MIPS BNE 机器码转换

Question

I am attempting to convert about 25 lines of a MIPS program from machine code into instructions.

When I convert the machine code of 0x1620fff9 , it yields the following: 000101 10001 00000 1111 1111 1111 1001

I understand this is I-format, and the instruction is BNE with a target register of $17 and a source of $0 , however the immediate/address is what I am confused about.

As 1111 1111 1111 1001 is a signed number, its two's complement yields a result of -7 . I just dont know what to do with that result. The MARS simulator needs a label for where it should branch to, but I am unclear as to what to do. The program I am converting only has a main function and a print function.

Thanks

Answer 1

So it turns out that MARS and QTSpim handle those instructions differently:

• MARS always jumps from the instruction after the branch instruction which is exactly what a pipelined machine is supposed to do;

• QtSPIM jumps from the branch instruction, which is easier to understand.

• Under MARS, bne instruction is 0x1620fff8, while under QtSPIM, it is 0x1620fff9.

Our professor made concessions for the differing results, but I thought that this may be useful to someone in the future.