instructions

Instructions in the [as as yet unnamed] ISA

An example instruction looks like:

Hex - 8 3 7 2

Bin - 1000 0011 0111 0010

Shift r7 left 2 bits and store result in r3

Opcodes

Opcode	Instruction
0	Add
1	Subtract
2	And
3	Or
4	SetIfLess
5	SetIfEqual
6	ShiftLeft
7	ShiftRightLogical
8	ShiftRightArithmetic
9	SetLower
A	SetUpper
B	LoadWord
C	SaveWord
D	SetPcIf
E	SetPcIfNot
F	Special

Register instructions

Instruction in form:

Opcode	Destination register (d)	Source register 1 (s1)	Source register 2 (s2)

Opcode	Instruction	Operation	Notes
0	Add	d = s1 + s2
1	Subtract	d = s1 - s2
2	And	d = s1 & s2
3	Or	d = s1 | s2
4	SetIfLess	d = 1 if s1 < s2, 0 otherwise
5	SetIfEqual	d = 1 if s1 = s2, 0 otherwise
6	ShiftLeft	d = s1 << s2	Fills new right side bits with 0s
7	ShiftRightLogical	d = s1 >> s2	Fills new left side bits with 0s
8	ShiftRightArithmetic	d = s1 >> s2	Fills new left side bits with most significant bit

Set instructions

Instruction in form:

Opcode	Destination register (d)	8 bits value (v)

Opcode	Instruction	Operation	Notes
9	SetLower	Lower 8 bits of d set to v
A	SetUpper	Upper 8 bits of d set to v

Memory instructions

Instruction in form:

Opcode	Offset (o)	Target (t)	Address (a)

Opcode	Instruction	Operation	Notes
B	LoadWord	Loads M(r(a) + o) into r(t)	Addresses in words
C	SaveWord	Saves r(t) into M(r(a) + o)	Addresses in words

Special instructions

Instruction in form:

Opcode	Value1	Value2	Value3

Opcode	Instruction	Operation	Notes
D	SetPcIf	rPC set to value1 if r(value2) == r(value3)
E	Unused
F	Special	Performs operation defined in value1	See suboperations

Suboperations

Subopcode	Instruction	Operation
0	Syscall	OS syscall
1	Terminate	Terminate processor
2	Multiply	Multiply r(value1) and r(value2), store result in rHigh and rLow
3	Divide	Divide r(value1) and r(value2), store quotient in rHigh and remainder in rLow