user manual

Debugger General Information

B-24

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 each 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.

GCSR Method

A remote processor can initiate program execution in the local

MVME177 dual-port RAM by issuing a remote GO command

using the VMEchip2 Global Control and Status Registers (GCSR).

The remote GO command causes the following sequence:

❏ Remote processor places the MVME177 execution address in

general purpose registers 0 and 1 (GPCSR0 and GPCSR1)

❏ Remote processor sets bit 8 (SIG0) of the VMEchip2 LM/SIG

❏ MVME177 installs breakpoints and begins execution

The result is identical to the MPCR method (with status code B)

described in the previous section.

The GCSR registers are accessed in the VMEbus short I/O space.

Each general purpose register is two bytes wide, occurring at an

even address. The general purpose register number 0 is at an offset

of $8 (local bus) or $4 (VMEbus) from the start of the GCSR

registers. The local bus base address for the GCSR is $FFF40100. The

VMEbus base address for the GCSR depends on the group select

value and the board select value programmed in the Local Control