Background Monitors; Foreground Monitors - HP 7700 Series User Manual

Background Monitors

A background monitor is an emulation monitor which overlays the
processor's memory space with a separate memory region. Entry into
the monitor is normally accomplished by jamming the monitor
addresses onto the processor's address bus.
Usually, a background monitor will be easier to work with in starting a
new design. The monitor is immediately available upon powerup, and
you don't have to worry about linking in the monitor code or allocating
space for the monitor to use the emulator. No assumptions are made
about the target system environment; therefore, you can test and debug
hardware before any target system code has been written. All of the
processor's address space is available for target system use, since the
monitor memory is overlaid on processor memory, rather than
subtracted from processor memory. Processor resources such as
interrupts are not taken by the background monitor.
However, all background monitors sacrifice some level of support for
the target system. For example, when the emulation processor enters
the monitor code to display registers, it will not respond to target
system interrupt requests. This may pose serious problems for
complex applications that rely on the microprocessor for real-time,
non-intrusive support. Also, the background monitor code resides in
emulator firmware and can't be modified to handle special conditions.

Foreground Monitors

A foreground monitor may be required for more complex debugging
and integration applications. A foreground monitor is a block of code
that runs in the same memory space as your program. Foreground
monitors allow the emulator to service real-time events, such as
interrupts or watchdog timers, while executing in the monitor. For
most multitasking, interrupt intensive applications, you will need to use
a foreground monitor.
You can tailor the foreground monitor to meet your needs, such as
servicing target system interrupts. However, the foreground monitor
does use part of the processor's address space, which may cause
problems in some target systems. You must also properly configure
the emulator to use a foreground monitor (see the "Configuring the
Emulator" chapter and the examples in this appendix).
A-2 Using A Foreground Monitor