Running the program

Starting the program sim68k

To start the simulator just put the sim68k file in a directory which is in your path and type sim68k. You can open a binary 68000 file by typing sim68k <filename.s29>

The files executed (source-ed) at startup are:

• The configuration file which main purpose is to defines the hardware: memory, interfaces. The system file is located in <install_path>/sim68k.cfg or in the environment variable SIM68K_CONFIG.

• A file located in <install_path>/sim68k.start or in the environment variable SIM68K_START which contains all what you want to execute once the simulator is configured and before you get the control back. You can perform here any initialization of your choice, like customization of the GUI (keyboard bindings)

• If it exists and is readable, the file ~/.sim68k is sourced

• If it exists and is readable, the file ~/.sim68k.windows is sourced, otherwise, the simulator sets the windows to a default geometry

Graphical interface

The function of the components of the graphical interface should be mostly self-explanatory. There are menus, a toolbar, a source window, the registers, two memory dump, a command window to input commands and an info window to output message about the state or action of the simulator. Please see figure 1.

Figure 1: sim68k Graphical User Interface components

Source window

The source window contains the code disassembled. The line corresponding to the current Program Counter PC has a blue-sky background. You can set breakpoints in your assembler source. The line corresponding to a breakpoint has its text written in dark blue.

Click on the mouse button in the source window has the following action :

Left button:

sets the PC on the specified line

Middle button:

Toggle breakpoint on the specified line

Right button:

Pop-up menu which proposes the actions above

Registers

The register window displays the registers. The first eight bytes of the address pointed by the address registers are displayed on their right. You can change the format of display (left-click on the name of the register): a pop-up menu will appear to propose Hex (hexadecimal base), Dec (decimal base) or Bin which will dump the binary form of the register to the info window.

The flags of the Status Register are extracted, and you can set or clear them individually by clicking on it and choosing the command in the pop-up menu.

You can change the value of the register by clicking on them, typing in a numerical value and then return. If the entered value is correct, it will be displayed as the new value of the register. The syntax is case-insensitive and accepts most of the common numerical syntax (see table 1).

Table 1: Syntaxes for numerical input to change the registers

decimal	123789
octal	012345, @12345
hexadecimal	0xC1afE, $C1afE, 0C1afEh
binary	%0110110, 0110110b

Toolbar

The toolbar represented in figure 2 includes several buttons.

Figure 2: Toolbar of the simulator

Open File:

load a binary .s29 file into the memory of the simulator

Reload:

load a binary .s29 file into the memory of the simulator

Next:

execute one instruction, skipping subroutine (JSR and BSR)

Step:

execute one instruction, stepping into the subroutines

Run:

run the code but do not update the GUI of the 68000. The button is automatically replaced by a Stop button which you can press to interrupt the program. The program runs significantly faster in this mode. A breakpoints stops the execution of the program.

Trace:

run the code and update the GUI at each instruction. You can tune the speed of the execution and skip the subroutines if you check the corresponding button. You can press the Stop button to interrupt the program. A breakpoints stops the execution of the program.

Menus

The function of the menus should be quite self-explanatory. Let us just present the Tools and Options submenus.

The tools submenus displays the table of the Exception Vector in a new window, see figure 3

Figure 3: Exception vector table

The Options menu offers the following entries :

notify IPL:

display a message in the info window when an IPL occurs

notify other exception:

display a message in the info window when other exceptions than IPL occurs

Stop if IPL:

in Run or Trace mode, stop the execution if an IPL occurs

Stop if other exception:

in Run or Trace mode, stop the execution if an other exceptions than IPL occurs

Display Labels:

toggle the display of the labels or the hexadecimal code of the instruction on the column on the right of the address in the source window

Source Follows PC:

if this is set while in Trace mode, the simulator will arrange for the PC to be always visible in the source windows

Save current as default:

save current options settings into the file ~/.sim68k which will be automatically sourced at startup next time to resume the same options