About#
The SPU (or Simple Processing Unit) is a small custom 16-bit CPU I made inspired by the famous 6502.
The main goal of this CPU is to be the easiest CPU to use. The SPU have only 16 instructions as follows:
SPU Instruction Set#
| Instruction | Argument | What it does |
|---|---|---|
| ADD | None | Do X + Y and return the value to X. |
| SUB | None | Do X - Y and return the value to X. |
| AND | None | Do X & Y and return the value to X. |
| OR | None | Do X or Y and return the value to X. |
| XOR | None | Do X ^ Y and return the value to X. |
| NOT | None | Inverse the X register. |
| LDX | im12/adr12 | Change the value of X. |
| LDY | im12/adr12 | Change the value of Y. |
| STX | adr12 | Store the X register to the ram address. |
| STY | adr12 | Store the Y register to the ram address. |
| JMP | adr12 | Jump to the label/address. |
| JIC | adr12 | Jump to the label/address if the carry flag is set. |
| JIZ | adr12 | Jump to the label/address if the zero flag is set. |
| HLT | None | Stops the proccessor. |
I made an Assembler in Rust and made the full CPU circuit in Logisim Evolution. I didn’t made an emulator beacause I was too lazy… But it was a cool project to make.
Here is an exemple program witch do the fibonacci sequence:
/*
Do the fibonacci sequence.
The end result goes into the ram address $0001.
*/
;Init variables
ldx 0
stx $0001 ; prev1 = 0
ldx 1
stx $0002 ; prev2 = 1
ldx 9
stx $0000 ; n = 9
loop:
ldy 3
sub
ldy 128
add
jic stop ; if n < 3 { stop(); }
ldx $0002
ldy $0001
add
sty $0002 ; prev2 = prev1
stx $0001 ; prev1 = prev2 + prev1
ldx $0000
ldy 1
sub
stx $0000 ; n -= 1
jmp loop
stop:
hlt
For the frenchies I made a video about how I made the assembler:
Assembler repo#
Killarexe/SPU-Assembler
An assembler for the SPU using rust
Rust
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