MIPS simulator does not support subtraction command

[JackMorganNZ]

Description

The text for the MIPS assembly and simulator interactives recommend trying to do subtraction of two numbers for advanced students. However when using the sub (also tried subu) command, the result when running the commands in the MIPS simulator is:

Unsupported R-type instruction

The simulator interactive should either handle the sub command, or the text should be altered.

To replicate this issue:

1. Go to MIPS simulator.
2. Enter the following text and click 'Simulate Execution':

00400000: <main>    ; <input:1> main:
00400000: 20080019  ; <input:5> li $t0, 25 # You can change the 10
00400004: 20090014  ; <input:6> li $t1, 20 # You can change the 20
00400008: 01092022  ; <input:10> sub $a0, $t0, $t1
0040000c: 20020001  ; <input:14> li $v0, 1
00400010: 0000000c  ; <input:18> syscall
00400014: 20020000  ; <input:21> li $v0, 0
00400018: 03e00008  ; <input:22> jr $ra

It may be worth contacting the original author of the interactive for help if needed.

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