From 702162215364848b4f7ebd86e7279437fdcd2f65 Mon Sep 17 00:00:00 2001
From: kub <derkub@gmail.com>
Date: Wed, 12 Jul 2023 22:35:33 +0200
Subject: [PATCH] core, fix z80 vcounter value

---
 pico/memory.c   |  2 +-
 pico/pico.c     |  9 +++++++++
 pico/pico_cmn.c | 35 ++++++++---------------------------
 pico/pico_int.h |  9 +++++++++
 4 files changed, 27 insertions(+), 28 deletions(-)

diff --git a/pico/memory.c b/pico/memory.c
index 2016f48d..96a00744 100644
--- a/pico/memory.c
+++ b/pico/memory.c
@@ -1367,7 +1367,7 @@ static unsigned char z80_md_vdp_read(unsigned short a)
       case 0x04: return PicoVideoRead8CtlH(1);
       case 0x05: return PicoVideoRead8CtlL(1);
       case 0x08:
-      case 0x0c: return get_scanline(1); // FIXME: make it proper
+      case 0x0c: return PicoVideoGetV(get_scanline(1));
       case 0x09:
       case 0x0d: return Pico.m.rotate++;
     }
diff --git a/pico/pico.c b/pico/pico.c
index 6b2124b3..ced4091e 100644
--- a/pico/pico.c
+++ b/pico/pico.c
@@ -225,6 +225,15 @@ void PicoLoopPrepare(void)
     // force setting possibly changed..
     Pico.m.pal = (PicoIn.regionOverride == 2 || PicoIn.regionOverride == 8) ? 1 : 0;
 
+  if (Pico.m.pal) {
+    Pico.t.vcnt_wrap = 0x103;
+    Pico.t.vcnt_adj = 57;
+  }
+  else {
+    Pico.t.vcnt_wrap = 0xEB;
+    Pico.t.vcnt_adj = 6;
+  }
+
   Pico.m.dirtyPal = 1;
   rendstatus_old = -1;
 
diff --git a/pico/pico_cmn.c b/pico/pico_cmn.c
index 40ce766e..a06573e1 100644
--- a/pico/pico_cmn.c
+++ b/pico/pico_cmn.c
@@ -136,7 +136,6 @@ static int PicoFrameHints(void)
 {
   struct PicoVideo *pv = &Pico.video;
   int lines, y, lines_vis, skip;
-  int vcnt_wrap, vcnt_adj;
   int hint; // Hint counter
 
   pevt_log_m68k_o(EVT_FRAME_START);
@@ -144,7 +143,6 @@ static int PicoFrameHints(void)
   skip = PicoIn.skipFrame;
 
   Pico.t.m68c_frame_start = Pico.t.m68c_aim;
-  pv->v_counter = Pico.m.scanline = 0;
   z80_resetCycles();
   PsndStartFrame();
 
@@ -153,16 +151,13 @@ static int PicoFrameHints(void)
   // === active display ===
   pv->status |= PVS_ACTIVE;
 
-  for (y = 0; ; y++)
+  for (y = 0;; y++)
   {
-    pv->v_counter = Pico.m.scanline = y;
-    if ((pv->reg[12]&6) == 6) { // interlace mode 2
-      pv->v_counter <<= 1;
-      pv->v_counter |= pv->v_counter >> 8;
-      pv->v_counter &= 0xff;
-    }
+    Pico.m.scanline = y;
+    pv->v_counter = PicoVideoGetV(y);
 
-    if ((y == 224 && !(pv->reg[1] & 8)) || y == 240)
+    lines_vis = (pv->reg[1] & 8) ? 240 : 224;
+    if (y == lines_vis)
       break;
 
     PAD_DELAY();
@@ -268,25 +263,11 @@ static int PicoFrameHints(void)
   pevt_log_m68k_o(EVT_NEXT_LINE);
 
   // === VBLANK ===
-  if (Pico.m.pal) {
-    lines = 313;
-    vcnt_wrap = 0x103;
-    vcnt_adj = 57;
-  }
-  else {
-    lines = 262;
-    vcnt_wrap = 0xEB;
-    vcnt_adj = 6;
-  }
-
+  lines = Pico.m.pal ? 313 : 262;
   for (y++; y < lines - 1; y++)
   {
-    pv->v_counter = Pico.m.scanline = y;
-    if (y >= vcnt_wrap)
-      pv->v_counter -= vcnt_adj;
-    if ((pv->reg[12]&6) == 6)
-      pv->v_counter = (pv->v_counter << 1) | 1;
-    pv->v_counter &= 0xff;
+    Pico.m.scanline = y;
+    pv->v_counter = PicoVideoGetV(y);
 
     PAD_DELAY();
 
diff --git a/pico/pico_int.h b/pico/pico_int.h
index d3229149..dc35426b 100644
--- a/pico/pico_int.h
+++ b/pico/pico_int.h
@@ -454,6 +454,8 @@ struct PicoTiming
 
   int timer_a_next_oflow, timer_a_step; // in z80 cycles
   int timer_b_next_oflow, timer_b_step;
+
+  int vcnt_wrap, vcnt_adj;
 };
 
 struct PicoSound
@@ -914,6 +916,13 @@ static __inline void VideoWriteVRAM(u32 a, u16 d)
     UpdateSAT(a, d);
 }
 
+static __inline u8 PicoVideoGetV(int scanline)
+{
+  if (scanline >= Pico.t.vcnt_wrap) scanline -= Pico.t.vcnt_adj;
+  if ((Pico.video.reg[12]&6) == 6) scanline = (scanline<<1) | 1;
+  return scanline;
+}
+
 PICO_INTERNAL_ASM void PicoVideoWrite(u32 a,unsigned short d);
 PICO_INTERNAL_ASM u32 PicoVideoRead(u32 a);
 unsigned char PicoVideoRead8DataH(int is_from_z80);
-- 
2.39.5