Instruction set completion project for a CPU with below features.
16-bit Instruction Word (IW) of ProjectCPU:
IW
|----------------------------------|
bit position |15 13 | 12 0|
|----------------------------------|
field name | opcode | A |
|----------------------------------|
bit width | 3b | 13b |
|----------------------------------|
(Every memory location and W are 16 bits)
Instruction Set of ProjectCPU:
ADD ->
unsigned Add
opcode = 0
W = W + (*A)
write(readFromAddress(A) +W) to W
*A = value (content of) address A = mem[A] (mem means memory)
= means write (assign)
NOR ->
bitwise NOR
opcode = 1
W = ~(W | (*A))
SRRL ->
Shift Rotate Right or Left
opcode = 2
if((*A) is less than 16) W = W >> (*A)
else if((*A) is between 16 and 31) W = W << lower4bits(*A)
else if((*A) is between 32 and 47) W = RotateRight W by lower4bits(*A)
else W = RotateLeft W by lower4bits(*A)
GT ->
Unsigned Greater Than
opcode = 3
W = W > (*A)
SZ ->
Skip on Zero
opcode = 4
PC = ((*A) == 0) ? (PC+2) : (PC+1)
CP2W ->
Copy to W
opcode = 5
W = *A
CPfW ->
Copy from W CPfW 0
opcode = 6
*A = W
JMP ->
Jump
opcode = 7
PC = lower13bits(*A)
INDIRECT ADRESSING
There are no special instructions for indirect addressing. Instead, every instruction can operate in indirect addressing mode.
That is, if A==0, replace *A above with **2.
Every program starts like this:
0: JMP 1
1: 3
2: // indirection register
3: // program actually starts here
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