Enter debugger when a VDP data port read would cause a CPU lockup

2 files changed, 15 insertions, 1 deletions

diff --git a/genesis.c b/genesis.c
index 7733f91..5cb010d 100644
--- a/genesis.c
+++ b/genesis.c
@@ -266,7 +266,7 @@ static void adjust_int_cycle(m68k_context * context, vdp_context * v_context)
 	}
 
 	context->target_cycle = context->int_cycle < context->sync_cycle ? context->int_cycle : context->sync_cycle;
-	if (context->should_return) {
+	if (context->should_return || gen->header.enter_debugger) {
 		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
diff --git a/vdp.c b/vdp.c
index 0ffc1a2..b0e412f 100644
--- a/vdp.c
+++ b/vdp.c
@@ -3953,6 +3953,20 @@ uint16_t vdp_data_port_read(vdp_context * context)
 	}
 	if (context->cd & 1) {
 		warning("Read from VDP data port while writes are configured, CPU is now frozen. VDP Address: %X, CD: %X\n", context->address, context->cd);
+		context->system->enter_debugger = 1;
+		return context->prefetch;
+	}
+	switch (context->cd)
+	{
+	case VRAM_READ:
+	case VSRAM_READ:
+	case CRAM_READ:
+	case VRAM_READ8:
+		break;
+	default:
+		warning("Read from VDP data port with invalid source, CPU is now frozen. VDP Address: %X, CD: %X\n", context->address, context->cd);
+		context->system->enter_debugger = 1;
+		return context->prefetch;
 	}
 	while (!(context->flags & FLAG_READ_FETCHED)) {
 		vdp_run_context_full(context, context->cycles + ((context->regs[REG_MODE_4] & BIT_H40) ? 16 : 20));