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Chapter 3 Transport Layer Implementation Details
Parallel SCSI
DLT-S4 Interface Reference Guide
13
Supported Task
Management for
Information Units
3
For more in information about supported task management for
information units (see
chapter 2, Task Management
).
Synchronous Data Transfer
Request
3
This extended message allows the tape drive and initiator to agree on the
values of the parameters relevant to synchronous transfers. The
SYNCHRONOUS DATA TRANSFER REQUEST
message has the format
shown in
figure 1
.
Figure 1 Synchronous Data
Transfer Request Message —
Data Format
A SCSI device initiates a
SYNCHRONOUS DATA TRANSFER REQUEST
message exchange whenever a previously arranged transfer agreement
may have become invalid. The agreement becomes invalid after any
condition that may leave the data transfer agreement in an indeterminate
state, such as:
Note:
The ANSI SPI-4 standard prohibits target devices from
initiating negotiations using the
PARALLEL PROTOCOL
REQUEST
message. Instead, targets are required to negotiate
using the
WIDE DATA TRANSFER REQUEST
and
SYNCHRONOUS DATA TRANSFER REQUEST
messages. The
DLT-S4 tape drive initiates negotiations starting with a
WIDE
DATA TRANSFER REQUEST
message before transferring any
data if transfer parameters have not been established or have
been lost (see
SPI-4
.
Bit
Byte
7
6
5
4
3
2
1
0
0
Extended Message Identifier (01h)
1
Length (03h)
2
SYNCHRONOUS DATA TRANSFER REQUEST (01h)
3
Transfer Period
4
Transfer REQ/ACK Offset