Motorola MVME166IG/D2 - Manual (Page 68)

Debugger General Information
3-22 MVME166 Single Board Computer Installation Guide
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The Multiprocessor Address Register (MPAR), located in shared RAM
location of $804 offset from the base address the debugger loads it at, contains
the second of two longwords used to control communication between
processors. The MPAR contents specify the address at which execution for the
remote processor is to begin if the MPCR contains a G or B. The MPAR is
organized as follows:
At power-up, the debug monitor self-test routines initialize RAM, including
the memory locations used for multi-processor support ($800 through $807).
The MPCR contains $00 at power-up, indicating that initialization is not yet
complete. As the initialization proceeds, the execution path comes to the
"prompt" routine. Before sending the prompt, this routine places an R in the
MPCR to indicate that initialization is complete. Then the prompt is sent.
If no terminal is connected to the port, the MPCR is still polled to see whether
an external processor requires control to be passed to the dual-port RAM. If a
terminal does respond, the MPCR is polled for the same purpose while the
serial port is being polled for user input.
An ASCII G placed in the MPCR by a remote processor indicates that the Go
Direct type of transfer is requested. An ASCII B in the MPCR indicates that
breakpoints are to be armed before control is transferred (as with the GO
command).
In either sequence, an E is placed in the MPCR to indicate that execution is
underway just before control is passed to RAM. (Any remote processor could
examine the MPCR contents.)
If the code being executed in dual-port RAM is to reenter the debug monitor,
a TRAP #15 call using function $0063 (SYSCALL .RETURN) returns control to
the monitor with a new display prompt. Note that every time the debug
monitor returns to the prompt, an R is moved into the MPCR to indicate that
control can be transferred once again to a specified RAM location.
$804 * * * * (MPAR)