Fix to allow remount when usb enabled but not msc

[bmeisels]

Addresses #2509.
storage remount now checks if USB MSC is mounted.
Would appreciate more testing before merging.

[dhalbert]

This looks good to me! @bmeisels one question: Did you test this by powering the board by battery and having USB plugged in, and then disconnecting and attempting the remount()? Assuming you did that, I'm happy to approve.

[tannewt]

Thank you for the PR! Unfortunately I think some of the TinyUSB terminology confused things a bit.

Instead of modifying usb.c, please modify usb_msc_flash.c instead. It is already tracking when the host "ejects" the drive. You'll need to set ejected to true on init and then exposed a similar function to check it from storage.

[tannewt]

I don't think this needed. mount doesn't mean filesystem mount here unfortunately. It is plugged/unplugged.

[bmeisels]

@tannewt @dhalbert i have edited the patch according to your suggestion.
The test i performed was the following:

1. connect initialized (with no code.py) device (with a battery) to Windows PC
2. connected to repl
3. called storage.remount("/", False) at this point still fails because the drive is mounted
4. ejected the drive without unplugging from pc
5. called storage.remount("/", False) which now works
6. called storage.remount("/", True)
7. unplugged and reinserted device
8. wrote code.py to drive
9. performed soft reset through terminal which resulted in the code.py running as expected.

I hope this is now correct

[tannewt]

I'd prefer usb_msc_enabled to be usb_msc_ejected to match the internal name. I can update it tomorrow if that is easiest.

[bmeisels]

Implemented the requested changes. I did not retest on actual hardware.

[tannewt]

Thank you!