ESP32 Forum

I'm flashing a bin to a nvs partition called 'mfg'.

I discovered (after much head bashing) that I cannot flash a bin to a partition that is the size of the partition. Otherwise you get a ESP_ERR_NVS_NO_FREE_PAGES error when you try to init the partition.

My partition table looks like this:
Right now I'm writing a 0x1000 byte bin to the mfg partition.

But what I'd like to do is size a mfg partition with 0x1000 bytes and write a smaller bin to that partition as I only need to write a couple small strings.

So my question is: what is the minimum amount of blank space I need to leave at the end of a partition?

Or, with a partition sized at 0x1000 bytes, what is the maximum size of the bin I can flash to that partition?


P.S. is that the correct way to have both readonly and encrypted flags set on a partition?

You can specify multiple flags by separating them with a colon. For example, encrypted:readonly.

https://docs.espressif.com/projects/esp ... html#flags

It's occurred to me that ESP_ERR_NVS_NO_FREE_PAGES might mean that you need at least one page free.

Digging further it looks like a standard page size is 256 bytes:
https://docs.espressif.com/projects/esp ... l#mkspiffs

So in theory the maximum size of a bin in a minimum sized read-only NVS partition would be 0x900 bytes - given the minimum size of a read-only NVS partition is 0x1000 (https://docs.espressif.com/projects/esp ... ml#subtype)

But, if you use esp-idf's supplied partition generation tool... bin sizes must be a multiple of 0x1000 bytes (https://docs.espressif.com/projects/esp ... on-default)

So practically, the minimum NVS size for a read only partition is actually 0x2000 bytes because you need at least 0x100 bytes free and you have to flash binaries in multiples of 0x1000...

Tha page size of the flash memory is actually 4k, i.e. 0x1000.
According to the docs, you don't need a free page if the partition is flagged read-only.

Tha page size of the flash memory is actually 4k, i.e. 0x1000.
According to the docs, you don't need a free page if the partition is flagged read-only.

Could you link where it says that? It says you don’t need a free page, but it doesn’t init without error if it doesn’t have it. I don’t feel comfortable ignoring the error because I don’t know exactly what else might trigger the error that I shouldn’t ignore.