HP 743 Series Technical Reference Manual For Oems page 148

High Priority Machine Check (HPMC) was of type bus error with the "check Type" field equal
to "20000000", the "sysReqAdd" field equal to "00109180", and the "cache", "tlb", "bus",
"assists", "asstState", "sysRsAdd" fields set to zero.
In rare circumstances, Models 742i and 747i allow non-specified data lines to float, resulting
in HP-UX panic. Most often, this behavior occurs when Models 743i and 744 are generating
IACK as a D08 or D16 interrupter. To avoid this behavior, do not have Models 743i and 744
as interrupt handlers for Models 742i and 747i or configure (in the kernel interface driver that
is generating the interrupt) Models 742i and 747i as D32 interrupters.
Models 742i and 747i have an internal (SGC) bus watchdog timer set to 1 ms by the boot
ROM (PDC) code. When the PA processor starts a read or write transaction to VME I/O
space, the watchdog timer starts. If the total time from acquiring the VME bus (arbitration
time) to cycle completion time (DTACK or BERR) exceeds 1 ms, the system crashes with a
HPMC. In HP-UX, the resulting panic dump message indicates a SGC bus error HPMC (this
behavior cannot be changed). In either HP-UX or HP-RT, the operating system cannot
recover from an HPMC error.
The system must be configured so that Models 742 or 747 always get the VME bus and com-
plete the first transaction in less than 1 ms. This is done through vme_config in HP-UX, and
by setting specific defines, such as bus request priority, to set bus behavior in HP-RT.
Models 743i and 744 have an internal bus protocol called "split" that overcomes the 1 ms
problem in Models 742i and 747i, but the processor appears hung until the VME cycle com-
pletes.
Current releases of HP-UX and HP-RT do not support the use of the location monitor capa-
bility. However, Models 742i and 747i and Models 743i and 744 handle monitoring VME
locations differently:
Models 742i and 747i ASIC, if enabled, generate a local interrupt when the VME
space that is defined for the location monitor is accessed. It also DTACKS the VME
cycle.
Models 743i and 744 ASIC, if enabled, generate a local interrupt when the space
that is defined for the location monitor is accessed. It does not+ DTACK the VME
cycle.
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Product Design Considerations
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