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114 lines
5.8 KiB
HTML
114 lines
5.8 KiB
HTML
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<title>MARS 4.5 help contents
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<h3>MARS - Mips Assembly and Runtime Simulator</h3>
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<h4>Release 4.5</h4>
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<h4>August 2014</h4>
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<h4>Interactive Debugging Features</h4>
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<p>
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MARS provides many features for interactive debugging through its Execute pane.
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Features include:
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<ul>
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<li>In <i>Step</i> mode, the next instruction to be simulated is highlighted and
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memory content displays are updated at each step.</li>
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<li>Select the <i>Go</i> option if you want to simulate continually.
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It can also be used to continue simulation
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from a paused (step, breakpoint, pause) state.</li>
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<li>Breakpoints are easily set and reset using the check boxes next to each instruction displayed
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in the Text Segment window. <i>New in Release 3.8:</i> You can temporarily suspend breakpoints
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using Toggle Breakpoints in the Run menu or by clicking the "Bkpt" column header in the Text Segment
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window. Repeat, to re-activate.</li>
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<li>When running in the <i>Go</i> mode, you can select the simulation
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speed using the Run Speed slider. Available speeds range
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from .05 instructions per second (20 seconds between steps) up to 30
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instructions per second, then above this offers an "unlimited" speed.
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When using "unlimited" speed, code highlighting and memory display updating
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are turned off while simulating (but it executes really fast!).
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When a breakpoint is reached, highlighting and updating occur.
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Run speed can be adjusted while the program is running.</li>
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<li>When running in the <i>Go</i> mode, you can pause or stop
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simulation at any time using the <i>Pause</i> or <i>Stop</i> features.
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The former will pause execution and update the display, as if you
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were stepping or at a breakpoint. The latter will terminate execution
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and display final memory and register values. If running at "unlimited"
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speed, the system may not respond immediately but it will respond.</li>
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<li>You have the ability to interactively step "backward" through program execution
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one instruction at a time to "undo" execution steps. It will buffer up to 2000 of the most
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recent execution steps (this limit is stored in a properties file and can be changed).
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It will undo changes made to MIPS memory, registers or condition flags,
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but not console or file I/O. This should be a great debugging aid.
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It is available anytime execution is paused and at termination (even if terminated due to
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exception).
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<li>When program execution is paused or terminated, select <i>Reset</i>
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to reset all memory cells and registers to their initial post-assembly values.
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In fact, Reset is implemented by re-assembling the program.</li>
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<li>Memory addresses and values, and register values, can be viewed in either decimal
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or hexadecimal format. All data are stored in little-endian byte order (each
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word consists of byte 3 followed by byte 2 then 1 then 0). Note that each word
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can hold 4 characters of a string and those 4 characters will appear in the
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reverse order from that of the string literal.</li>
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<li>Data segment contents are displayed 512 bytes
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at a time (with scrolling) starting with the data segment base address (0x10010000).
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Navigation buttons are provided to change the display to the next
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section of memory, the previous, or back to the initial (home) range. A combo box is
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also provided to view memory contents in the vicinity of the stack pointer
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(contents of MIPS $sp register), global pointer (contents of MIPS $gp register),
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the heap base address (0x10040000), .extern globals (0x10000000),
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the kernel data segment (0x90000000), or memory-mapped IO (MMIO, 0xFFFF0000).
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<em>Starting with Mars 4.4,</em> raw text segment contents can also be displayed.</li>
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<li>Contents of any data segment memory word and almost any MIPS register can be modified by
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editing its displayed table cell. Double-click on a cell to edit it and press the Enter key
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when finished typing the new value. If you
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enter an invalid 32-bit integer, the word INVALID appears in the cell
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and memory/register contents are not affected. Values can be entered
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in either decimal or hexadecimal (leading "0x"). Negative hexadecimal
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values can be entered in either two's complement or signed format. Note
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that three of the integer registers (zero, program counter, return address)
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cannot be edited.</li>
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<li><em>New in 4.4</em> If the setting for Self-Modifying Code is enabled
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(disabled by default, look in the Settings menu), text segment binary
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code can be modified using the same technique described above. It can also
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be modified by double-clicking on a cell in the Text Segment display's Code
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column.</li>
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<li>Contents of cells representing floating point registers can be edited
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as described above and will accept valid hexadecimal or decimal floating point
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values. Since each double-precision register overlays two single-precision
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registers, any changes to a double-precision register will affect one or both
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of the displayed contents of its corresponding single-precision registers.
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Changes to a single-precision register will affect the display of its
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corresponding double-precision register. Values entered in hexadecimal
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need to conform to IEEE-754 format. Values entered in decimal are entered
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using decimal points and E-notation (e.g. 12.5e3 is 12.5 times 10 cubed).</li>
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<li>Cell contents can be edited during program execution and once accepted
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will apply starting with the next instruction to be executed.</li>
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<li>Clicking on a Labels window entry will cause the location associated with
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that label to be centered and highlighted in the Text Segment or Data Segment
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window as appropriate. Note the Labels window is not displayed by default but
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can be by selecting it from the Settings menu.</li>
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</ul>
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<hr>
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<p>
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This document is available for printing on the MARS home page
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<tt><b>http://www.cs.missouristate.edu/MARS/</b></tt>.
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</body>
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</html> |