System Resource Conflicts - IBM 2179 Hardware Maintenance Manual

v Multiple messages occur when the first error causes additional errors. Follow
the suggested action of the first error displayed.

System resource conflicts

System failures occur when there are system resource conflicts with the following:
v Interrupt Request Queue (IRQ)
v Direct Memory Access (DMA)
v I/O Address
v ROM and RAM Addresses.
IRQ
v Assigns a unique interrupt request line to every I/O device (line numbers range
from 0 to 15).
v Interrupts the processor to force it to service the request.
v Handles interrupts on a priority basis (low numbers have the highest priority).
v Queues interrupt request.
IRQ conflicts occur when there are multiple assignments to the same interrupt
level. If there is an IRQ conflict, the system will hang. Use the systems diagnostics
to check for multiple assignments to the same interrupt level before replacing any
hardware component.
DMA
v Accesses the memory by bypassing the processor. This allows the processor
more time for applications and programs.
v Accesses memory directly from the serial and parallel ports on some systems.
v Accesses memory directly from some adapters using a DMA channel. This
allows the adapter to operate faster.
v Provides from 4 to 15 DMA channels. The number varies depending on the
system.
If multiple assignments of the same DMA channel occur, the system will hang.
Use the system diagnostics to check for multiple assignments to the same DMA
channel before replacing any hardware components.
I/O address
A unique I/O address is assigned to each system component.
If multiple assignments of the same I/O address occur, the system will hang. Use
the DOS MEM command to check for multiple assignments to the same I/O
address before replacing any hardware component.
ROM and RAM Addresses
Adapter cards with processors can contain RAM and ROM. If the adapter cards
have onboard memory, then the following are true.
v ROM contains operating instructions for the adapter I/O.
v RAM is used for buffering.
Two adapters using the same memory area will cause a failure. This failure might
appear as a hardware failure.
Chapter 8. Related service information
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