Writing to a flash when receiving data via BLE

RE: Writing to a flash when receiving data via BLE

Proton — Thu, 19 Nov 2020 00:45:43 GMT

You probably don't know how the nrf_nvmc_write_bytes () and nrf_nvmc_write_words () functions work. It would be strange if they performed the same function and both wrote down words. But nrf_nvmc_write_bytes () writes individual bytes. You can verify this by writing "1" in both functions and looking at the memory:
nrf_nvmc_write_bytes (addr, massss, 1);
nrf_nvmc_write_words (addr + 40, massss, 1);
So I can choose whether to write to me in bytes or in words. And it's a pity that softdevice is not that advanced.

RE: Writing to a flash when receiving data via BLE

Hung Bui — Wed, 18 Nov 2020 13:03:24 GMT

Hi Proton,
No you don't have an option to choose between bytes or words but 32bit word is the smallest unit you can write with the NVMC on the nRF52 anyway. Here is the spec:
The NVMC is only able to write 0 to bits in the flash that are erased (set to 1). It cannot rewrite a bit back
to 1. Only full 32-bit words can be written to flash using the NVMC interface. To write less than 32 bits,
write the data as a full 32-bit word and set all the bits that should remain unchanged in the word to 1.
Note that the restriction on the number of writes (nWRITE) still applies in this case

If you don't use fstorage, you don't have to configure NRF_FSTORAGE_SD_MAX_WRITE_SIZE and can use sd_flash_write () directly, but as it's mentioned in the other case, we have a bug that if you write 1024 words in one call you may have an issue. Try to split it to two writes for example.

RE: Writing to a flash when receiving data via BLE

Proton — Wed, 18 Nov 2020 12:28:09 GMT

With the nrf_nvmc_write_bytes () and nrf_nvmc_write_words () functions, I have the right to choose whether to write in words or bytes. softdevice provides no choice?

I do not use the FSTORAGE functions and the file system, I want to choose where to write bytes myself.

NRF_FSTORAGE_SD_MAX_WRITE_SIZE will affect the sd_flash_write () write function too ??

RE: Writing to a flash when receiving data via BLE

Hung Bui — Tue, 17 Nov 2020 16:12:13 GMT

Hi Proton,

The size argument in sd_flash_write() is actually the number of words, not the number of bytes. So if you use 1024 it means it's 4096 bytes.

And we actually have an issue with a write with such size, have a look here: https://devzone.nordicsemi.com/f/nordic-q-a/48830/softdevice-assertion-failed

I would suggest to keep the number of bytes writing in one chunk to shorter. In our DFU example we use NRF_FSTORAGE_SD_MAX_WRITE_SIZE = 20

Note that fstorage automatically split the data into multiple chunks if the data is bigger than NRF_FSTORAGE_SD_MAX_WRITE_SIZE .