HP 64783A, User Manual

Page: 669 / 816

Dealing with keep-alive circuitry while using the
background monitor
Another thing to watch for when using the background monitor is the triggering of
a target system keep-alive circuit because monitor bus cycles are hidden.
Depending on how a keep-alive circuit operates, the monitor may cause a problem.
The symptoms for different keep alive circuits may not show up in the same way.
Keep-alive circuits that monitor accesses on the bus or require a certain address to
be accessed probably will fail when you use the background monitor. Keep-alive
circuits that make sure bus cycles complete will not fail. If the keep-alive circuit
generates a bus error or an interrupt, the monitor will not be affected immediately.
If the keep-alive circuit asserts reset instead, monitor operation will be affected
immediately, although there may be no apparant symptoms if reset is only asserted
temporarily because the monitor will be reentered as soon as reset is deasserted.
If you suspect a problem with a keep-alive circuit, there is a configuration option
that can make the background monitor periodically cause a read access to a
particular address. If you do need a particular address to be read for the keep-alive
function, make sure the address you give will respond with memory strobes when
accessed.
cf monkaa=0deadad0
Retry the reset into monitor with this configuration enabled. If there is any sort of
problem with the keep-alive access, it will probably show up as a wait state at the
keep-alive address. If this happens, check the timing on that particular cycle. The
keep-alive address may respond with a bus error without adversly affecting monitor
operation.
Chapter 18: Connecting the Emulator to a Target System
Installing Emulator Features
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