Avago Technologies LSI53C876E User Manual
Page 44
2-22
Functional Description
Synchronous SCSI Send –
Step 1.
If the DMA FIFO size is set to 88 bytes, look at the
and
registers and calculate
if there are bytes left in the DMA FIFO. To make this calculation,
subtract the seven least significant bits of the
register from the 7-bit value of the
register. AND the result with 0x7F for a byte count
between 0 and 88.
If the DMA FIFO size is set to 536 bytes (bit 5 of the
register it set), subtract the 10 least significant
bits of the
register from the 10-bit
value of the DMA FIFO Byte Offset Counter, which consists of
bits [1:0] in the
register and bits [7:0]
of the
register. AND the result with 0x3FF
for a byte count between 0 and 536.
Step 2.
Read bit 5 in the
and
registers to determine if any bytes are left in the
register. If bit 5 is set in the
SSTAT0 or SSTAT2 register, then the least significant byte or
the most significant byte in the
register is full, respectively. Checking this bit also reveals bytes
left in the
register from a
Chained Move operation with an odd byte count.
Step 3.
Read bit 6 in the
and
registers to determine if any bytes are left in the
SODR register. If bit 6 is set in the
or
register, then the least significant
byte or the most significant byte in the SODR register is full,
respectively.
Asynchronous SCSI Receive –
Step 1.
If the DMA FIFO size is set to 88 bytes, look at the
and
registers and calculate
if there are bytes left in the DMA FIFO. To make this calculation,
subtract the seven least significant bits of the
register from the 7-bit value of the
register. AND the result with 0x7F for a byte count
between 0 and 88.