3. Running the simulator

The following is a guided tour to running the simulator. sim6811 on unix is used as example.

3.1 Starting up

From the top directory, enter the commands

        % cd test/arch/m6811
        % ../../../src/boards/sim6811 68mon.s19
        PC=e06b A:B=0000 X=0000 Y=0000 SP=0000 CCR=d0(SXhInzvc) [0]
        e06b    8e 00 f6       lds  #00f6       STACK
      

The simulator is ready to run. The CPU state is printed with registers (PC .. CCR), clock cycles (0) on the first line. All numbers are printed in hexadecimal (except for clock cycles). On the next line follows memory address, the unassembled instruction in hexadecimal and mnemonic format, and a symbol string the right.

3.2 Getting on-line help

        >h
        Breakpoint commands
                b                       - list breakpoints
                b [+|-] [addr]          - toggle, set(+) or clear(-) breakpoint
                B s|c [addr]            - set/clear breakpoint
                B C                     - clear all breakpoints
                B E|e                   - break on error/no break on error
        Memory commands
                md [addr [count]]       - memory display
                mm  addr [hh hh..]      - memory modify
                u  [addr [count]]       - unassemble
        Run commands
                g [addr]                - go
                s                       - step over subroutines
                t                       - trace one instruction
                R                       - jump to reset vector
        Stack commands
                c                       - print call stack
                C                       - print function calls on/off toggle
                w [min max]             - set stack watches
        Miscellanous commands
                l                       - list symbols
                !Command                - pass 'Command' to shell
                q                       - quit
        Register commands:
                r p|a|b|c|d|x|y|s val   - modify register
        External event commands
                i sci [hh|"ss"] ..        - io input hex digits or strings to SCI
                i sci print               - print contents of SCI buffer
                i spi [hh|"ss"] ..        - io input hex digits or strings to SPI
                i spi print               - print contents of SPI buffer
                i out [hex|ascii|\ascii]  - io output mode for displaying data
      

3.3 Displaying the source

The simulator can only display assembly language and convert numbers to global symbols.

        >u
        e06b    8e 00 f6       lds  #00f6       STACK
        e06e    86 20          ldaa #20 SP
        e070    ba 10 28       oraa  1028       SPCR
        e073    b7 10 28       staa  1028       SPCR
        e076    86 30          ldaa #30
        e078    b7 10 2b       staa  102b
        e07b    86 0c          ldaa #0c PTOF
        e07d    b7 10 2d       staa  102d       SCCR2
        e080    7f 00 fd       clr   00fd       FLAG
        e083    86 7e          ldaa #7e
      

3.4 Stepping through an instruction

        >t
        PC=e06e A:B=0000 X=0000 Y=0000 SP=00f6 CCR=d0(SXhInzvc) [3]
        e06e    86 20          ldaa #20 SP
      

Pressing Enter wil repeat the last command and is well suited for stepping through several instructions in sequence.

3.5 Setting break point

We want to debug the routine GETIN, so we set a breakpoint at its entry point, and then list all breakpoints.

        >b GETIN
        Breakpoint at e1d8 set

        >b
        Active breakpoints:
        e1d8    GETIN
      

3.6 Running until breakpoint

        >g
        e06e: Running...

                       68Mon V1.2 (C) 1992 Keith Vasilakes

          SXHINZVC  AB AA  IX   IY   PC   SP
          11100110  A4 7E E6A4 7EE6 A47E 0000
        >Breakpoint before code execution, address e1d8!
        Subroutine: e1d8 GETIN
        PC=e1d8 A:B=3e03 X=e1fc Y=0000 SP=00f2 CCR=c8(SXhiNzvc) [8936]
        e1d8    b6 10 2e       ldaa  102e       SCSR
      

The text printed between Running... and Breakpoint, is output from the program running under the simulator.

3.7 Displaying the call stack

        >c
        Call stack:
        e1cd    CHRIN
        e1d8    GETIN
      

We are in routine GETIN, that was called from routine CHRIN.

3.8 Entering IO port data

There are two ways of entering IO port data into the simulator:

• Stop the simulator and change the IO port values, or in the case of serial interrupt, enter data into the serial buffer of the simulator.
• Serial data can be entered on standard input while the simulator is running.