Quantum 1200 Series DAT Autochanger Podręcznik Użytkownika Pobierz pdf (Strona 40)

Supported SCSI Messages SDLT 600 SCSI Interface Guide

3-12 January 2005 81-81200-02 REV A01

3.2.15 SYNCHRONOUS DATA TRANSFER REQUEST (extended

message 01h)

This extended message allows the SDLT 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 3-5.

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 SDLT 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.

Figure 3-5. 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:

• After any SCSI reset condition

• After a TARGET RESET message

• After a power cycle

• After a WIDE DATA TRANSFER REQUEST message exchange.

The SYNCHRONOUS DATA TRANSFER REQUEST message exchange establishes an agreement

between two SCSI devices on the clocking of the data used for DATA phase transfer between them.

Bit

Byte

7 6 5 4 3 2 1 0

Extended Message Identifier (01h)

(see

Figure 3-1)

1 Length (03h)

2 SYNCHRONOUS DATA TRANSFER REQUEST (01h)

3 Transfer Period

4 Transfer REQ/ACK Offset

1 2 ... 35 36 37 38 39 40 41 42 43 44 45 ... 293 294

Brak uwag

Quantum 1200 Series DAT Autochanger Podręcznik Użytkownika Strona 40