CODEWITHSUNDEEP
hexmips
hiero
hiero

Reputation: 23

How to simply convert MIPS instruction to 32bits hex number

I'm working with ASM/MIPS technology and I want to train myself to conversion.

I wanna convert MIPS instructions to a 32bits hexadecimal number. For example, I want to change sub$t0,$zero,$t1 to a hexa number.

I've find a lot of solutions, but everything is different. Any idea ?

Upvotes: 1

Views: 2496

Answers (1)

Niklas Rosencrantz
Niklas Rosencrantz

Reputation: 26644

The MIPS sub instruction subtracts two registers and stores the result in a register.sub $d,$s,$t means $d = $s - $t

sub = function code 34 (see manual), 22 in hex, 100010 in bin (6 bits)
$t0 = 8 in decimal, 8 in hex, 01000 in bin (5 bits)
$zero = 0 in decimal, 0 in hex, 00000 in bin (5 bits)
$t1 = 9 in decimal, 9 in hex, 01001 in bin (5 bits)

So the machine code for your instruction is 01001 01000 00000 100010

For R-format instructions, the opcode, or "operation code" is always zero. rs, rt, and rd correspond to the two source and one destination registers.

The source sub$t0,$zero,$t1 therefore translates to 0x00094022 in hexadecimal notation.

Explanation

Every MIPS instruction is 32bits and translates to a 32bits number that can be written as machine code in hexadecimal format.

The instruction sub (subtract) has opcode 0x22. Therefore the rightmost digits has to be 22 (see above that they are).

sub is an instruction type R. This means the R instructions are used when all the data values used by the instruction are located in registers.

All R-type instructions have the following format:

OP rd, rs, rt

Where "OP" is the mnemonic for the particular instruction (in this case sub). rs, and rt are the source registers, and rd is the destination register. In this case, the sub instruction is used as:

sub $t0, $zero, $t1

In other words, your instruction means "subtract t1 from 0 and put the result in t0".

If you want to swap the values of two registers you can do it as follows:

.text
.globl  __start
__start:

sw      $t0, x
sw      $t1, y
lw      $t0, y
lw      $t1, x
.data
x:
.word   0x000000FF
y:
.word   0xABCDE080

If you want to put the content in $t0 also in $t1, you can use the or instruction:

lui  $t0, 0x0123
or   $t1, $zero, $t0

Upvotes: 1

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