From 1259ac4f6085ec3663fe96290b0d027da618a746 Mon Sep 17 00:00:00 2001
From: kub <derkub@gmail.com>
Date: Sun, 26 Jan 2020 20:46:21 +0100
Subject: [PATCH] VDP timing improvements

---
 pico/pico.c      |  3 ++-
 pico/pico_cmn.c  |  2 +-
 pico/pico_int.h  |  5 ++---
 pico/videoport.c | 10 ++++++----
 4 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/pico/pico.c b/pico/pico.c
index 2a16a0e2..b65b7de8 100644
--- a/pico/pico.c
+++ b/pico/pico.c
@@ -254,7 +254,7 @@ PICO_INTERNAL int CheckDMA(int cycles)
   dma_op1 = dma_op;
   if(Pico.video.reg[12] & 1) dma_op |= 4; // 40 cell mode?
   if(!(Pico.video.status&8)&&(Pico.video.reg[1]&0x40)) dma_op|=8; // active display?
-  xfers_can = (dma_timings[dma_op] * cycles + 0xff) >> 16;
+  xfers_can = (dma_timings[dma_op] * cycles + 0x8000) >> 16;
   if(xfers <= xfers_can)
   {
     Pico.video.status &= ~SR_DMA;
@@ -265,6 +265,7 @@ PICO_INTERNAL int CheckDMA(int cycles)
     if(!(dma_op&2)) burn = cycles;
     Pico.m.dma_xfers -= xfers_can;
   }
+  Pico.t.dma_end = SekCyclesDone() + burn;
 
   elprintf(EL_VDPDMA, "~Dma %i op=%i can=%i burn=%i [%u]",
     Pico.m.dma_xfers, dma_op1, xfers_can, burn, SekCyclesDone());
diff --git a/pico/pico_cmn.c b/pico/pico_cmn.c
index 8c22c977..b7e7d835 100644
--- a/pico/pico_cmn.c
+++ b/pico/pico_cmn.c
@@ -56,10 +56,10 @@ static void SekSyncM68k(void)
 static __inline void SekRunM68k(int cyc)
 {
   Pico.t.m68c_aim += cyc;
+  Pico.t.m68c_cnt += cyc >> 6; // refresh slowdowns
   cyc = Pico.t.m68c_aim - Pico.t.m68c_cnt;
   if (cyc <= 0)
     return;
-  Pico.t.m68c_cnt += cyc >> 6; // refresh slowdowns
   SekSyncM68k();
 }
 
diff --git a/pico/pico_int.h b/pico/pico_int.h
index a24fc6f6..357de4a9 100644
--- a/pico/pico_int.h
+++ b/pico/pico_int.h
@@ -137,9 +137,7 @@ extern m68ki_cpu_core PicoCpuMM68k, PicoCpuMS68k;
 
 // burn cycles while not in SekRun() and while in
 #define SekCyclesBurn(c)    Pico.t.m68c_cnt += c
-#define SekCyclesBurnRun(c) { \
-  SekCyclesLeft -= c; \
-}
+#define SekCyclesBurnRun(c) SekCyclesLeft -= c
 
 // note: sometimes may extend timeslice to delay an irq
 #define SekEndRun(after) { \
@@ -421,6 +419,7 @@ struct PicoTiming
   unsigned int z80c_aim;
   int z80_scanline;
 
+  unsigned int dma_end;                 // end of current DMA op (m68k cycles)
   int timer_a_next_oflow, timer_a_step; // in z80 cycles
   int timer_b_next_oflow, timer_b_step;
 };
diff --git a/pico/videoport.c b/pico/videoport.c
index c2fbd0ca..16a73119 100644
--- a/pico/videoport.c
+++ b/pico/videoport.c
@@ -376,12 +376,12 @@ PICO_INTERNAL_ASM void PicoVideoWrite(unsigned int a,unsigned short d)
       pvid->pending=0;
     }
 
-    if (!(pvid->status & SR_VB) && !(PicoIn.opt&POPT_DIS_VDP_FIFO))
+    if (!(pvid->status & SR_VB) && (pvid->reg[1]&0x40) && !(PicoIn.opt&POPT_DIS_VDP_FIFO))
     {
       int use = pvid->type == 1 ? 2 : 1;
       pvid->lwrite_cnt -= use;
       if (pvid->lwrite_cnt < 0)
-        SekCyclesLeft = 0;
+        SekCyclesBurnRun(488 - (SekCyclesDone()-Pico.t.m68c_line_start));
       elprintf(EL_ASVDP, "VDP data write: [%04x] %04x [%u] {%i} #%i @ %06x",
         Pico.video.addr, d, SekCyclesDone(), Pico.video.type, pvid->lwrite_cnt, SekPc);
     }
@@ -509,9 +509,11 @@ static u32 SrLow(const struct PicoVideo *pv)
 {
   unsigned int c, d = pv->status;
 
-  c = SekCyclesDone() - Pico.t.m68c_line_start - 39;
-  if (c < 92)
+  c = SekCyclesDone();
+  if (c - Pico.t.m68c_line_start - 39 < 92)
     d |= SR_HB;
+  if (CYCLES_GT(c, Pico.t.dma_end))
+    d &= ~SR_DMA;
   return d;
 }
 
-- 
2.39.5