
2-40
Functional Description
2.2.12.2 Synchronous SCSI Send
The DMA FIFO is the only location where data can reside when a phase
mismatch occurs during a synchronous SCSI send transfer. To determine
the number of bytes remaining in the DMA FIFO, read the
DMA FIFO
Byte Count (DFBC)
register. This 16-bit, read only register contains the
actual number of bytes remaining in the DMA FIFO. To recover from all
other error conditions the DMA FIFO should be cleared by setting bit 2
(CLF) in
Chip Test Three (CTEST3)
and the I/O should be retried.
If the Wide SCSI Send (WSS) bit in the
SCSI Control Two (SCNTL2)
register is set when a phase mismatch occurs, then adjustments must be
made to the previous block move, not the current block move loaded into
DCMD/DBC. To recover the byte of chain data in the outbound chain byte
holding register, the previous block move byte count should be set to one
and the address set to the last data address for that block move.
2.2.12.3 Asynchronous SCSI Receive
When a phase mismatch occurs during an asynchronous SCSI receive,
the only data that may remain in the device is a potential wide residue
byte in the
SCSI Wide Residue (SWIDE)
register. If bit 0 (WSR) in
SCSI
Control Two (SCNTL2)
is set, then the SWIDE register contains a
residual byte. This byte can be flushed by executing a block move
instruction with a byte count of one. To recover from all other error
conditions the DMA FIFO should be cleared by setting bit 2 (CLF) in
Chip
Test Three (CTEST3)
and the I/O should be retried.
2.2.12.4 Synchronous SCSI Receive
When a phase mismatch occurs during a synchronous SCSI receive
transfer no data recovery operation is necessary. All data, including chain
bytes from chained block moves, are flushed from the device prior to the
phase mismatch occurring. To recover from all other error conditions, the
DMA FIFO should be cleared by setting bit 2 (CLF) in
Chip Test Three
(CTEST3)
, the SCSI FIFO should be cleared by setting bit 1 (CSF) in
SCSI Test Three (STEST3)
, and the I/O should be retried.
2.2.13 SCSI Bus Interface
The SYM53C1010 performs SE and LVD transfers.