Laptop User Manual

Preserving the Debugger Operating Environment

MVME166IG/D2 4-11

Exception Vectors Used by 166Bug

The exception vectors used by the debugger are listed below. These vectors

must reside at the specified offsets in the target program’s vector table for the

associated debugger facilities (breakpoints, trace mode, etc) to operate.

NOTE: These depend on what the Vector Base Register (VBR) is set to

in the VMEchip2.

When the debugger handles one of the exceptions listed in Table 4-2, the target

stack pointer is left pointing past the bottom of the exception stack frame

created; that is, it reflects the system stack pointer values just before the

exception occurred. In this way, the operation of the debugger facility

(through an exception) is transparent to users.

Table 4-2. Exception Vectors Used by 166Bug

Vector

Offset

Exception 166Bug Facility

$10 Illegal instruction Breakpoints (used by GO, GN, GT)

$24 Trace Trace operations (such as

T, TC, TT)

$80-$B8 TRAP #0 - #14 Used internally

$BC TRAP #15 System calls

$NOTE Level 7 interrupt ABORT pushbutton

$NOTE Level 7 interrupt AC Fail

$DC FP Unimplemented Data Type Software emulation and data type

conversion of floating point data.