Upload Filesystem Image uploads at wrong address (+0x1000)

tuttut · April 18, 2025, 10:33pm

I am trying to get USB MSC with FFat running on an ESP32-S3. As I use a small Flash variant (4MB Flash), I am using a custom partitions table as following:

# Name,   Type, SubType, Offset,  Size, Flags
nvs,      data, nvs,     0x9000,  0x5000,
otadata,  data, ota,     0xe000,  0x2000,
app0,     app,  ota_0,   0x10000, 0x140000,
app1,     app,  ota_1,   0x150000,0x140000,
ffat,     data, fat,     0x290000,0x160000,
coredump, data, coredump,0x3F0000,0x10000,

The ffat section starts at 0x290000. When I use the “Upload Filesystem Image” option or invoking “platformio run --target uploadfs --environment esp32-s3 -v”, the following command is run:

"/Users/xxx/.platformio/penv/bin/python" "/Users/xxx/.platformio/packages/tool-esptoolpy@src-e9520c52db7d0ecbb98379d0d58b38a9/esptool.py" --chip esp32s3 --port "/dev/cu.usbmodem11201" --baud 921600 --before default_reset --after hard_reset write_flash -z --flash_mode dio --flash_freq 80m --flash_size detect 2691072 .pio/build/esp32-s3/fatfs.bin

There occurs the wrong address because 2691072 = 0x291000 and the filesystem is placed at 0x291000 - this is exact one flash memory block too late - it should go to 0x290000. Interestingly, FFat.begin() can work with that, however, if there is no filesystem and I do FFat.begin(true) it formats the filesystem itself and then it starts at 0x290000 in memory.
This is not a big issue until you want to expose the FAT via USB MSC. Then the host computer will read the first block from 0x290000 which is just filled with 0xff and can not open the volume. I can try to work-around and dynamically set a different offset for MSC, depending on where the FFat VBR is located - but this is not nice - is this a known bug or a feature?

maxgerhardt · April 18, 2025, 10:46pm

github.com/platformio/platform-espressif32

builder/main.py

ec69109ed


      
          # FFat specific offsets, see:
          # https://github.com/lorol/arduino-esp32fatfs-plugin#notes-for-fatfs
          if filesystem == "fatfs":
              env["FS_START"] += 4096
              env["FS_SIZE"] -= 4096

tuttut · April 19, 2025, 12:02am

Thank you for pointing this out, then this behavior is due wear-leveling. I have added a search for the first flash block that starts with 0xeb to find the FAT start and added this offset to the LBA addresses of the onWrite and onRead functions of USB MSC. With that, both FAT format variants (via FFat.begin(true) and Filesystem uploader) are working also with USB Mass Storage. Thank you.