Tomalesbay uses the MIPS o32 calling convention. I'm not sure what convention, if any, our textbook teaches, but I would recommend to not trust it. I've attached two files below. The first is a *.pdf that was distributed to last year's class. The second is a *.pdf that I wrote that goes over a few examples to further emphasize the first *.pdf. The latter shouldn't contradict the former, but, if it does, let me know.
Note that violating the calling convention won't necessarily mean that your program won't work. For grading purposes, you will be marked down for violating the convention, even if your program works.