Livt.Usb

src/mass-storage/ReadOnlyScsiCommand.lvt

namespace Livt.Usb.MassStorage

/**
 * USB's transparent SCSI read-only subset. CDB bytes are emitted in wire order;
 * multibyte SCSI fields are big endian. No arbitrary or write opcode is exposed.
 */
component ReadOnlyScsiCommand
{
	public const TEST_UNIT_READY: byte = 0x00
	public const REQUEST_SENSE: byte = 0x03
	public const INQUIRY: byte = 0x12
	public const READ_CAPACITY: byte = 0x25
	public const READ_BLOCK: byte = 0x28

	/** Exact input length for the supported fixed-size, read-only command profile. */
	public static fn DataLength[](opcode: byte) int
	{
		if (opcode == TEST_UNIT_READY) {
			return 0
		}

		if (opcode == REQUEST_SENSE) {
			return 18
		}

		if (opcode == INQUIRY) {
			return 36
		}

		if (opcode == READ_CAPACITY) {
			return 8
		}

		if (opcode == READ_BLOCK) {
			return 512
		}

		return -1
	}

	/** Returns six/ten-byte CDB length, or zero for unsupported commands. */
	public static fn Length[](opcode: byte) byte
	{
		if (opcode == TEST_UNIT_READY || opcode == REQUEST_SENSE || opcode == INQUIRY) {
			return 6
		}

		if (opcode == READ_CAPACITY || opcode == READ_BLOCK) {
			return 10
		}

		return 0
	}

	/** Returns one CDB byte, including zero padding through byte fifteen. */
	public static fn GetByte[](opcode: byte, lba: uint, index: byte) byte
	{
		if (Length(opcode) == 0 || index >= 16) {
			return 0
		}

		if (index == 0) {
			return opcode
		}

		if (index == 4 && opcode == INQUIRY) {
			return 36
		}

		if (index == 4 && opcode == REQUEST_SENSE) {
			return 18
		}

		if (opcode == READ_BLOCK) {
			if (index == 2) {
				return (lba >> 24) as byte
			}

			if (index == 3) {
				return (lba >> 16) as byte
			}

			if (index == 4) {
				return (lba >> 8) as byte
			}

			if (index == 5) {
				return lba as byte
			}

			if (index == 8) {
				return 1
			}
		}

		return 0
	}
}