Set and Reset the Bypass CCU Check Stop Mode: Output X'79', byte 1, bit 4
set to 1 prevents CCU hard stop and MOSS interrupt from being set due to a CCU
hard check. To reset the bypass mode, the control program must execute an
output X'79' instruction with byte 1, bit 5 set to 1.
However, MOSS can also issue a bypass CCU check stop or a CCU hard stop.
The following table shows the resulting CCU mode.
Notes:
1. Adapter interface check stop causes adapter interface errors to be handled as
hard errors.
2. See “CCU Error Handling” and “Program Errors” on page 2-47 for more infor-
mation.
Set and Reset the Level 1 Adapter Mask: Program level 1 interrupt requests
caused by a check condition in an adapter (scanner or CA) can be masked by
using an output X'7E', byte 1, bit 1. To unmask the level 1 requests, the control
program must execute an output X'7F' (reset mask bits) with byte 1, bit 1 set to 1.
MOSS
Program
CCU Mode Result
-
-
Bypass
Bypass
Bus stop (1)
Bus stop (1)
Bus stop
and bypass
-
Bypass
-
Bypass
-
Bypass
Normal (2)
Bypass
Bypass
Bypass
Normal (2)
Normal (2)
Bypass
CCU Error Handling
The following are the basic principles of the CCU error handling strategy:
CCU-Detected Hardware Errors: They are high-severity errors, usually hardware
failures. They stop the CCU. No retry is performed. The error indication latches
are sensed by MOSS through the LSSD path.
CCU-Detected Not Hard Errors: They are low-severity errors, either program
errors, or IOC bus errors, or MOSS 'interconnection' errors. They do not stop the
CCU. They can be encountered during the following operations:
1. MOSS operations through the MIOC or adapter operations (AIOs) performed
with the MOSS flag.
These errors are reported to MOSS only.
2. Program instructions and adapter operations (non-MOSS):
These errors are reported to the program only.
Checking the Checkers
All checkers can be checked by the LSSD scan path.
2-44
IBM 3745 Models 130, 150, 160, 170, and 17A: Hardware Maintenance Reference
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