Approximation of refresh wait states

1 files changed, 12 insertions, 2 deletions

diff --git a/blastem.c b/blastem.c
index 5691ebe..dc978f1 100644
--- a/blastem.c
+++ b/blastem.c
@@ -230,12 +230,21 @@ void sync_sound(genesis_context * gen, uint32_t target)
 	//printf("Target: %d, YM bufferpos: %d, PSG bufferpos: %d\n", target, gen->ym->buffer_pos, gen->psg->buffer_pos * 2);
 }
 
+#define REFRESH_INTERVAL 130
+#define REFRESH_DELAY 2
 uint32_t last_frame_num;
+uint32_t last_sync_cycle;
+uint32_t refresh_counter;
 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;
+	//lame estimation of refresh cycle delay
+	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);
+
 	uint32_t mclks = context->current_cycle;
 	sync_z80(z_context, mclks);
 	sync_sound(gen, mclks);
@@ -295,6 +304,7 @@ m68k_context * sync_components(m68k_context * context, uint32_t address)
 			context->sync_cycle = context->current_cycle + 1;
 		}
 	}
+	last_sync_cycle = context->current_cycle;
 	return context;
 }
 
@@ -354,7 +364,7 @@ m68k_context * vdp_port_write(uint32_t vdp_port, m68k_context * context, uint16_
 		}
 		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);
-			context->current_cycle = v_context->cycles;
+			last_sync_cycle = context->current_cycle = v_context->cycles;
 			//Lock the Z80 out of the bus until the VDP access is complete
 			gen->bus_busy = 1;
 			sync_z80(gen->z80, v_context->cycles);
@@ -427,7 +437,7 @@ uint16_t vdp_port_read(uint32_t vdp_port, m68k_context * 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;
+		last_sync_cycle = context->current_cycle = v_context->cycles;
 		//Lock the Z80 out of the bus until the VDP access is complete
 		genesis_context *gen = context->system;
 		gen->bus_busy = 1;