Only do full sync on VDP data port reads instead of all VDP port reads, provides a perf bump for games that busy wait on the status or HV registers

1 files changed, 13 insertions, 11 deletions

diff --git a/genesis.c b/genesis.c
index 51d1a72..df35cc8 100644
--- a/genesis.c
+++ b/genesis.c
@@ -632,16 +632,27 @@ static uint16_t vdp_port_read(uint32_t vdp_port, m68k_context * context)
 	refresh_counter = refresh_counter % (MCLKS_PER_68K * REFRESH_INTERVAL);
 	last_sync_cycle = context->current_cycle;
 #endif
-	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) {
+			sync_components(context, 0);
+			uint32_t before_cycle = v_context->cycles;
 			value = vdp_data_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;
+				//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;
+			}
 		} else if(vdp_port < 8) {
+			vdp_run_context(v_context, context->current_cycle);
 			value = vdp_control_port_read(v_context);
 		} else {
+			vdp_run_context(v_context, context->current_cycle);
 			value = vdp_hv_counter_read(v_context);
 			//printf("HV Counter: %X at cycle %d\n", value, v_context->cycles);
 		}
@@ -650,15 +661,6 @@ static uint16_t vdp_port_read(uint32_t vdp_port, m68k_context * context)
 	} else {
 		value = get_open_bus_value(&gen->header);
 	}
-	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;
-		//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;
-	}
 #ifdef REFRESH_EMULATION
 	last_sync_cycle -= 4;
 	//refresh may have happened while we were waiting on the VDP,