#include "../../build/memory.inc"
#include "../../bios.inc"
#include "../../hardware.inc"

CTC_BASE        .equ 020h
CTC_CHANNEL_0   .equ CTC_BASE+000h
CTC_CHANNEL_1   .equ CTC_BASE+001h
CTC_CHANNEL_2   .equ CTC_BASE+002h
CTC_CHANNEL_3   .equ CTC_BASE+003h

RAM_TOP         .equ 0xbfff
; workspace variables here vv
; ------------------------ ^^
SAVED_SP        .equ RAM_TOP-0x02 ; word
STACK_TOP       .equ RAM_TOP-0x100

; -------------------------------------------------------
; Entry
; -------------------------------------------------------
.org SN76489_ROM_START
    push        bc
    push        de
    push        hl

    ld          hl, 0
    add         hl, sp              ; get sp
    ld          (SAVED_SP), hl      ; save sp for later
    ld          hl, STACK_TOP
    ld          sp, hl              ; use own stack

    ld          hl,str_header
    call        BIOS_PUTS

    ld          hl,SHARED_MEM_START+042h
    ld          bc, ctc_interrupt   ; install own ctc isr
    ld          (hl), bc

    di

    call        PSGInit             ; Initialize psglib
    ld          a,10100111b         ; interrupts enabled
                                    ; timer mode
                                    ; prescaler 256
                                    ; automatic trigger
                                    ; time constant follows
                                    ; reset
                                    ; control word
    out         (CTC_CHANNEL_1), a
    ld          a,78                ; 50Hz
    out         (CTC_CHANNEL_1), a

    ; music must be loaded from 8000
    ld          hl, 0x8000
    call        PSGPlayNoRepeat

    ei

exit:
    ld          hl, (SAVED_SP)
    ld          sp, hl              ; restore original stack

    pop         hl
    pop         de
    pop         bc
    ret

; -------------------------------------------------------
; CTC CHAN 1 interrupt handler
; -------------------------------------------------------
ctc_interrupt:
    push        af
    push        bc
    push        de
    push        hl

    call        PSGFrame

    pop         hl
    pop         de
    pop         bc
    pop         af
    reti

; -------------------------------------------------------
; Strings
; -------------------------------------------------------
str_header:     .db "SN76489 test",00dh,00ah,000h

#include "psglib_zasm.asm"