--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/genesis.c	Fri Dec 09 09:48:48 2016 -0800
@@ -0,0 +1,936 @@
+/*
+ Copyright 2013-2016 Michael Pavone
+ This file is part of BlastEm.
+ BlastEm is free software distributed under the terms of the GNU General Public License version 3 or greater. See COPYING for full license text.
+*/
+#include "genesis.h"
+#include "blastem.h"
+#include <stdlib.h>
+#include "render.h"
+#include "gst.h"
+#include "util.h"
+#define MCLKS_NTSC 53693175
+#define MCLKS_PAL  53203395
+
+uint32_t MCLKS_PER_68K;
+#define MCLKS_PER_YM  7
+#define MCLKS_PER_Z80 15
+#define MCLKS_PER_PSG (MCLKS_PER_Z80*16)
+#define DEFAULT_SYNC_INTERVAL MCLKS_LINE
+#define DEFAULT_LOWPASS_CUTOFF 3390
+
+//TODO: Figure out the exact value for this
+#define LINES_NTSC 262
+#define LINES_PAL 312
+
+#define MAX_SOUND_CYCLES 100000
+
+uint16_t *cart;
+uint16_t *ram;
+uint8_t z80_ram[Z80_RAM_BYTES];
+
+uint16_t read_dma_value(uint32_t address)
+{
+	//addresses here are word addresses (i.e. bit 0 corresponds to A1), so no need to do multiply by 2
+	uint16_t *ptr = get_native_pointer(address*2, (void **)genesis->m68k->mem_pointers, &genesis->m68k->options->gen);
+	if (ptr) {
+		return *ptr;
+	}
+	//TODO: Figure out what happens when you try to DMA from weird adresses like IO or banked Z80 area
+	return 0;
+}
+
+uint16_t get_open_bus_value()
+{
+	return read_dma_value(genesis->m68k->last_prefetch_address/2);
+}
+
+void adjust_int_cycle(m68k_context * context, vdp_context * v_context)
+{
+	//static int old_int_cycle = CYCLE_NEVER;
+	genesis_context *gen = context->system;
+	if (context->sync_cycle - context->current_cycle > gen->max_cycles) {
+		context->sync_cycle = context->current_cycle + gen->max_cycles;
+	}
+	context->int_cycle = CYCLE_NEVER;
+	if ((context->status & 0x7) < 6) {
+		uint32_t next_vint = vdp_next_vint(v_context);
+		if (next_vint != CYCLE_NEVER) {
+			context->int_cycle = next_vint;
+			context->int_num = 6;
+		}
+		if ((context->status & 0x7) < 4) {
+			uint32_t next_hint = vdp_next_hint(v_context);
+			if (next_hint != CYCLE_NEVER) {
+				next_hint = next_hint < context->current_cycle ? context->current_cycle : next_hint;
+				if (next_hint < context->int_cycle) {
+					context->int_cycle = next_hint;
+					context->int_num = 4;
+
+				}
+			}
+		}
+	}
+	if (context->int_cycle > context->current_cycle && context->int_pending == INT_PENDING_SR_CHANGE) {
+		context->int_pending = INT_PENDING_NONE;
+	}
+	/*if (context->int_cycle != old_int_cycle) {
+		printf("int cycle changed to: %d, level: %d @ %d(%d), frame: %d, vcounter: %d, hslot: %d, mask: %d, hint_counter: %d\n", context->int_cycle, context->int_num, v_context->cycles, context->current_cycle, v_context->frame, v_context->vcounter, v_context->hslot, context->status & 0x7, v_context->hint_counter);
+		old_int_cycle = context->int_cycle;
+	}*/
+
+	context->target_cycle = context->int_cycle < context->sync_cycle ? context->int_cycle : context->sync_cycle;
+	if (context->should_return) {
+		context->target_cycle = context->current_cycle;
+	} else if (context->target_cycle < context->current_cycle) {
+		//Changes to SR can result in an interrupt cycle that's in the past
+		//This can cause issues with the implementation of STOP though
+		context->target_cycle = context->current_cycle;
+	}
+	/*printf("Cyc: %d, Trgt: %d, Int Cyc: %d, Int: %d, Mask: %X, V: %d, H: %d, HICount: %d, HReg: %d, Line: %d\n",
+		context->current_cycle, context->target_cycle, context->int_cycle, context->int_num, (context->status & 0x7),
+		v_context->regs[REG_MODE_2] & 0x20, v_context->regs[REG_MODE_1] & 0x10, v_context->hint_counter, v_context->regs[REG_HINT], v_context->cycles / MCLKS_LINE);*/
+}
+
+//#define DO_DEBUG_PRINT
+#ifdef DO_DEBUG_PRINT
+#define dprintf printf
+#define dputs puts
+#else
+#define dprintf
+#define dputs
+#endif
+
+#define Z80_VINT_DURATION 128
+
+void z80_next_int_pulse(z80_context * z_context)
+{
+		genesis_context * gen = z_context->system;
+	z_context->int_pulse_start = vdp_next_vint_z80(gen->vdp);
+	z_context->int_pulse_end = z_context->int_pulse_start + Z80_VINT_DURATION * MCLKS_PER_Z80;
+			}
+
+void sync_z80(z80_context * z_context, uint32_t mclks)
+{
+#ifndef NO_Z80
+	if (z80_enabled) {
+		z80_run(z_context, mclks);
+	} else
+#endif
+	{
+		z_context->current_cycle = mclks;
+	}
+}
+
+void sync_sound(genesis_context * gen, uint32_t target)
+{
+	//printf("YM | Cycle: %d, bpos: %d, PSG | Cycle: %d, bpos: %d\n", gen->ym->current_cycle, gen->ym->buffer_pos, gen->psg->cycles, gen->psg->buffer_pos * 2);
+	while (target > gen->psg->cycles && target - gen->psg->cycles > MAX_SOUND_CYCLES) {
+		uint32_t cur_target = gen->psg->cycles + MAX_SOUND_CYCLES;
+		//printf("Running PSG to cycle %d\n", cur_target);
+		psg_run(gen->psg, cur_target);
+		//printf("Running YM-2612 to cycle %d\n", cur_target);
+		ym_run(gen->ym, cur_target);
+	}
+	psg_run(gen->psg, target);
+	ym_run(gen->ym, target);
+
+	//printf("Target: %d, YM bufferpos: %d, PSG bufferpos: %d\n", target, gen->ym->buffer_pos, gen->psg->buffer_pos * 2);
+}
+
+uint32_t last_frame_num;
+
+//My refresh emulation isn't currently good enough and causes more problems than it solves
+#ifdef REFRESH_EMULATION
+#define REFRESH_INTERVAL 128
+#define REFRESH_DELAY 2
+uint32_t last_sync_cycle;
+uint32_t refresh_counter;
+#endif
+
+m68k_context * sync_components(m68k_context * context, uint32_t address)
+{
+	genesis_context * gen = context->system;
+	vdp_context * v_context = gen->vdp;
+	z80_context * z_context = gen->z80;
+#ifdef REFRESH_EMULATION
+	//lame estimation of refresh cycle delay
+	if (!gen->bus_busy) {
+		refresh_counter += context->current_cycle - last_sync_cycle;
+		context->current_cycle += REFRESH_DELAY * MCLKS_PER_68K * (refresh_counter / (MCLKS_PER_68K * REFRESH_INTERVAL));
+		refresh_counter = refresh_counter % (MCLKS_PER_68K * REFRESH_INTERVAL);
+	}
+#endif
+
+	uint32_t mclks = context->current_cycle;
+	sync_z80(z_context, mclks);
+	sync_sound(gen, mclks);
+	vdp_run_context(v_context, mclks);
+	if (v_context->frame != last_frame_num) {
+		//printf("reached frame end %d | MCLK Cycles: %d, Target: %d, VDP cycles: %d, vcounter: %d, hslot: %d\n", last_frame_num, mclks, gen->frame_end, v_context->cycles, v_context->vcounter, v_context->hslot);
+		last_frame_num = v_context->frame;
+
+		if(exit_after){
+			--exit_after;
+			if (!exit_after) {
+				exit(0);
+			}
+		}
+
+		vdp_adjust_cycles(v_context, mclks);
+		io_adjust_cycles(gen->ports, context->current_cycle, mclks);
+		io_adjust_cycles(gen->ports+1, context->current_cycle, mclks);
+		io_adjust_cycles(gen->ports+2, context->current_cycle, mclks);
+		context->current_cycle -= mclks;
+		z80_adjust_cycles(z_context, mclks);
+		gen->ym->current_cycle -= mclks;
+		gen->psg->cycles -= mclks;
+		if (gen->ym->write_cycle != CYCLE_NEVER) {
+			gen->ym->write_cycle = gen->ym->write_cycle >= mclks ? gen->ym->write_cycle - mclks : 0;
+		}
+	}
+	gen->frame_end = vdp_cycles_to_frame_end(v_context);
+	context->sync_cycle = gen->frame_end;
+	//printf("Set sync cycle to: %d @ %d, vcounter: %d, hslot: %d\n", context->sync_cycle, context->current_cycle, v_context->vcounter, v_context->hslot);
+	if (context->int_ack) {
+		//printf("acknowledging %d @ %d:%d, vcounter: %d, hslot: %d\n", context->int_ack, context->current_cycle, v_context->cycles, v_context->vcounter, v_context->hslot);
+		vdp_int_ack(v_context);
+		context->int_ack = 0;
+	}
+	if (!address && (break_on_sync || gen->save_state)) {
+		context->sync_cycle = context->current_cycle + 1;
+	}
+	adjust_int_cycle(context, v_context);
+	if (address) {
+		if (break_on_sync) {
+			break_on_sync = 0;
+			debugger(context, address);
+		}
+		if (gen->save_state && (z_context->pc || (!z_context->reset && !z_context->busreq))) {
+			uint8_t slot = gen->save_state - 1;
+			gen->save_state = 0;
+			//advance Z80 core to the start of an instruction
+			while (!z_context->pc)
+			{
+				sync_z80(z_context, z_context->current_cycle + MCLKS_PER_Z80);
+			}
+			char *save_path;
+			if (slot == QUICK_SAVE_SLOT) {
+				save_path = save_state_path;
+			} else {
+				char slotname[] = "slot_0.gst";
+				slotname[5] = '0' + slot;
+				char const *parts[] = {gen->save_dir, PATH_SEP, slotname};
+				save_path = alloc_concat_m(3, parts);
+			}
+			save_gst(gen, save_path, address);
+			printf("Saved state to %s\n", save_path);
+			if (slot != QUICK_SAVE_SLOT) {
+				free(save_path);
+			}
+		} else if(gen->save_state) {
+			context->sync_cycle = context->current_cycle + 1;
+		}
+	}
+#ifdef REFRESH_EMULATION
+	last_sync_cycle = context->current_cycle;
+#endif
+	return context;
+}
+
+m68k_context * vdp_port_write(uint32_t vdp_port, m68k_context * context, uint16_t value)
+{
+	if (vdp_port & 0x2700E0) {
+		fatal_error("machine freeze due to write to address %X\n", 0xC00000 | vdp_port);
+	}
+	vdp_port &= 0x1F;
+	//printf("vdp_port write: %X, value: %X, cycle: %d\n", vdp_port, value, context->current_cycle);
+	sync_components(context, 0);
+	genesis_context * gen = context->system;
+	vdp_context *v_context = gen->vdp;
+	if (vdp_port < 0x10) {
+		int blocked;
+		uint32_t before_cycle = v_context->cycles;
+		if (vdp_port < 4) {
+
+			while (vdp_data_port_write(v_context, value) < 0) {
+				while(v_context->flags & FLAG_DMA_RUN) {
+					vdp_run_dma_done(v_context, gen->frame_end);
+					if (v_context->cycles >= gen->frame_end) {
+						uint32_t cycle_diff = v_context->cycles - context->current_cycle;
+						uint32_t m68k_cycle_diff = (cycle_diff / MCLKS_PER_68K) * MCLKS_PER_68K;
+						if (m68k_cycle_diff < cycle_diff) {
+							m68k_cycle_diff += MCLKS_PER_68K;
+						}
+						context->current_cycle += m68k_cycle_diff;
+						gen->bus_busy = 1;
+						sync_components(context, 0);
+						gen->bus_busy = 0;
+					}
+				}
+				//context->current_cycle = v_context->cycles;
+			}
+		} else if(vdp_port < 8) {
+			blocked = vdp_control_port_write(v_context, value);
+			if (blocked) {
+				while (blocked) {
+					while(v_context->flags & FLAG_DMA_RUN) {
+						vdp_run_dma_done(v_context, gen->frame_end);
+						if (v_context->cycles >= gen->frame_end) {
+							uint32_t cycle_diff = v_context->cycles - context->current_cycle;
+							uint32_t m68k_cycle_diff = (cycle_diff / MCLKS_PER_68K) * MCLKS_PER_68K;
+							if (m68k_cycle_diff < cycle_diff) {
+								m68k_cycle_diff += MCLKS_PER_68K;
+							}
+							context->current_cycle += m68k_cycle_diff;
+							gen->bus_busy = 1;
+							sync_components(context, 0);
+							gen->bus_busy = 0;
+						}
+						if (!(v_context->flags & FLAG_DMA_RUN)) {
+							//two more slots of delay are needed to kill sufficient sprite capacity in Overdrive
+							//TODO: Measure exact value with logic analyzer
+							vdp_run_context(v_context, v_context->cycles + 1);
+							vdp_run_context(v_context, v_context->cycles + 1);
+						}
+					}
+					
+					if (blocked < 0) {
+						blocked = vdp_control_port_write(v_context, value);
+					} else {
+						blocked = 0;
+					}
+				}
+			} else {
+				context->sync_cycle = gen->frame_end = vdp_cycles_to_frame_end(v_context);
+				//printf("Set sync cycle to: %d @ %d, vcounter: %d, hslot: %d\n", context->sync_cycle, context->current_cycle, v_context->vcounter, v_context->hslot);
+				adjust_int_cycle(context, v_context);
+			}
+		} else {
+			fatal_error("Illegal write to HV Counter port %X\n", vdp_port);
+		}
+		if (v_context->cycles != before_cycle) {
+			//printf("68K paused for %d (%d) cycles at cycle %d (%d) for write\n", v_context->cycles - context->current_cycle, v_context->cycles - before_cycle, context->current_cycle, before_cycle);
+			uint32_t cycle_diff = v_context->cycles - context->current_cycle;
+			uint32_t m68k_cycle_diff = (cycle_diff / MCLKS_PER_68K) * MCLKS_PER_68K;
+			if (m68k_cycle_diff < cycle_diff) {
+				m68k_cycle_diff += MCLKS_PER_68K;
+			}
+			context->current_cycle += m68k_cycle_diff;
+#ifdef REFRESH_EMULATION
+			last_sync_cycle = context->current_cycle;
+#endif
+			//Lock the Z80 out of the bus until the VDP access is complete
+			gen->bus_busy = 1;
+			sync_z80(gen->z80, v_context->cycles);
+			gen->bus_busy = 0;
+		}
+	} else if (vdp_port < 0x18) {
+		psg_write(gen->psg, value);
+	} else {
+		//TODO: Implement undocumented test register(s)
+	}
+	return context;
+}
+
+m68k_context * vdp_port_write_b(uint32_t vdp_port, m68k_context * context, uint8_t value)
+{
+	return vdp_port_write(vdp_port, context, vdp_port < 0x10 ? value | value << 8 : ((vdp_port & 1) ? value : 0));
+}
+
+void * z80_vdp_port_write(uint32_t vdp_port, void * vcontext, uint8_t value)
+{
+	z80_context * context = vcontext;
+	genesis_context * gen = context->system;
+	vdp_port &= 0xFF;
+	if (vdp_port & 0xE0) {
+		fatal_error("machine freeze due to write to Z80 address %X\n", 0x7F00 | vdp_port);
+	}
+	if (vdp_port < 0x10) {
+		//These probably won't currently interact well with the 68K accessing the VDP
+		vdp_run_context(gen->vdp, context->current_cycle);
+		if (vdp_port < 4) {
+			vdp_data_port_write(gen->vdp, value << 8 | value);
+		} else if (vdp_port < 8) {
+			vdp_control_port_write(gen->vdp, value << 8 | value);
+		} else {
+			fatal_error("Illegal write to HV Counter port %X\n", vdp_port);
+		}
+	} else if (vdp_port < 0x18) {
+		sync_sound(gen, context->current_cycle);
+		psg_write(gen->psg, value);
+	} else {
+		vdp_test_port_write(gen->vdp, value);
+	}
+	return context;
+}
+
+uint16_t vdp_port_read(uint32_t vdp_port, m68k_context * context)
+{
+	if (vdp_port & 0x2700E0) {
+		fatal_error("machine freeze due to read from address %X\n", 0xC00000 | vdp_port);
+	}
+	vdp_port &= 0x1F;
+	uint16_t value;
+	sync_components(context, 0);
+	genesis_context *gen = context->system;
+	vdp_context * v_context = gen->vdp;
+	uint32_t before_cycle = v_context->cycles;
+	if (vdp_port < 0x10) {
+		if (vdp_port < 4) {
+			value = vdp_data_port_read(v_context);
+		} else if(vdp_port < 8) {
+			value = vdp_control_port_read(v_context);
+		} else {
+			value = vdp_hv_counter_read(v_context);
+			//printf("HV Counter: %X at cycle %d\n", value, v_context->cycles);
+		}
+	} else if (vdp_port < 0x18){
+		fatal_error("Illegal read from PSG  port %X\n", vdp_port);
+	} else {
+		value = vdp_test_port_read(v_context);
+	}
+	if (v_context->cycles != before_cycle) {
+		//printf("68K paused for %d (%d) cycles at cycle %d (%d) for read\n", v_context->cycles - context->current_cycle, v_context->cycles - before_cycle, context->current_cycle, before_cycle);
+		context->current_cycle = v_context->cycles;
+#ifdef REFRES_EMULATION
+		last_sync_cycle = context->current_cycle;
+#endif
+		//Lock the Z80 out of the bus until the VDP access is complete
+		genesis_context *gen = context->system;
+		gen->bus_busy = 1;
+		sync_z80(gen->z80, v_context->cycles);
+		gen->bus_busy = 0;
+	}
+	return value;
+}
+
+uint8_t vdp_port_read_b(uint32_t vdp_port, m68k_context * context)
+{
+	uint16_t value = vdp_port_read(vdp_port, context);
+	if (vdp_port & 1) {
+		return value;
+	} else {
+		return value >> 8;
+	}
+}
+
+uint8_t z80_vdp_port_read(uint32_t vdp_port, void * vcontext)
+{
+	z80_context * context = vcontext;
+	if (vdp_port & 0xE0) {
+		fatal_error("machine freeze due to read from Z80 address %X\n", 0x7F00 | vdp_port);
+	}
+	genesis_context * gen = context->system;
+	//VDP access goes over the 68K bus like a bank area access
+	//typical delay from bus arbitration
+	context->current_cycle += 3 * MCLKS_PER_Z80;
+	//TODO: add cycle for an access right after a previous one
+	//TODO: Below cycle time is an estimate based on the time between 68K !BG goes low and Z80 !MREQ goes high
+	//      Needs a new logic analyzer capture to get the actual delay on the 68K side
+	gen->m68k->current_cycle += 8 * MCLKS_PER_68K;
+
+
+	vdp_port &= 0x1F;
+	uint16_t ret;
+	if (vdp_port < 0x10) {
+		//These probably won't currently interact well with the 68K accessing the VDP
+		vdp_run_context(gen->vdp, context->current_cycle);
+		if (vdp_port < 4) {
+			ret = vdp_data_port_read(gen->vdp);
+		} else if (vdp_port < 8) {
+			ret = vdp_control_port_read(gen->vdp);
+		} else {
+			fatal_error("Illegal write to HV Counter port %X\n", vdp_port);
+		}
+	} else {
+		//TODO: Figure out the correct value today
+		ret = 0xFFFF;
+	}
+	return vdp_port & 1 ? ret : ret >> 8;
+}
+
+uint32_t zram_counter = 0;
+
+m68k_context * io_write(uint32_t location, m68k_context * context, uint8_t value)
+{
+	genesis_context * gen = context->system;
+	if (location < 0x10000) {
+		//Access to Z80 memory incurs a one 68K cycle wait state
+		context->current_cycle += MCLKS_PER_68K;
+		if (!z80_enabled || z80_get_busack(gen->z80, context->current_cycle)) {
+			location &= 0x7FFF;
+			if (location < 0x4000) {
+				z80_ram[location & 0x1FFF] = value;
+#ifndef NO_Z80
+				z80_handle_code_write(location & 0x1FFF, gen->z80);
+#endif
+			} else if (location < 0x6000) {
+				sync_sound(gen, context->current_cycle);
+				if (location & 1) {
+					ym_data_write(gen->ym, value);
+				} else if(location & 2) {
+					ym_address_write_part2(gen->ym, value);
+				} else {
+					ym_address_write_part1(gen->ym, value);
+				}
+			} else if (location == 0x6000) {
+				gen->z80->bank_reg = (gen->z80->bank_reg >> 1 | value << 8) & 0x1FF;
+				if (gen->z80->bank_reg < 0x80) {
+					gen->z80->mem_pointers[1] = (gen->z80->bank_reg << 15) + ((char *)gen->z80->mem_pointers[2]);
+				} else {
+					gen->z80->mem_pointers[1] = NULL;
+				}
+			} else {
+				fatal_error("68K write to unhandled Z80 address %X\n", location);
+			}
+		}
+	} else {
+		location &= 0x1FFF;
+		if (location < 0x100) {
+			switch(location/2)
+			{
+			case 0x1:
+				io_data_write(gen->ports, value, context->current_cycle);
+				break;
+			case 0x2:
+				io_data_write(gen->ports+1, value, context->current_cycle);
+				break;
+			case 0x3:
+				io_data_write(gen->ports+2, value, context->current_cycle);
+				break;
+			case 0x4:
+				gen->ports[0].control = value;
+				break;
+			case 0x5:
+				gen->ports[1].control = value;
+				break;
+			case 0x6:
+				gen->ports[2].control = value;
+				break;
+			}
+		} else {
+			if (location == 0x1100) {
+				if (value & 1) {
+					dputs("bus requesting Z80");
+					if (z80_enabled) {
+						z80_assert_busreq(gen->z80, context->current_cycle);
+					} else {
+						gen->z80->busack = 1;
+					}
+				} else {
+					if (gen->z80->busreq) {
+						dputs("releasing z80 bus");
+						#ifdef DO_DEBUG_PRINT
+						char fname[20];
+						sprintf(fname, "zram-%d", zram_counter++);
+						FILE * f = fopen(fname, "wb");
+						fwrite(z80_ram, 1, sizeof(z80_ram), f);
+						fclose(f);
+						#endif
+					}
+					if (z80_enabled) {
+						z80_clear_busreq(gen->z80, context->current_cycle);
+					} else {
+						gen->z80->busack = 0;
+					}
+				}
+			} else if (location == 0x1200) {
+				sync_z80(gen->z80, context->current_cycle);
+				if (value & 1) {
+					if (z80_enabled) {
+						z80_clear_reset(gen->z80, context->current_cycle);
+					} else {
+						gen->z80->reset = 0;
+					}
+				} else {
+					if (z80_enabled) {
+						z80_assert_reset(gen->z80, context->current_cycle);
+					} else {
+						gen->z80->reset = 1;
+					}
+				}
+			}
+		}
+	}
+	return context;
+}
+
+m68k_context * io_write_w(uint32_t location, m68k_context * context, uint16_t value)
+{
+	if (location < 0x10000 || (location & 0x1FFF) >= 0x100) {
+		return io_write(location, context, value >> 8);
+	} else {
+		return io_write(location, context, value);
+	}
+}
+
+#define FOREIGN 0x80
+#define HZ50 0x40
+#define USA FOREIGN
+#define JAP 0x00
+#define EUR (HZ50|FOREIGN)
+#define NO_DISK 0x20
+
+uint8_t io_read(uint32_t location, m68k_context * context)
+{
+	uint8_t value;
+	genesis_context *gen = context->system;
+	if (location < 0x10000) {
+		//Access to Z80 memory incurs a one 68K cycle wait state
+		context->current_cycle += MCLKS_PER_68K;
+		if (!z80_enabled || z80_get_busack(gen->z80, context->current_cycle)) {
+			location &= 0x7FFF;
+			if (location < 0x4000) {
+				value = z80_ram[location & 0x1FFF];
+			} else if (location < 0x6000) {
+				sync_sound(gen, context->current_cycle);
+				value = ym_read_status(gen->ym);
+			} else {
+				value = 0xFF;
+			}
+		} else {
+			value = 0xFF;
+		}
+	} else {
+		location &= 0x1FFF;
+		if (location < 0x100) {
+			switch(location/2)
+			{
+			case 0x0:
+				//version bits should be 0 for now since we're not emulating TMSS
+				value = gen->version_reg;
+				break;
+			case 0x1:
+				value = io_data_read(gen->ports, context->current_cycle);
+				break;
+			case 0x2:
+				value = io_data_read(gen->ports+1, context->current_cycle);
+				break;
+			case 0x3:
+				value = io_data_read(gen->ports+2, context->current_cycle);
+				break;
+			case 0x4:
+				value = gen->ports[0].control;
+				break;
+			case 0x5:
+				value = gen->ports[1].control;
+				break;
+			case 0x6:
+				value = gen->ports[2].control;
+				break;
+			default:
+				value = 0xFF;
+			}
+		} else {
+			if (location == 0x1100) {
+				value = z80_enabled ? !z80_get_busack(gen->z80, context->current_cycle) : !gen->z80->busack;
+				value |= (get_open_bus_value() >> 8) & 0xFE;
+				dprintf("Byte read of BUSREQ returned %d @ %d (reset: %d)\n", value, context->current_cycle, gen->z80->reset);
+			} else if (location == 0x1200) {
+				value = !gen->z80->reset;
+			} else {
+				value = 0xFF;
+				printf("Byte read of unknown IO location: %X\n", location);
+			}
+		}
+	}
+	return value;
+}
+
+uint16_t io_read_w(uint32_t location, m68k_context * context)
+{
+	uint16_t value = io_read(location, context);
+	if (location < 0x10000 || (location & 0x1FFF) < 0x100) {
+		value = value | (value << 8);
+	} else {
+		value <<= 8;
+		value |= get_open_bus_value() & 0xFF;
+	}
+	return value;
+}
+
+void * z80_write_ym(uint32_t location, void * vcontext, uint8_t value)
+{
+	z80_context * context = vcontext;
+	genesis_context * gen = context->system;
+	sync_sound(gen, context->current_cycle);
+	if (location & 1) {
+		ym_data_write(gen->ym, value);
+	} else if (location & 2) {
+		ym_address_write_part2(gen->ym, value);
+	} else {
+		ym_address_write_part1(gen->ym, value);
+	}
+	return context;
+}
+
+uint8_t z80_read_ym(uint32_t location, void * vcontext)
+{
+	z80_context * context = vcontext;
+	genesis_context * gen = context->system;
+	sync_sound(gen, context->current_cycle);
+	return ym_read_status(gen->ym);
+}
+
+uint8_t z80_read_bank(uint32_t location, void * vcontext)
+{
+	z80_context * context = vcontext;
+	genesis_context *gen = context->system;
+	if (gen->bus_busy) {
+		context->current_cycle = context->sync_cycle;
+	}
+	//typical delay from bus arbitration
+	context->current_cycle += 3 * MCLKS_PER_Z80;
+	//TODO: add cycle for an access right after a previous one
+	//TODO: Below cycle time is an estimate based on the time between 68K !BG goes low and Z80 !MREQ goes high
+	//      Needs a new logic analyzer capture to get the actual delay on the 68K side
+	gen->m68k->current_cycle += 8 * MCLKS_PER_68K;
+
+	location &= 0x7FFF;
+	if (context->mem_pointers[1]) {
+		return context->mem_pointers[1][location ^ 1];
+	}
+	uint32_t address = context->bank_reg << 15 | location;
+	if (address >= 0xC00000 && address < 0xE00000) {
+		return z80_vdp_port_read(location & 0xFF, context);
+	} else {
+		fprintf(stderr, "Unhandled read by Z80 from address %X through banked memory area (%X)\n", address, context->bank_reg << 15);
+	}
+	return 0;
+}
+
+void *z80_write_bank(uint32_t location, void * vcontext, uint8_t value)
+{
+	z80_context * context = vcontext;
+	genesis_context *gen = context->system;
+	if (gen->bus_busy) {
+		context->current_cycle = context->sync_cycle;
+	}
+	//typical delay from bus arbitration
+	context->current_cycle += 3 * MCLKS_PER_Z80;
+	//TODO: add cycle for an access right after a previous one
+	//TODO: Below cycle time is an estimate based on the time between 68K !BG goes low and Z80 !MREQ goes high
+	//      Needs a new logic analyzer capture to get the actual delay on the 68K side
+	gen->m68k->current_cycle += 8 * MCLKS_PER_68K;
+
+	location &= 0x7FFF;
+	uint32_t address = context->bank_reg << 15 | location;
+	if (address >= 0xE00000) {
+		address &= 0xFFFF;
+		((uint8_t *)ram)[address ^ 1] = value;
+	} else if (address >= 0xC00000) {
+		z80_vdp_port_write(location & 0xFF, context, value);
+	} else {
+		fprintf(stderr, "Unhandled write by Z80 to address %X through banked memory area\n", address);
+	}
+	return context;
+}
+
+void *z80_write_bank_reg(uint32_t location, void * vcontext, uint8_t value)
+{
+	z80_context * context = vcontext;
+
+	context->bank_reg = (context->bank_reg >> 1 | value << 8) & 0x1FF;
+	if (context->bank_reg < 0x100) {
+		genesis_context *gen = context->system;
+		context->mem_pointers[1] = get_native_pointer(context->bank_reg << 15, (void **)gen->m68k->mem_pointers, &gen->m68k->options->gen);
+	} else {
+		context->mem_pointers[1] = NULL;
+	}
+
+	return context;
+}
+
+void set_speed_percent(genesis_context * context, uint32_t percent)
+{
+	uint32_t old_clock = context->master_clock;
+	context->master_clock = ((uint64_t)context->normal_clock * (uint64_t)percent) / 100;
+	while (context->ym->current_cycle != context->psg->cycles) {
+		sync_sound(context, context->psg->cycles + MCLKS_PER_PSG);
+}
+	ym_adjust_master_clock(context->ym, context->master_clock);
+	psg_adjust_master_clock(context->psg, context->master_clock);
+}
+
+void set_region(genesis_context *gen, rom_info *info, uint8_t region)
+{
+	if (!region) {
+		char * def_region = tern_find_ptr(config, "default_region");
+		if (def_region && (!info->regions || (info->regions & translate_region_char(toupper(*def_region))))) {
+			region = translate_region_char(toupper(*def_region));
+		} else {
+			region = info->regions;
+		}
+	}
+	if (region & REGION_E) {
+		gen->version_reg = NO_DISK | EUR;
+	} else if (region & REGION_J) {
+		gen->version_reg = NO_DISK | JAP;
+	} else {
+		gen->version_reg = NO_DISK | USA;
+	}
+	
+	if (region & HZ50) {
+		gen->normal_clock = MCLKS_PAL;
+	} else {
+		gen->normal_clock = MCLKS_NTSC;
+	}
+	gen->master_clock = gen->normal_clock;
+}
+
+genesis_context *alloc_init_genesis(rom_info *rom, void *main_rom, void *lock_on, uint32_t ym_opts, uint8_t force_region)
+{
+	static memmap_chunk z80_map[] = {
+		{ 0x0000, 0x4000,  0x1FFF, 0, 0, MMAP_READ | MMAP_WRITE | MMAP_CODE, NULL, NULL, NULL, NULL,              NULL },
+		{ 0x8000, 0x10000, 0x7FFF, 0, 0, 0,                                  NULL, NULL, NULL, z80_read_bank,     z80_write_bank},
+		{ 0x4000, 0x6000,  0x0003, 0, 0, 0,                                  NULL, NULL, NULL, z80_read_ym,       z80_write_ym},
+		{ 0x6000, 0x6100,  0xFFFF, 0, 0, 0,                                  NULL, NULL, NULL, NULL,              z80_write_bank_reg},
+		{ 0x7F00, 0x8000,  0x00FF, 0, 0, 0,                                  NULL, NULL, NULL, z80_vdp_port_read, z80_vdp_port_write}
+	};
+	genesis_context *gen = calloc(1, sizeof(genesis_context));
+	set_region(gen, rom, force_region);
+
+	gen->vdp = malloc(sizeof(vdp_context));
+	init_vdp_context(gen->vdp, gen->version_reg & 0x40);
+	gen->frame_end = vdp_cycles_to_frame_end(gen->vdp);
+	char * config_cycles = tern_find_path(config, "clocks\0max_cycles\0").ptrval;
+	gen->max_cycles = config_cycles ? atoi(config_cycles) : DEFAULT_SYNC_INTERVAL;
+
+	char * lowpass_cutoff_str = tern_find_path(config, "audio\0lowpass_cutoff\0").ptrval;
+	uint32_t lowpass_cutoff = lowpass_cutoff_str ? atoi(lowpass_cutoff_str) : DEFAULT_LOWPASS_CUTOFF;
+	
+	gen->ym = malloc(sizeof(ym2612_context));
+	ym_init(gen->ym, render_sample_rate(), gen->master_clock, MCLKS_PER_YM, render_audio_buffer(), ym_opts, lowpass_cutoff);
+
+	gen->psg = malloc(sizeof(psg_context));
+	psg_init(gen->psg, render_sample_rate(), gen->master_clock, MCLKS_PER_PSG, render_audio_buffer(), lowpass_cutoff);
+
+	gen->z80 = calloc(1, sizeof(z80_context));
+	z80_map[0].buffer = gen->zram = calloc(1, Z80_RAM_BYTES);
+#ifndef NO_Z80
+	z80_options *z_opts = malloc(sizeof(z80_options));
+	init_z80_opts(z_opts, z80_map, 5, NULL, 0, MCLKS_PER_Z80);
+	init_z80_context(gen->z80, z_opts);
+	z80_assert_reset(gen->z80, 0);
+#endif
+
+	gen->z80->system = gen;
+	gen->z80->mem_pointers[0] = gen->zram;
+	gen->z80->mem_pointers[1] = gen->z80->mem_pointers[2] = (uint8_t *)cart;
+
+	gen->cart = main_rom;
+	gen->lock_on = lock_on;
+	gen->work_ram = calloc(2, RAM_WORDS);
+	gen->zram = z80_ram;
+	setup_io_devices(config, rom, gen);
+
+	gen->save_type = rom->save_type;
+	gen->save_type = rom->save_type;
+	if (gen->save_type != SAVE_NONE) {
+		gen->save_ram_mask = rom->save_mask;
+		gen->save_size = rom->save_size;
+		gen->save_storage = rom->save_buffer;
+		gen->eeprom_map = rom->eeprom_map;
+		gen->num_eeprom = rom->num_eeprom;
+		if (gen->save_type == SAVE_I2C) {
+			eeprom_init(&gen->eeprom, gen->save_storage, gen->save_size);
+		}
+	} else {
+		gen->save_storage = NULL;
+	}
+	
+	for (int i = 0; i < rom->map_chunks; i++)
+	{
+		if (rom->map[i].flags & MMAP_PTR_IDX) {
+			gen->m68k->mem_pointers[rom->map[i].ptr_index] = rom->map[i].buffer;
+		}
+		if (rom->map[i].start == 0xE00000) {
+			rom->map[i].buffer = gen->work_ram;
+		}
+	}
+
+	m68k_options *opts = malloc(sizeof(m68k_options));
+	init_m68k_opts(opts, rom->map, rom->map_chunks, MCLKS_PER_68K);
+	//TODO: make this configurable
+	opts->gen.flags |= M68K_OPT_BROKEN_READ_MODIFY;
+	gen->m68k = init_68k_context(opts, NULL);
+	gen->m68k->system = gen;
+
+	return gen;
+}
+
+
+
+void free_genesis(genesis_context *gen)
+{
+	vdp_free(gen->vdp);
+	m68k_options_free(gen->m68k->options);
+	free(gen->m68k);
+	free(gen->work_ram);
+	z80_options_free(gen->z80->options);
+	free(gen->z80);
+	free(gen->zram);
+	ym_free(gen->ym);
+	psg_free(gen->psg);
+	free(gen->save_storage);
+	free(gen->save_dir);
+	free(gen->lock_on);
+}
+
+void start_genesis(genesis_context *gen, char *statefile, uint8_t *debugger)
+{
+
+	if (statefile) {
+		uint32_t pc = load_gst(gen, statefile);
+		if (!pc) {
+			fatal_error("Failed to load save state %s\n", statefile);
+		}
+		printf("Loaded %s\n", statefile);
+		if (debugger) {
+			insert_breakpoint(gen->m68k, pc, debugger);
+		}
+		adjust_int_cycle(gen->m68k, gen->vdp);
+		start_68k_context(gen->m68k, pc);
+	} else {
+		if (debugger) {
+			uint32_t address = cart[2] << 16 | cart[3];
+			insert_breakpoint(gen->m68k, address, debugger);
+		}
+		m68k_reset(gen->m68k);
+	}
+}
+
+genesis_context *alloc_config_genesis(void *rom, uint32_t rom_size, void *lock_on, uint32_t lock_on_size, uint32_t ym_opts, uint8_t force_region, rom_info *info_out)
+{
+	static memmap_chunk base_map[] = {
+		{0xE00000, 0x1000000, 0xFFFF,   0, 0, MMAP_READ | MMAP_WRITE | MMAP_CODE, NULL,
+		           NULL,          NULL,         NULL,            NULL},
+		{0xC00000, 0xE00000,  0x1FFFFF, 0, 0, 0,                                  NULL,
+		           (read_16_fun)vdp_port_read,  (write_16_fun)vdp_port_write,
+		           (read_8_fun)vdp_port_read_b, (write_8_fun)vdp_port_write_b},
+		{0xA00000, 0xA12000,  0x1FFFF,  0, 0, 0,                                  NULL,
+		           (read_16_fun)io_read_w,      (write_16_fun)io_write_w,
+		           (read_8_fun)io_read,         (write_8_fun)io_write}
+	};
+	static tern_node *rom_db;
+	if (!rom_db) {
+		rom_db = load_rom_db();
+	}
+	*info_out = configure_rom(rom_db, rom, rom_size, lock_on, lock_on_size, base_map, sizeof(base_map)/sizeof(base_map[0]));
+#ifndef BIG_ENDIAN
+	byteswap_rom(rom, rom_size);
+	if (lock_on) {
+		byteswap_rom(lock_on, lock_on_size);
+	}
+#endif
+	char *m68k_divider = tern_find_path(config, "clocks\0m68k_divider\0").ptrval;
+	if (!m68k_divider) {
+		m68k_divider = "7";
+	}
+	MCLKS_PER_68K = atoi(m68k_divider);
+	if (!MCLKS_PER_68K) {
+		MCLKS_PER_68K = 7;
+	}
+	return alloc_init_genesis(info_out, rom, lock_on, ym_opts, force_region);
+}