cpu32/INSTRUCTIONS.md

# RISC combined instruction set

goal: a semi-efficient insatruction set that offers few instructions that offer
the combined functions of conventional risc instuctions.

as such most instructions could be pipelined, I don't know how to feel about that

# Memory Operations
when accessing memory trough an address a consecutive pair of registers is used,
each consecutive pair of registers is given a name, for brevity a pair is 
always referred to as `A`. The possible pairs are:

- A = R1:R0
- B = R3:R2
- C = R5:R4
- D = R7:R6
- E = R9:R8
- F = R11:R10
- G = R13:R12
- H = R15:R14
- I = R17:R16
- J = R19:R18
- K = R21:R20
- L = R23:R22
- M = R25:R24
- N = R27:R26
- O = R29:R28
- P = R31:R30


## LD load value into register
post increment/decrement
syntax: `LD Rd, A+q`
action: `Rd = [A]; A += q`

pre increment/decrement
syntax: `LD Rd, q+A`
action: `A += q; Rd = [A]`

## LDI load immediate into register
syntax: `LDI Rd, imm`
action: `Rd = imm`

## LDIL load long immediate into register
syntax: `LDIL Rd, imm32`
action: `Rd = imm32`

## ST store value from register
post increment/decrement
syntax: `ST A+q, Rd`
action: `[A] = Rd; A += q`

pre increment/decrement
syntax: `ST q+A, Rd`
action: `A += q; [A] = Rd`

## STI store immediate into memory
post increment/decrement
syntax: `STI A+q, imm`
action: `[A] = imm; A += q`

pre increment/decrement
syntax: `STI q+A, imm`
action: `A += q; [A] = imm`

## STIL store long immediate into memory
post increment/decrement
syntax: `STIL A+q, imm32`
action: `[A] = imm32; A += q`

pre increment/decrement
syntax: `STIL q+A, imm32`
action: `A += q; [A] = imm32`


# Arithmetic operations

## ADD
## ADDC
## ADDI
## ADDIC

## MLA Multiply and add
syntax: `MLA A, Ra, Rb, Rc`
action: `A = Rc + (Ra * Rb)`

## MLAI Multiply and add immediate
syntax: `MLAI A, Ra, Rb, imm`
action: `A = imm + (Ra * Rb)`

## MLIA Multiply immediate and add
syntax: `MLIA A, Ra, imm, Rc`
action: `A = Rc + (Ra * imm)`

## MLAC Multiply and add with carry
syntax: `MLAC A, Ra, Rb, Rc`
action: `A = F.C + Rc + (Ra * Rb)`

## MLAIC Multiply and add immediate with carry
syntax: `MLAIC A, Ra, Rb, imm`
action: `A = F.C + imm + (Ra * Rb)`

## MLIAC Multiply immediate and add with carry
syntax: `MLIAC A, Ra, imm, Rc`
action: `A = F.C + Rc + (Ra * imm)`


## SMLA Signed multiply and add
syntax: `SMLA A, Ra, Rb, Rc`
action: `A = Rc + (Ra * Rb)`

## SMLAI Signed multiply and add immediate
syntax: `SMLAI A, Ra, Rb, imm`
action: `A = imm + (Ra * Rb)`

## SMLIA Signed multiply immediate and add
syntax: `SMLIA A, Ra, imm, Rc`
action: `A = Rc + (Ra * imm)`

## SMLAC Signed multiply and add with carry
syntax: `SMLAC A, Ra, Rb, Rc`
action: `A = F.C + Rc + (Ra * Rb)`

## SMLAIC Signed multiply and add immediate with carry
syntax: `SMLAIC A, Ra, Rb, imm`
action: `A = F.C + imm + (Ra * Rb)`

## SMLIAC Signed multiply immediate and add with carry
syntax: `SMLIAC A, Ra, imm, Rc`
action: `A = F.C + Rc + (Ra * imm)`


## SUB Subtract
## SUBC Subtract with carry
## SUBI Subtract immediate
## SBIC Subtract immediate with carry

## AND
## ANDI with immediate
## OR
## ORI with immediate
## XOR
## XORI with immediate

## NEG negate (two's complement)

## ROR Rotate right
## ROL Rotate left
## SHR Shift right
## SHRC Shift right through carry
## SHL Shift left
## SHLC Shift left through carry

# Conditional operations