// assembler: bass v17
// command: `bass -o gb-test.gb gb-test.bass.txt`

architecture gb.cpu

// Jump to any arbitrary location in ROM
macro seek(variable bank, variable offset) {
  origin (bank * $4000) + (offset % $4000)
  base offset
}

// Calls code in another bank
macro farcall(variable bank, variable location) {
	ld a, bank
	ld hl, location
	rst 00h
}

// Attempt to define some WRAM variables
namespace wram {
	variable i = $c000 // start here

	constant current_bank = i;i=i+ 1 // current_bank is 1 bytes long
	constant test_var = i;i=i+  2 // test_var is 2 bytes long
	// etc.
}

namespace hram {
	variable i = $ff80 // start here

	constant buffer = i;i=i+ 1 // buffer is 1 bytes long
	// etc.
}

namespace hardware {
	constant rombank = $2000
}

///////// home bank ///////////////

namespace home {
// interrupt and rst's
	seek(0, $00); jp Bankswitch // rst 00
	seek(0, $08); reti // rst 08
	seek(0, $10); reti // rst 10
	seek(0, $18); reti // rst 18
	seek(0, $20); reti // rst 20
	seek(0, $28); reti // rst 28
	seek(0, $30); reti // rst 30
	seek(0, $38); reti // rst 38
	seek(0, $40); jp VBlank // VBlank
	seek(0, $48); reti // LCDC
	seek(0, $50); reti // Timer
	seek(0, $58); reti // Serial
	seek(0, $60); reti // HiLo

// header
	seek(0, $100)
	nop
	jp Init // jump to init

// nintendo logo
	db $CE,$ED,$66,$66,$CC,$0D,$00,$0B,$03,$73,$00,$83,$00,$0C,$00,$0D
	db $00,$08,$11,$1F,$88,$89,$00,$0E,$DC,$CC,$6E,$E6,$DD,$DD,$D9,$99
	db $BB,$BB,$67,$63,$6E,$0E,$EC,$CC,$DD,$DC,$99,$9F,$BB,$B9,$33,$3E

// meta
	db "TEST ROM       " // title
	db $00 // cgb enabled
	db "ZU" // new licensee code
	db $00 // sgb enable
	db $12 // cart type
	db $00 // rom size
	db $00 // ram size
	db $01 // international
	db $33 // use new code
	db $00 // rom version
	db 0   // header chksum (use another tool?)
	dw 0   // global chksum (use another tool?)

// routines
	function Init {
	// which bank is loaded by default
		ld a, 1
		ld (wram.current_bank),a
	// do stuff
		call bank1.routine
	purgatory:
		halt
		nop
		jr purgatory
	}

	function VBlank {
		reti
	}

	// a = bank
	// hl = location
	function Bankswitch {
		ldh ((hram.buffer & $ff)),a // take the low byte of hram.buffer
		ld a,(wram.current_bank)
		push af
			ldh a,((hram.buffer & $ff))
			ld (wram.current_bank),a
			ld (hardware.rombank),a
			call +
		pop af
		ld (wram.current_bank),a
		ld (hardware.rombank),a
		ret
	+;	jp hl

	}
}

///////// bank 1 ///////////////

seek(1, $4000); namespace bank1 {
	function routine {
		farcall(2, bank2.routine)
		ret
	}
}

///////// bank 2 ///////////////

seek(2, $4000); namespace bank2 {
	function routine {
		variable x = 0
		ld a, 0
		while (x < 5) {
			ld (wram.test_var),a
			inc a
			x = x+1
		}
		ret
	}
}