# HG changeset patch
# User Michael Pavone <pavone@retrodev.com>
# Date 1495252444 25200
# Node ID 30123ca5856ca99314afc0ddc05ebbb7a478a4fa
# Parent  df6af7187b36215dcb485c814cbb5f9f69924ab0
Added some code to try and prevent Z80 accesses and refresh cycles from screwing up interrupt latency more than on hardware

diff -r df6af7187b36 -r 30123ca5856c genesis.c
--- a/genesis.c	Fri May 19 20:27:35 2017 -0700
+++ b/genesis.c	Fri May 19 20:54:04 2017 -0700
@@ -96,6 +96,19 @@
 		//This can cause issues with the implementation of STOP though
 		context->target_cycle = context->current_cycle;
 	}
+	if (context->target_cycle == context->int_cycle) {
+		//Currently delays from Z80 access and refresh are applied only when we sync
+		//this can cause extra latency when it comes to interrupts
+		//to prevent this code forces some extra synchronization in the period immediately before an interrupt
+		if ((context->target_cycle - context->current_cycle) > gen->int_latency_prev1) {
+			context->target_cycle = context->sync_cycle = context->int_cycle - gen->int_latency_prev1;
+		} else if ((context->target_cycle - context->current_cycle) > gen->int_latency_prev2) {
+			context->target_cycle = context->sync_cycle = context->int_cycle - gen->int_latency_prev2;
+		} else {
+			context->target_cycle = context->sync_cycle = context->current_cycle;
+		}
+		
+	}
 	/*printf("Cyc: %d, Trgt: %d, Int Cyc: %d, Int: %d, Mask: %X, V: %d, H: %d, HICount: %d, HReg: %d, Line: %d\n",
 		context->current_cycle, context->target_cycle, context->int_cycle, context->int_num, (context->status & 0x7),
 		v_context->regs[REG_MODE_2] & 0x20, v_context->regs[REG_MODE_1] & 0x10, v_context->hint_counter, v_context->regs[REG_HINT], v_context->cycles / MCLKS_LINE);*/
@@ -1003,6 +1016,8 @@
 	gen->frame_end = vdp_cycles_to_frame_end(gen->vdp);
 	char * config_cycles = tern_find_path(config, "clocks\0max_cycles\0", TVAL_PTR).ptrval;
 	gen->max_cycles = config_cycles ? atoi(config_cycles) : DEFAULT_SYNC_INTERVAL;
+	gen->int_latency_prev1 = MCLKS_PER_68K * 32;
+	gen->int_latency_prev2 = MCLKS_PER_68K * 16;
 
 	char * lowpass_cutoff_str = tern_find_path(config, "audio\0lowpass_cutoff\0", TVAL_PTR).ptrval;
 	uint32_t lowpass_cutoff = lowpass_cutoff_str ? atoi(lowpass_cutoff_str) : DEFAULT_LOWPASS_CUTOFF;
diff -r df6af7187b36 -r 30123ca5856c genesis.h
--- a/genesis.h	Fri May 19 20:27:35 2017 -0700
+++ b/genesis.h	Fri May 19 20:54:04 2017 -0700
@@ -40,6 +40,8 @@
 	uint32_t        normal_clock; //Normal master clock (used to restore master clock after turbo mode)
 	uint32_t        frame_end;
 	uint32_t        max_cycles;
+	uint32_t        int_latency_prev1;
+	uint32_t        int_latency_prev2;
 	uint8_t         bank_regs[8];
 	uint16_t        mapper_start_index;
 	uint8_t         save_type;