Remove hacky post-DMA delay add proper pre-DMA delay based on logic analyzer capture. 512 color screen is a bit messed up but mostly works. Needs investigation

2 files changed, 4 insertions, 7 deletions

diff --git a/genesis.c b/genesis.c
index 1a9a374..8f7031c 100644
--- a/genesis.c
+++ b/genesis.c
@@ -296,12 +296,6 @@ static m68k_context * vdp_port_write(uint32_t vdp_port, m68k_context * context,
 							sync_components(context, 0);
 							gen->bus_busy = 0;
 						}
-						if (!(v_context->flags & FLAG_DMA_RUN)) {
-							//two more slots of delay are needed to kill sufficient sprite capacity in Overdrive
-							//TODO: Measure exact value with logic analyzer
-							vdp_run_context(v_context, v_context->cycles + 1);
-							vdp_run_context(v_context, v_context->cycles + 1);
-						}
 					}
 					
 					if (blocked < 0) {
diff --git a/vdp.c b/vdp.c
index f97f42e..51f767e 100644
--- a/vdp.c
+++ b/vdp.c
@@ -2482,13 +2482,16 @@ int vdp_control_port_write(vdp_context * context, uint16_t value)
 			//
 			if((context->regs[REG_DMASRC_H] & 0xC0) != 0x80) {
 				//DMA copy or 68K -> VDP, transfer starts immediately
-				context->flags |= FLAG_DMA_RUN;
 				context->dma_cd = context->cd;
 				//printf("DMA start (length: %X) at cycle %d, frame: %d, vcounter: %d, hslot: %d\n", (context->regs[REG_DMALEN_H] << 8) | context->regs[REG_DMALEN_L], context->cycles, context->frame, context->vcounter, context->hslot);
 				if (!(context->regs[REG_DMASRC_H] & 0x80)) {
 					//printf("DMA Address: %X, New CD: %X, Source: %X, Length: %X\n", context->address, context->cd, (context->regs[REG_DMASRC_H] << 17) | (context->regs[REG_DMASRC_M] << 9) | (context->regs[REG_DMASRC_L] << 1), context->regs[REG_DMALEN_H] << 8 | context->regs[REG_DMALEN_L]);
+					//68K -> VDP DMA takes 4 slots to actually start reading even though it acquires the bus immediately
+					vdp_run_context(context, context->cycles + 16 * ((context->regs[REG_MODE_2] & BIT_MODE_5) && (context->regs[REG_MODE_4] & BIT_H40) ? 4 : 5));
+					context->flags |= FLAG_DMA_RUN;
 					return 1;
 				} else {
+					context->flags |= FLAG_DMA_RUN;
 					//printf("DMA Copy Address: %X, New CD: %X, Source: %X\n", context->address, context->cd, (context->regs[REG_DMASRC_M] << 8) | context->regs[REG_DMASRC_L]);
 				}
 			} else {