IBM Multiprise 3000, Справочное руководство, Страница: 47 / 264

Byte 0, Bits 0 and 1: Specify what types of write operations to permit in the
channel program. The 3390 has a restriction:
Note: "If these bits are ‘11’, byte 1, bits 3 through 5 are ignored and bypass cache
is forced."
This restriction assures that Write HA and Write R0 commands that can alter the
physical volume layout (by changing alternate track pointers for example), are
hardened beyond the cache before channel end and device end are presented.
Internal Disk manages the physical volume layout internally, without the data
contained in Write HA and Write R0, and does not need the restriction. If bits are
"11", Byte 1, bits 3 through 5 are honored and may specify a cache management
algorithm other than bypass cache.
Byte 0, Bit 2: Must be zero, or the command is terminated with unit check status.
The sense data contains command reject with format 0, message 4.
Table 4-5. Mask Byte Definition
Byte 0 Bits Bit
Value Mask Byte Function
0–1 Write Control
00 Permit all write operations except
Write HA and Write R0
01 Inhibit all write operations
10 Permit update write operations only
11 Permit all write operations
2 0 Reserved
3–4 Seek Control
00 Permit all Seek commands
01 Permit Seek Cylinder and Seek Head
commands only
10 Permit Seek Head commands only
11 Inhibit all seek commands and
multitrack operations
5–6 Access Authorization
00 Normal Authorization
01 Device Support Authorization
10 Diagnostic Authorization
11 Device Support Authorization –
Inhibit Retry
7 Program–Controlled Interruption (PCI) fetch
mode
0 Not PCI fetch mode
1 PCI fetch mode
Chapter 4. Command Descriptions
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