
Chained Block Moves
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a residue byte (and therefore ignored) or it may be valid data that is
transferred to memory at the beginning of the next Block Move
instruction.
2.11.4 SCSI Output Data Latch (SODL) Register
For send data, the low-order byte of the SODL register holds the low-
order byte of a partial memory transfer which has not yet been
transferred across the SCSI bus. This stored data is usually married with
the rst byte of the next data send transfer, and both bytes are sent
across the SCSI bus at the start of the next data send block move
command.
2.11.5 Chained Block Move SCRIPTS Instruction
A chained Block Move SCRIPTS instruction transfers consecutive data
send or data receive blocks. Using the chained block move instruction
facilitates partial receive transfers and allows correct partial send
behavior without additional op code overhead. Behavior of the chained
Block Move instruction varies slightly for sending and receiving data.
For receive data (Data In for initiator or Data Out for target), a chained
Block Move instruction indicates that if a partial transfer occurred at the
end of the instruction, the WSR ag is set.The high order byte of the last
SCSI transfer is stored in the SCSI Wide Residue (SWIDE) register
rather than transferred to memory. The contents of the SWIDE register
should be the rst byte transferred to memory at the start of the chained
block move data stream. Since the byte count always represents data
transfers to/from memory (as opposed to the SCSI bus), the byte
transferred out of the SWIDE register is one of the bytes in the byte
count.
If the WSR bit is cleared when a receive data chained Block Move
instruction is executed, the data transfer occurs similar to that of the
regular block move instruction. Whether the WSR bit is set or clear, when
a normal block move instruction is executed, the contents of the SWIDE
register is ignored and the transfer takes place normally. For “N”
consecutive wide data receive Block Move instructions, the 2nd through
the Nth Block Move instructions should be chained block moves.