Seagate Ultra 320 - Manual (Page 139)

Parallel SCSI Interface Product Manual, Rev. A 125
6.2.3 SPI data information unit
The SPI data information unit (see Table 52) contains data.
The detection of a BUS FREE phase following a SPI data information unit by a SCSI initiator port shall be
equivalent to the initiator receiving a DISCONNECT message.
The detection of a QAS REQUEST message following a SPI data information unit by a SCSI initiator port shall
be equivalent to the initiator receiving a DISCONNECT message.
Table 52: SPI data information unit
[1] The Data field may contain any type of information (e.g., parameter lists, mode pages, user data).
[2] The iuCRC field shall use the algorithm defined in Subsection 11.3 of ANSI SCSI Parallel Interface (SPI-
5), T10/1525D. If the iuCRC Interval field of the SPI L_Q information unit contains a value greater than
zero and less than the data length, then there is an iuCRC field at each iuCRC interval in addition to the
iuCRC shown in this table. These additional iuCRC fields are not shown in this table.
6.2.4 SPI data stream information unit
The SPI data stream information unit (see Table 53) contains data.
All the SPI data stream information units transferred after a SPI L_Q information unit with a type of data stream
shall be the size indicated in the Data Length
field of the SPI L_Q information unit.
If the data transfer size is not a multiple of the data length, the SCSI target shall end the stream at a data length
boundary and shall send a new SPI L_Q with a smaller data length to finish the data transfer. The new SPI L_Q
may or may not be sent during the current physical connection.
During write streaming, the sequence of SPI data stream information units shall end with any change to the C/
D, I/O, or MSG signals on a SPI data stream information unit boundary. If during write streaming SPI data
stream information nits a SCSI initiator detects a REQ transition after transmitting the last iuCRC for a SPI data
stream information unit that initiator shall transmit the next SPI data stream information unit.
During read streaming, the SCSI target shall end a sequence of SPI data stream information units by perform-
ing one of the following:
a. should assert the P_CRCA signal before the end of the current SPI data stream information unit bound-
ary; or
b. may change the C/D, I/O, or MSG signals on a SPI data stream information unit boundary.
If, during the last SPI data stream information unit of a read stream, the P_CRCA signal was not asserted and
a SCSI initiator detects a REQ transition after receiving the last iuCRC for a SPI data stream information unit,
that initiator shall receive the next SPI data stream information unit. If, during the last SPI data stream informa-
Bit
Byte
7 6 5 4 3 2 1 0
0 MSB
DATA [1]
n LSB
n+1 MSB
iuCRC [2]
n+2
n+3
n+4 LSB