111 lines
2.7 KiB
OCaml
111 lines
2.7 KiB
OCaml
open Printf
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(** http://bgb.bircd.org/pandocs.htm#cpuregistersandflags
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http://gameboy.mongenel.com/dmg/lesson1.html *)
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type registers = {
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mutable a : char; (* accumulator *)
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mutable f : char; (* flags *)
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mutable b : char;
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mutable c : char;
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mutable d : char;
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mutable e : char;
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mutable h : char;
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mutable l : char;
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mutable sp : int; (* stack pointer *)
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mutable pc : int; (* program counter *)
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}
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(* type flags = {
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z : bool; (* zero *)
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n : bool; (* substraction *)
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h : bool; (* half-carry *)
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cy : bool; (* carry *)
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} *)
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type t = {
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reg : registers;
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mutable cycles : int;
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}
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(** http://bgb.bircd.org/pandocs.htm#powerupsequence *)
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let init_registers =
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{
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a = '\x00';
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f = '\x00';
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b = '\x00';
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c = '\x00';
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d = '\x00';
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e = '\x00';
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h = '\x00';
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l = '\x00';
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sp = 0xFFFE;
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pc = 0x0100;
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}
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let init_cpu =
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{ reg = init_registers; cycles = 0 }
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let inc_pc cpu count =
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cpu.reg.pc <- cpu.reg.pc + count
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let inc_cycles cpu count =
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cpu.cycles <- cpu.cycles + count
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let merge_bytes low high =
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(int_of_char high) * 256 + (int_of_char low)
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let split_2B x =
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let low = x mod 256 |> char_of_int in
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let high = x / 256 |> char_of_int in
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(high, low)
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let read_2B b addr =
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let low = Bytes.get b addr in
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let high = Bytes.get b (addr + 1) in
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merge_bytes low high
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let inc_BC cpu =
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let v = merge_bytes cpu.reg.c cpu.reg.b in
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let low, high = split_2B (v + 1) in
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cpu.reg.c <- low;
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cpu.reg.b <- high
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(** http://imrannazar.com/GameBoy-Z80-Opcode-Map *)
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let run cpu (cartridge: Cartridge.t) =
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let data = cartridge.full_rom in
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let n = Bytes.get data (cpu.reg.pc + 1) in
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let nn = Bytes.get data (cpu.reg.pc + 2) in
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(* Hexa.print_slice cartridge.full_rom cpu.reg.pc (cpu.reg.pc + 7); *)
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match Bytes.get data cpu.reg.pc with
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| '\x00' -> printf " NOP\n";
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inc_pc cpu 1; inc_cycles cpu 4
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| '\x03' -> printf " INC \tBC\n";
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inc_BC cpu;
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inc_pc cpu 1; inc_cycles cpu 8
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| '\x3E' -> printf " LD \tA, 0x%02X\n" (int_of_char n);
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cpu.reg.a <- n;
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inc_pc cpu 2; inc_cycles cpu 8
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| '\xAF' -> printf " XOR \tA, A\n";
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let int_A = int_of_char cpu.reg.a in
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cpu.reg.a <- char_of_int @@ int_A lxor int_A;
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inc_pc cpu 1; inc_cycles cpu 4
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| '\xC3' -> let addr = read_2B data (cpu.reg.pc + 1) in
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printf " JP \t0x%04X\n" addr;
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cpu.reg.pc <- addr; inc_cycles cpu 16
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| '\xE0' -> printf " LDH \t(0x%02X), A\n" (int_of_char n);
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(* fixme *)
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inc_pc cpu 2; inc_cycles cpu 12
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| '\xF3' -> printf " DI\n";
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(* fixme *)
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inc_pc cpu 1; inc_cycles cpu 4
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| _ as x -> eprintf "opcode %02X\n" (int_of_char x); failwith "Unimplemented opcode."
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