Adapt the usbd-storage rp2040 example into pm-grid as a composite MIDI+MSC
device:
- Host sees a 1MB removable drive backed by the upper 1MB of flash (a
.filesystem region, NOLOAD so it stays out of the UF2 and survives reflashes).
- scsi_command handles the SCSI set (Inquiry / ReadCapacity10/16 /
ReadFormatCapacities / Read / Write / ModeSense / RequestSense / TestUnitReady).
Reads come from flash via raw pointer; writes accumulate a 4KB block then
erase+program the sector with rp2040-flash (wrapped in interrupt::free).
- Host owns the FAT format (formats on first use). Unblocks on-device persistence.
- Composite poll: usb_dev.poll([&mut midi, &mut scsi]); scsi.poll services commands.
Build fixes required by adding rp2040-flash:
- rp2040-hal 0.10 -> 0.11 (0.10 + rp2040-flash 0.6 both export the __aeabi_*/
__addsf3 ROM intrinsics -> duplicate symbols). No HAL API breakage.
- lto = false + codegen-units = 1 (fat-LTO tripped the same duplicate intrinsic).
UF2 stays ~257KB thanks to NOLOAD. defmt logs on block writes + unknown commands.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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