Relay CPU Software Stack

.macro push 1
    st a ppm_save_a
    st b ppm_save_b
    st c ppm_save_c
    st d ppm_save_d

    st %1 ppm_sp_high

    ld b ppm_sp_low
    ldi c #-1
    add a
    st a ppm_sp_low

    ld a ppm_save_a
    ld b ppm_save_b
    ld c ppm_save_c
    ld d ppm_save_d
.endmacro

.macro pop 1
    st a ppm_save_a
    st b ppm_save_b
    st c ppm_save_c
    st d ppm_save_d

    ld b ppm_sp_low
    ldi c #1
    add a
    st a ppm_sp_low

    ld a ppm_sp_high
    st a ppm_load

    ld a ppm_save_a
    ld b ppm_save_b
    ld c ppm_save_c
    ld d ppm_save_d

    ld %1 ppm_load
.endmacro

jmp start

.resb 256

ppm_save_a: .resb 1
ppm_save_b: .resb 1
ppm_save_c: .resb 1
ppm_save_d: .resb 1
ppm_load: .resb 1
ppm_sp_high: .resb 1
ppm_sp_low: .db -1

start:  ldi a #1
        ldi b #2
        ldi c #3
        ldi d #4

        push a
        push b
        push c
        push d

        pop a
        pop b
        pop c
        pop d

        hlt