zephyr: Mount all disks and flash partition, formatting if necessary.

Existing C code in `main.c` only mounts a flash filesystem if one exists,
and doesn't do anything if the 'storage' partition is not formatted.

This commit moves the mounting logic from `main.c` to frozen code using
`modules/_boot.py` and adds the formatting of a previously unformatted
partition if the mount fails.

Every available disk (in the newly added `DiskAccess.disks` tuple) will be
mounted on separate mount points (if they're formatted), and the 'storage'
flash partition (if any) will be mounted on /flash (and will be formatted
as LFS2 if necessary).

Also, `sys.path` will be updated with appropriate 'lib' subdirectories for
each mounted filesystem.

The current working directory will be changed to the last `DiskAccess.disk`
mounted, or to /flash if no disks were mounted.

Then `boot.py` and `main.py` will be executed from the current working
directory if they exist.

Thanks to @VynDragon for the logic in `zephyr/zephyr_storage.c`.

Signed-off-by: Ned Konz <ned@metamagix.tech>

1 files changed, 48 insertions, 8 deletions

diff --git a/docs/zephyr/tutorial/storage.rst b/docs/zephyr/tutorial/storage.rst
index 7fd449226..835d239b6 100644
--- a/docs/zephyr/tutorial/storage.rst
+++ b/docs/zephyr/tutorial/storage.rst
@@ -8,6 +8,27 @@ Zephyr DiskAccess or FlashArea (flash map) APIs depending on which the board sup
 
 See `vfs Filesystem Mounting <https://docs.micropython.org/en/latest/library/vfs.html?highlight=vfs#filesystem-mounting>`_.
 
+Automatic Filesystem Mounting
+------------------------------
+
+MicroPython on Zephyr automatically attempts to mount available storage at startup:
+
+1. **Flash storage** (if available): Automatically mounted at ``/flash`` using the
+   littlefs2 filesystem. If the filesystem doesn't exist, it will be created
+   automatically.
+
+2. **Disk storage** (such as SD cards): Automatically detected and mounted at
+   ``/<disk_name>`` (e.g., ``/sd`` for SD cards).
+
+3. **Working directory**: The working directory is set to the mounted disk if
+   available, otherwise to ``/flash`` if flash storage is available.
+
+4. **Module search path**: The ``sys.path`` is automatically updated to include
+   ``/<disk>/lib`` for each mounted disk and ``/flash/lib`` for flash storage.
+
+This automatic mounting is performed by the ``_boot.py`` module at startup. For most
+use cases, you don't need to manually mount filesystems.
+
 Disk Access
 -----------
 
@@ -19,17 +40,26 @@ For use with SD card controllers, SD cards must be present at boot & not removed
 be auto detected and initialized by filesystem at boot. Use the disk driver interface and a
 file system to access SD cards via disk access (see below).
 
+The available disk names can be accessed via the ``DiskAccess.disks`` attribute, which contains
+a tuple of available disk names (e.g., ``('SDHC',)`` or ``('SD',)``).
+
 Example usage of FatFS with an SD card on the mimxrt1050_evk board::
 
     import vfs
     from zephyr import DiskAccess
-    bdev = zephyr.DiskAccess('SDHC')        # create block device object using DiskAccess
+
+    # List available disks
+    print(DiskAccess.disks)                 # prints available disk names, e.g., ('SDHC',)
+
+    bdev = DiskAccess('SDHC')               # create block device object using DiskAccess
     vfs.VfsFat.mkfs(bdev)                   # create FAT filesystem object using the disk storage block
     vfs.mount(bdev, '/sd')                  # mount the filesystem at the SD card subdirectory
     with open('/sd/hello.txt','w') as f:    # open a new file in the directory
         f.write('Hello world')              # write to the file
     print(open('/sd/hello.txt').read())     # print contents of the file
 
+Note: In most cases, disks are automatically mounted at startup and manual mounting is not necessary.
+
 
 Flash Area
 ----------
@@ -41,16 +71,26 @@ API is recommended (see below).
 This class uses `Zephyr Flash map API <https://docs.zephyrproject.org/latest/reference/storage/flash_map/flash_map.html#>`_ and
 implements the `vfs.AbstractBlockDev` protocol.
 
+The available flash area names can be accessed via the ``FlashArea.areas`` dictionary, which maps partition
+labels to their IDs (e.g., ``{'storage': 1, 'scratch': 4}``).
+
 Example usage with the internal flash on the reel_board or the rv32m1_vega_ri5cy board::
 
     import vfs
     from zephyr import FlashArea
-    bdev = FlashArea(FlashArea.STORAGE, 4096)   # create block device object using FlashArea
-    vfs.VfsLfs2.mkfs(bdev)                      # create Little filesystem object using the flash area block
-    vfs.mount(bdev, '/flash')                   # mount the filesystem at the flash storage subdirectory
-    with open('/flash/hello.txt','w') as f:     # open a new file in the directory
-        f.write('Hello world')                  # write to the file
-    print(open('/flash/hello.txt').read())      # print contents of the file
+
+    # List available flash areas
+    print(FlashArea.areas)                          # prints available areas, e.g., {'storage': 1, 'scratch': 4}
+
+    bdev = FlashArea(FlashArea.areas['storage'], 4096)   # create block device object using FlashArea
+    vfs.VfsLfs2.mkfs(bdev)                               # create Little filesystem object using the flash area block
+    vfs.mount(bdev, '/flash')                            # mount the filesystem at the flash storage subdirectory
+    with open('/flash/hello.txt','w') as f:              # open a new file in the directory
+        f.write('Hello world')                           # write to the file
+    print(open('/flash/hello.txt').read())               # print contents of the file
+
+Note: In most cases, the flash storage partition is automatically mounted at ``/flash`` at startup with
+automatic filesystem creation if needed, so manual mounting is not necessary.
 
 For boards such as the frdm_k64f in which the MicroPython application spills into the default flash storage
-partition, use the scratch partition by replacing ``FlashArea.STORAGE`` with the integer value 4.
+partition, use the scratch partition by replacing ``'storage'`` with ``'scratch'``.