DEC 4000 AXP Service Manual page 99

The causes for each of the machine check/interrupts are as follows. The system
control block (SCB) vector through which PALcode transfers control to the
operating system is shown in parentheses.
Processor Machine Check (SCB: 670)
Processor machine check errors are fatal system errors and immediately crash
the system.
• The DECchip 21064 microprocessor detected one or more of the following
uncorrectable data errors:
– Uncorrectable B-cache data error
– Uncorrectable memory data error (CU_ERR asserted)
– Uncorrectable data from other CPU's B-cache (CU_ERR asserted)
• A B-cache tag or tag control parity error occurred
• Hard error status was asserted in response to:
– A read data parity error
– System bus timeouts (NOACK error bit asserted)—The bus responder
detected a write data or command address error and did not acknowledge
the bus cycle.
System Machine Check (SCB: 660)
A system machine check is a system detected error, external to the DECchip
21064 microprocessor and possibly not related to the activities of the microproces-
sor. It occurs when C_ERROR is asserted on the system bus.
Fatal errors:
• The I/O module detected a system bus error while serving as system bus
commander:
– System bus timeouts (NOACK error bit asserted)—The bus responder
detected a write data or command address error and did not acknowledge
the bus cycle
– Uncorrectable data (CU-ERR asserted) from responder
• Any system bus device detected a command/address parity error
• A bus responder detected a write data parity error
• Memory or I/O system bus gate array detected an internal error (SYNC error)
Error Log Analysis 4–3