Added a timer tool

[zacharyselk]

A tool added to the RARS GUI that simulates a timing core, accessed via MMIO, that can handle timing interrupts as referenced in #3. It should (hopefully) be entirely compliant to the RISC-V spec aside from handling privilege levels (ie it does not check for user, supervisor, and machine level permissions).

(Also this is my first time attempting to code in Java so the code might look a bit odd / might be implemented in an odd way)

[TheThirdOne]

From a quick review, it looks pretty good. The main issue I see is that build/ and rars.jar were committed. I should have put them in the gitignore when I made the build script. I'll removed the references when I merge this in.

Additionally, it would be nice to have an example program that uses the tool. If you don't already have a program you were testing with, I can make one without much trouble; your help page should be sufficient documentation.

[zacharyselk]

Great to hear! I added a small example program, timerTest.s, that uses the tool.

[TheThirdOne]

This was merged in with 5e5f218.

Thanks for the PR. The interrupt side of RARS definitely needed some attention and this is a good step towards improving it.

[colbac8]

I'm trying to use the timer tool starting from the test file timertool.s, but I've some questions about it. What I'm trying to do is generate a timer interrupt every 5 seconds and each time that the interrupt happens, the handler prints a message (e.g., hello...similar with the timertool.s program).

When I start the timertool.s program, it seems to remain in the loop forever and prints only the time and the newline. No timing interrupts are generated after 5 seconds (i.e., the label "hello" is never printed.). Do I have to enable something in RARS or do something else to make the timertool.s program work?

[zacharyselk]

Yes, in RARS to use timer interrupts you need to enable and run the Timer Tool. This is done by going to Tools > Timer Tool and then clicking the Connect to Program button then clicking the Play button.

[colbac8]

Yes, I tried by using the timer tool but it didn't work in the version rars_1_3_1. I downloaded the latest version (1.4) and it now works! Thank you