Note 2: System Bus Write-Data Cycle Failures - DEC 4000 AXP Service Manual

Analysis:
All bus nodes check command/address parity during the command/address
cycle.
• _CA_NOACK errors without respective command/address parity errors are
most likely caused by problems in the bus commander, such as programming
errors, address generation, and the like. You should consider the context of
the error; for example, a software fault may cause the system to crash each
time you run a particular piece of software.
• _CA_NOACK errors with all responders reporting command/address parity
errors are most likely caused by a bus commander failure or bus failure.
• _CA_PAR errors, without respective command/address NOACKs are most
likely the result of a failing buffer within the device reporting the isolated
CA_PAR error.

4.4.2 Note 2: System Bus Write-Data Cycle Failures

Synopsis:
System Bus Write Data failures can be reported by the bus commander,
responders, or both.
• By commander: _WD_NOACK—Write-Data No-Ack
Commander did not receive an acknowledgment to write-data cycle. A bus
buffer failure on the bus commander is the probable cause.
• By responders: _WD_PAR—Write-Data Parity Error
Responder detected a parity error during the write-data cycle. The bus was
corrupted by commander module (I/O or CPU), backplane, or responder
module (I/O, memory, or CPU).
Analysis:
Only the addressed bus responder checks write-data parity.
• _WD_NOACK (write-data NOACK) errors without respective WD_PAR (write-
data parity) errors are most likely caused by problems in the bus commander.
However, there is a small probability that the responder could be at fault.
Note
Note
Error Log Analysis 4–13