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esp32/README: Update README to describe auto filesystem sizing.

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Signed-off-by: Damien George <damien@micropython.org>
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Damien George
2025-06-12 10:52:32 +10:00
parent 6201e77999
commit fa393feaed
1 changed files with 24 additions and 0 deletions
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ports/esp32/README.md
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@@ -221,6 +221,30 @@ import machine
antenna = machine.Pin(16, machine.Pin.OUT, value=0)
```
Partition table and filesystem size
-----------------------------------
ESP32 firmware contains a bootloader, partition table and main application
firmware, which are all stored in (external) SPI flash. The user filesystem
is also stored in the same SPI flash. By default, MicroPython does not have
a fixed entry in the ESP32 partition table for the filesystem. Instead it
will automatically determine the size of the SPI flash upon boot, and then --
so long as there is no existing partition called "vfs" or "ffat" -- it will
create a partition for the filesystem called "vfs" which takes all of the
remaining flash between the end of the last defined partition up until the
end of flash.
This means that firmware built for, say, a 4MiB flash will work on any
device that has at least 4MiB flash. The user "vfs" filesystem will then
take up as much space as possible.
This auto-detection behaviour can be overridden: if the ESP32 partition
table does contain an entry called "vfs" or "ffat" then these are used for
the user filesystem and no automatic "vfs" partition is added. This is
useful in cases where only the MicroPython ESP32 application is flashed to
the device (and not the bootloader or partition table), eg when deploying
.uf2 files.
Defining a custom ESP32 board
-----------------------------