UNIVERSITY OF CALIFORNIA, DAVIS
Department of Electrical and Computer Engineering
EEC 170 Introduction to Computer Architecture Fall 2019
Getting Started with RARS
(RISC-V Assembler, Runtime and Simulator)
Setting up the Environment
1. Download the java executable for a recent release of RARS from
https://github.com/TheThirdOne/rars/releases/download/v1.3.1/rars1_3_1.jar
2. RARS is distributed as an executable jar so, you will need at least Java 1.8 to run it. Install both of these packages Java Development kit and Java Runtime Environment. Update the environment variables in your computer by adding the path to binaries in these packages.
3. Our department workstations have these packages are already installed, go to /software/classtools/EEC170 directory and type the following command in the terminal to launch the IDE.
java -jar rars1_3_1.jar
Usage
1. Run “rars_1_3_1.jar” to open the IDE as shown picture below.
2. The IDE provides basic editing, assembling and execution capabilities. Refer to
help section for detailed explanation of the features. Help > RARS > IDE
3. Optional: RARS can also be used through command line, for this, you need to
download the source code from https://github.com/TheThirdOne/rars/releases. Then, run “build-jar.sh” file in the folder to build the repository. After a successful build, “rars.jar” will be created.
Refer to https://github.com/TheThirdOne/rars/blob/master/help/Command.html for usage directives.
Running and Debugging
Let us work with a simple assembly code, which increments a register for a certain number of times and saves it in the stack.
1. Click on File > New to create a new file. Type the following code into editor and save it.
# Declare the listed label(s) as global to enable referencing from other files
.globl main
main: # The Program execution starts from here
li t0, 100
li t1, 170
# Initial Value of t1 is pushed into the stack
sw t1,4(sp)
# Loop which increments t1 for a certain number of times
loop:
addi t1,t1,1
addi t0,t0,-1
bne t0,zero,loop
# Final Value of t1 is pushed into the stack
sw t1,8(sp)
2. To assemble the code, click on, Run > Assemble. Once the program successfully assembles, the registers are initialized and three windows in the Execute tab are filled with: Text Segment, Data Segment, and Program Labels.
3. You can run complete program by clicking on Run > Go or step by step Run > Step.
● In Step mode, the next instruction to be simulated is highlighted and memory content displays are updated at each step.Select the Go option if you want to simulate continually. It can also be used to continue simulation from a paused (step, breakpoint, pause) state.
● Breakpoints are easily set and reset using the checkboxes next to each instruction displayed in the Text Segment window.
● When running in the Go mode, you can select the simulation speed using the Run Speed slider.
● You can also pause or stop simulation at any time using the Pause or Stop features.
● You have the ability to interactively step “backward” through program execution one instruction at a time to “undo” execution steps.
● When program execution is paused or terminated, select Reset to reset all memory cells and registers to their initial.
For more information refer to click on Help > IDE > Debugging.
4. Your values in registers and memory locations should match the following after
execution.
Address 0x7ffff000 corresponds to a location in stack, it contains the initial value of t1 i.e 170 or 0x0aa and the address 0x7ffff004( 0x7ffff000 + Value(+4) ) contains final value of t1 i.e 270 or 0x10e.
5. You can use an editor of your choice to write a code, to import the code click on,
File > Open.
6. To close a file on the RARS editor, select a file and click on File > Close.