snes.snz

FUN cop [INTR] {}
FUN brk [INTR] {}
FUN irq [INTR] {}

FUN cop_emu [EMU, INTR] {}
FUN nmi_emu [EMU, INTR] {}
FUN irq_emu [EMU, INTR] {}

# Init code stolen shamelessly from
# https://en.wikibooks.org/wiki/Super_NES_Programming/Initialization_Tutorial/Snes_Init
FUN reset [EMU, INTR] {
  SEI;
  # No explicit switch to native mode - the [NAT] block handles that transition for us
  [NAT] {
    [WIDEM] {
      # Setup the stack and zero page pointers
      C := 0x01FF;
      S := C;
      C := 0x0000;
      D := C;
    }

    A := 0x8F;
    *0x2100 := A;
    *0x2101 := 0;
    *0x2102 := 0;
    *0x2103 := 0;
    *0x2105 := 0;
    *0x2106 := 0;
    *0x2107 := 0;
    *0x2108 := 0;
    *0x2109 := 0;
    *0x210A := 0;
    *0x210B := 0;
    *0x210C := 0;
    *0x210D := 0;
    *0x210D := 0;
    A := 0xFF;
    *0x210E := A;
    *0x2110 := A;
    *0x2112 := A;
    *0x2114 := A;
    A := 0x07;
    *0x210E := A;
    *0x2110 := A;
    *0x2112 := A;
    *0x2114 := A;
    *0x210f := 0;
    *0x210f := 0;
    *0x2111 := 0;
    *0x2111 := 0;
    *0x2113 := 0;
    *0x2113 := 0;
    A := 0x80;
    *0x2115 := A;
    *0x2116 := 0;
    *0x2117 := 0;
    *0x211A := 0;
    *0x211B := 0;
    A := 0x01;
    *0x211B := A;
    *0x211C := 0;
    *0x211C := 0;
    *0x211D := 0;
    *0x211D := 0;
    *0x211E := 0;
    *0x211E := A;
    *0x211F := 0;
    *0x211F := 0;
    *0x2120 := 0;
    *0x2120 := 0;
    *0x2121 := 0;
    *0x2123 := 0;
    *0x2124 := 0;
    *0x2125 := 0;
    *0x2126 := 0;
    *0x2127 := 0;
    *0x2128 := 0;
    *0x2129 := 0;
    *0x212A := 0;
    *0x212B := 0;
    *0x212C := A;
    *0x212D := 0;
    *0x212E := 0;
    *0x212F := 0;
    A := 0x30;
    *0x2130 := A;
    *0x2131 := 0;
    A := 0xE0;
    *0x2132 := A;
    *0x2133 := 0;

    A := 0xFF;
    *0x4200 := 0;
    *0x4201 := A;
    *0x4202 := 0;
    *0x4203 := 0;
    *0x4204 := 0;
    *0x4205 := 0;
    *0x4206 := 0;
    *0x4207 := 0;
    *0x4208 := 0;
    *0x4209 := 0;
    *0x420A := 0;
    *0x420B := 0;
    *0x420C := 0;
    *0x420D := 0;

    CLI;
    main();
  }
}

# END setup boilerplate

VAR inidisp := 0x2100;
VAR cgdata := 0x2122;
VAR nmitimen := 0x4200;
VAR status := 0x0000;

FUN main {
  # force-blanking is on from init, so we can set PPU registers

  # Load a nice dark blue into the palette.
  # cgaddr is already at address 0 from init
  A := 0x3C;
  cgdata := 0;
  cgdata := A;

  # TODO: Set our game state to its initial value

  # Our init is done - enable NMI for first gamestate update
  A := 2; # main loop done, NMI not done
  status := A; 

  # All startup done - enable NMI and auto joypad read
  A := 0x81;
  nmitimen := A;

  # Main Loop
  DO {
    # Wait for NMI 
    DO {
      A := status;
    } WHILE (A !& 1)

    # TODO: Update game state

    A := status;
    A |= 2; # Set "main loop done" bit
    A &= 0xFE; # Clear "NMI done" bit
    status := A;
  }
}

FUN nmi [INTR] {
  [WIDEM, WIDEX] {
    PUSH C;
    PUSH X;
    PUSH Y;
  }
  # Entering then leaving the WIDEM,WIDEX block above ensures we're in
  # narrow M,X here post-interrupt-entry
  
  # Check if game update is done
  A := status;
  IF (A && 2) {
    # Enable force blank
    A := 0x8F;
    inidisp := A;

    # TODO: Update PPU state for new game state

    # Disable force blank
    A := 0x0F;
    inidisp := A;

    # Signal to main loop that PPU is updated, and it can iterate again
    A := status;
    A |= 1; # Set "NMI done" bit
    A &= 0xFD; # Clear "main loop done" bit
    status := A;
  }

  [WIDEM, WIDEX] {
    POP Y;
    POP X;
    POP C;
  }
}