ESP8266 Community Forum

I'm using a NodeMCU and the arduino IDE and want to write data to flash...

I assume using SPIFFS with a file system etc means that it's not a quick to write data as writing to the flash directly?

I want to be able to write data to flash (up to 200KB as 1 "file") and read it back later - it's never going to leave the device so it doesn't need to be a specific file format.

If I use ESP.flashRead / ESP.flashWrite and ESP.flashSectorErase and handle byte alignment myself, can I assume it will be quicker than using SPIFFS? If so, how do I determine where in the flash is safe to write? How do I swap flash banks if that's necessary and do I need to select a module configuration that doesn't include a reserved area for SPIFFS?

I'd really appreciate any guidance...

Yes, using direct flash sectors would be faster than SPIFFS.
If you don't mind loosing your Raw data when doing an OTA, I would recommend using the Flash space just above the SPIFFS.

Hi Martin,

Thanks for confirming that it should be faster. If I can assume this is the correct place to get the official memory map:

http://www.espressif.com/en/support/exp ... ted-guide#

where is SPIFFS located and how can I tell where it ends? I assume to use it I'll need to swap flash banks or does ESP.flashWrite work on physical sectors of the SPI memory?

Thanks

SPIFFS and other memory mapping are described here : https://github.com/esp8266/Arduino/blob ... esystem.md
For specific SPIFFS address locations, you need to look in LD scripts depending of your Flash configs, for example, if you have a 4M module and use 1M SPIFFS, the script is https://github.com/esp8266/Arduino/blob ... sh.4m1m.ld.
This LD script shows _SPIFFS_start = 0x40500000 and _SPIFFS_end = 0x405FB000.
Knowing that OTA will use the space just above _SPIFFS_start with size of the sketch, you can assume that writing your raw data somewhere like 0x40300000, it is pretty safe that even OTA won't overwrite it.