that the command has executed successfully or should I do a manual check to verify if the page was really erased or the data was written correctly?

Thanks, Marius

[Sigurd]

Hi,

There is no automatic verification of flash content (sd_flash_page_erase /sd_flash_write will not read back the data), so this is something you can add if you want (though I have not heard of this being a problem, and we don't do that ourselves).

[Sigurd]

Embedded NOR flash typically implements a kind of programming "state-machine". Verify operation typically consist in controlling the memory cells under program, and checks if they have reached the target threshold voltage. If the target voltage inside the memory cell is not reached, it will typically retry the write operation. See this book chapter from Springer. Nordic is not the company designing the flash used inside our chips, so HW flash algorithms are Intellectual property (IP) owned by the flash vendor company.

What happens when you exceed the spec is that the probability of bit flipping happening gradually increases. In the latest FDS drivers, we have implemented CRC checks on read and write, so that you can verify that the data you once wrote, is matching the one you read back later. See this link.

But again, note that NOR flash is very reliable, and does not generally need any error correction in software/firmware