Using Software Breakpoints - HP 64746 User Manual

Chapter 6: Using the Emulator

Using Software Breakpoints

Using Software Breakpoints
Software breakpoints provide a way to accurately stop the execution of your
program at selected locations.
Note Version A.04.00 or greater of the HP 64700 system firmware provides support for
permanent as well as temporary breakpoints. If your version of HP 64700 system
firmware is less than A.04.00, only temporary breakpoints are supported.
Software breakpoints are implemented in the 68302 emulator by replacing opcodes
with TRAP instructions. You can configure the emulator to use one of 16 different
TRAP instructions for software breakpoints. The default emulator configuration
specifies that the TRAP #0FH is used for software breakpoints.
In order to successfully set a software breakpoint, the emulator must be able to
write to the memory location specified. Therefore, software breakpoints cannot be
set in target memory while the emulator is reset, and they can never be set in target
ROM. (You can, however, copy target ROM to emulation memory by storing the
contents of target ROM to an absolute file, re-mapping the range as emulation
RAM, and loading the absolute file.)
When you set a software breakpoint, the emulator replaces the opcode at the
address specified with the TRAP instruction. When the emulator detects a read
from the appropriate vector table location (TRAP instruction has executed in the
user program), execution breaks to the monitor.
If the TRAP was generated by a software breakpoint, a message containing the
address of the breakpoint is displayed on the status line, and, if the breakpoint is
temporary, the original opcode is restored in the user program. If the breakpoint is
permanent, it remains active. A subsequent run or step command will execute
from the breakpoint address.
If the TRAP was not inserted as the result of a modify software_breakpoints set
command (in other words, it is part of the user program), the "Undefined software
breakpoint" message is displayed on the status line. To continue with program
execution, you must run or step from the user program's TRAP instruction vector
address.
Another way to break user program execution at a certain point is to break on the
analyzer trigger.
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