• Menus and Toolbar: Most menu items have equivalent toolbar icons. If the function of a toolbar icon is not obvious, just hover the mouse over it and a tool tip will soon appear. Nearly all menu items also have keyboard shortcuts. Any menu item not appropriate in a given situation is disabled.
• Editor: MARS includes a basic text editor. It supports a single font which can be modified by selecting Editor from the Settings menu (new in Release 3.3). Notice on the bottom border that the cursor line and column position is maintained and there is a checkbox to show line numbers. They are displayed outside the editing area. If you use an external editor, MARS provides a convenience setting that will automatically assemble a file as soon as it is opened. Check the Settings menu.
• Message Areas: There are two tabbed read-only message areas at the bottom of the screen. The Run I/O tab is used at runtime for displaying console I/O as program execution progresses. User console input is typed into a pop-up dialog then echoed to the message area. The MARS Messages tab is used for other messages such as assembly or runtime errors and informational messages.
• MIPS Registers: MIPS registers are displayed at all times, even when you are editing and not running a program. While writing your program, this serves as a useful reference for register names and their conventional uses (hover mouse over the register name to see tool tips). There are three register tabs: the Register File (integer registers $0 through $31 plus LO, HI and the Program Counter), selected Coprocesor 0 registers (exceptions and interrupts), and Coprocessor 1 floating point registers.
• Assembly: Select Assemble from the Run menu or the corresponding toolbar icon to assemble the file currently in the Edit tab. Prior to Release 3.1, only one file could be assembled and run at a time. Releases 3.1 and later provide a primitive Project capability. To use it, go to the Settings menu and check Assemble operation applies to all files in current directory. Subsequently, the assembler will assemble the current file as the "main" program and also assemble all other assembly files (*.asm; *.s) in the same directory. The results are linked and if all these operations were successful the program can be executed. Labels that are declared global with the ".globl" directive may be referenced in any of the other files in the project. There is also a setting that permits automatic loading and assembly of a selected exception handler file.
• Execution: Once a MIPS program successfully assembles, the registers are initialized and three windows in the Execute tab are filled: Text Segment, Data Segment, and Program Labels. The major execution-time features are described below.
• Labels Window: Display of the Labels window (symbol table) is controlled through the Settings menu. When displayed, you can click on any label or its associated address to center and highlight the contents of that address in the Text Segment window or Data Segment window as appropriate (new in Release 3.3).

The assembler and simulator are invoked from the IDE when you select the Assemble, Go, or Step operations from the Run menu or their corresponding toolbar icons or keyboard shortcuts. MARS messages are displayed on the MARS Messages tab of the message area at the bottom of the screen. Runtime output is displayed on the Run I/O tab. Runtime input is entered through a pop-up dialog box then echoed to the Run I/O tab.

This document is available for printing on the MARS home page http://www.cs.missouristate.edu/MARS/.