Vax 613 0S Instruction Manual Page 177

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Actions taken by hardware for a DMA abort:
~err -> option
uncorr interrupt -> CPU
error logged in FADR, TCEREG, and IR
DMA is aborted
Actions taken by hardware for an I/O error:
uncorr interrupt -> CPU
error logged in FADR, TCEREG, and IR
write is aborted, bad read data is returned
Actions taken by hardware for an invalid I/O address error:
uncorr interrupt -> CPU
error logged in FADR, TCEREG, and IR
reads and writes will have UNPREDICTABLE results
Actions taken by hardware for a corrected ECC error:
corr interrupt -> CPU
error logged in FADR, TCEREG, and IR
DMA is continued
The programming requirements on DMA error are:
All errors assert Uncorr Interrupt to the CPU. Errors also stop DMA until
the state machines are idle.
PALcode is activated, builds frame with r=1 or 0, clearing ISR, unlocking
other registers.
Machine check handler wakes up, must put information from ISR, other
DMA-related registers in a slot-specific area of memory that the option-level
driver can interrogate.
Machine check handler exits or halts system.
Driver can now wake up, since its IPL was lower than machine check handler
Driver interrogates option registers, then slot-specific memory area.
Driver clears slot-specific memory area, synchronizing access, so that the
driver cannot interrogate the slot-specific area of memory before it is written
by the machine-check handler in the case of errors.
SCSI DMA read operations from memory using scatter/gather maps must
include a valid guard page after the end of the actual buffer space if
prefetching of DMA read data is enabled.
All option-level I/O drivers must follow the rules outlined in the previous
table note.
Hardware Exceptions and Interrupts 10–11
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