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diff blastem.c @ 508:b976c6d6e5fb

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Initial attempt at emulating extended bank area access delays when 68K bus is busy with VDP stuff. Also emulate the extra delay on the second access of a word-wide read to the bank area. Needs work as it seems to break stuff.
author Michael Pavone <pavone@retrodev.com>
date Mon, 03 Feb 2014 09:18:10 -0800
parents b7b7a1cab44a
children a277de8c1a18
line wrap: on
line diff
--- a/blastem.c	Tue Jan 28 08:36:06 2014 -0800
+++ b/blastem.c	Mon Feb 03 09:18:10 2014 -0800
@@ -312,10 +312,12 @@
 	//printf("vdp_port write: %X, value: %X, cycle: %d\n", vdp_port, value, context->current_cycle);
 	sync_components(context, 0);
 	vdp_context * v_context = context->video_context;
+	genesis_context * gen = context->system;
 	if (vdp_port < 0x10) {
 		int blocked;
 		uint32_t before_cycle = v_context->cycles;
 		if (vdp_port < 4) {
+			gen->bus_busy = 1;
 			while (vdp_data_port_write(v_context, value) < 0) {
 				while(v_context->flags & FLAG_DMA_RUN) {
 					vdp_run_dma_done(v_context, mclks_per_frame);
@@ -347,6 +349,7 @@
 				//context->current_cycle = v_context->cycles / MCLKS_PER_68K;
 			}
 		} else if(vdp_port < 8) {
+			gen->bus_busy = 1;
 			blocked = vdp_control_port_write(v_context, value);
 			if (blocked) {
 				while (blocked) {
@@ -394,12 +397,17 @@
 			context->current_cycle = v_context->cycles / MCLKS_PER_68K;
 		}
 	} else if (vdp_port < 0x18) {
-		genesis_context * gen = context->system;
 		sync_sound(gen, context->current_cycle * MCLKS_PER_68K);
 		psg_write(gen->psg, value);
 	} else {
 		//TODO: Implement undocumented test register(s)
 	}
+	if (gen->bus_busy)
+	{
+		//Lock the Z80 out of the bus until the VDP access is complete
+		sync_z80(gen->z80, v_context->cycles);
+		gen->bus_busy = 0;
+	}
 	return context;
 }