Precautions - IBM AT 5170 Technical Reference

procedure may not be suitable when adapters that are being
serviced by the corrupt handler are actively generating interrupts,
since unserviced interrupts lock up that interrupt level.
ROS Considerations
Adapters with their handlers residing in ROS may choose to
implement chaining by storing the 4 byte FPTR (plus the FIRST
flag if it is sharing interrupt 7 or 15) in on-adapter latches or
ports. Adapter ROS without this feature must first test to see
that it is the first in the chain. If it is the first in the chain, the
adapter can complete the link; if not, the adapter must exit its
routine without linking.
Precautions
The following precautions must be taken when designing
hardware or programs using shared interrupts:
•
Hardware designers should ensure the adapters:
Do not power up with the ENA line active or an
interrupt pending.
Do not generate interrupts that are not serviced by a
handler. Generating interrupts when a handler is not
active to service the adapter causes the interrupt level to
lock up. The design relies on the handler to clear its
adapter's interrupt and issue the Global Rearm.
Can be disabled so that they do not remain active after
their application has terminated.
• Programmers should:
Ensure that their programs have a short routine that can
be executed with the AUTOEXEC.BAT to disable their
adapter's interrupts. This precaution ensures that the
adapters are deactivated if the user reboots the system.
System
Board 1-17