Small tweaks to timing of 68K/Z80 interactions based on latest tests

2 files changed, 7 insertions, 0 deletions

diff --git a/blastem.c b/blastem.c
index e4645eb..aaed215 100644
--- a/blastem.c
+++ b/blastem.c
@@ -473,6 +473,8 @@ 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) {
@@ -591,6 +593,8 @@ 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) {
diff --git a/z80_to_x86.c b/z80_to_x86.c
index 215a7cb..54f4c6e 100644
--- a/z80_to_x86.c
+++ b/z80_to_x86.c
@@ -2630,6 +2630,9 @@ void z80_clear_busreq(z80_context * context, uint32_t cycle)
 	z80_run(context, cycle);
 	context->busreq = 0;
 	context->busack = 0;
+	//there appears to be at least a 1 Z80 cycle delay between busreq
+	//being released and resumption of execution
+	context->current_cycle += context->options->gen.clock_divider;
 }
 
 uint8_t z80_get_busack(z80_context * context, uint32_t cycle)