Improve USB MSC initiator support #496
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Early exit all functions when no drives have been found. This avoids watchdog timeouts when USB host keeps polling.
SCSI spec allows CD/MSG/IO signals to change state between byte transfers. Previously this would cause initiator mode to abort transfer. On Seagate ST-296N it was observed that 6 µs long glitches on IO signal occur when the drive is trying to perform bad sector recovery. This commit uses a combination of methods to tolerate glitches on these signals, while still aborting the transfer if it hangs.
There is no need to fail a read when the drive reports RECOVERED_ERROR.
Was running out of RAM. Moved initiator mode main loop to flash, it doesn't really affect performance.
Convert sense key to textual description. For example: -- SCSI Initiator read on target 0 failed with status -1 and sense_key 0x03 (MEDIUM_ERROR) for drive reported medium errors.
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Made the USB MSC initiator mode more robust.
Tested against ST-296N drive that has a large amount of bad blocks with ddrescue.
Reading is slow because of a lot of medium errors reported by the drive, but is able to correctly handle the error statuses and transfer progresses.