This is an assembly puzzler I made during a 6 hour game jam hosted by UMD Game Dev club. The theme is crabs.

There are 5 registers:

1. A

Deneral purpose accumulator. Default argument for some op codes as documented below.

2. M

Motor control. Your crab can only crawl sideways. M controls its movement. If it's positive, then it moves to the right and vice versa.

Note: movement is only actuated for every cycle after M register has been set positive.

Example:

MOV 1 M     ; no movement
NOP         ; moves 1 to the right
NOP         ; moves 1 to the right
MOV 0 M     ; moves 1 to the right
NOP         ; stands still
MOV -10 M   ; stands still
NOP         ; moves 1 to the left

3. V, H

General purpose accumulator. I was gonna build other mechanics such as object detection but it got too complicated.

4. R

Stores rotation modulo 4. 0 is down, 1 is left, 2 is up, 3 is right.

1. LABEL:

Denotes position in code. Labels cannot be followed by other instructions(unlike zachtronics games).

Example:

MOV 10 A
L:
SUB 1 A
JGZ L

2. MOV

Example:

MOV 1 A
MOV R A

3. ADD, SUB

   ADD 1 A ADD A A SUB 1 M

4. NEG reg

Negates value in register

NEG M

5. NOP

No operation. Also known as noop

6. JMP label

Point the instruction pointer to specified label.

7. JEZ

Jump if A is 0

8. JNZ

Jump if A is not 0

9. JGZ

Jump if A > 0

10. JLZ

Jump if A <> 0

11. JRO

Unconditional relative jump with immediate value or value from register.

JRO -1      ; jump to previous instruction
JRO 1       ; jump to following instruction
JRO A       ; relative to jump the instruction stored in A

12. RCW

Rotate clockwise

12. RCC

Rotate counterclockwise

The first level can be solved using this code:

MOV -1 M
L:
JMP L

Use CTRL+RETURN to step through your code.

Press ESC or CTRL+C to stop debugger.