From: kub <derkub@gmail.com>
Date: Thu, 27 Jun 2024 22:20:31 +0000 (+0200)
Subject: core vdp, some cleanup
X-Git-Tag: v2.00~22
X-Git-Url: https://notaz.gp2x.de/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c1812e1a85f2c396bd162c93f629bc1db38050f2;p=picodrive.git

core vdp, some cleanup
---

diff --git a/pico/draw.c b/pico/draw.c
index 7c170baf..95b82b19 100644
--- a/pico/draw.c
+++ b/pico/draw.c
@@ -2125,7 +2125,6 @@ void PicoDrawSync(int to, int off, int on)
   {
     int width2 = (est->Pico->video.reg[12]&1) ? 160 : 128;
 
-    // technically, VDP starts active display output at slot 12
     if (unlikely(on|off) && (off >= width2 ||
           // hack for timing inaccuracy, if on/off near borders
           (off && off <= 24) || (on < width2 && on >= width2-24)))
@@ -2178,7 +2177,7 @@ void PicoDrawBgcDMA(u16 *base, u32 source, u32 mask, int dlen, int sl)
   BgcDMAoffs = 0;
 
   // handle slot offset in 1st line
-  if (sl-12 > 0) // active display output only starts at slot 12
+  if (sl-12 > 0)
     BgcDMAoffs = 2*(sl-12);
   else if (sl < 0) { // DMA starts before active display
     BgcDMAsrc += 2*-sl;
diff --git a/pico/videoport.c b/pico/videoport.c
index 79ee508d..462e4703 100644
--- a/pico/videoport.c
+++ b/pico/videoport.c
@@ -24,7 +24,7 @@ enum { clkdiv = 2 };    // CPU clock granularity: one of 1,2,4,8
 // One scanline is 63.7us/64.3us (ntsc/pal) long which is ~488.57 68k cycles.
 // Approximate by 488 for VDP.
 // 1 slot is 20/7 = 2.857 68k cycles in h32, and 16/7 = 2.286 in h40. That's
-// 171 slots in h32, and ~213.8 (really 193 plus 17 prolonged in HSYNC) in h40.
+// 171 slots in h32, and ~214 (really 193 plus 17 prolonged in HSYNC) in h40.
 enum { slcpu = 488 };
 
 // VDP has a slot counter running from 0x00 to 0xff every scanline, but it has
@@ -35,6 +35,11 @@ enum { slcpu = 488 };
 enum { hint32 = 0x85, gapstart32 = 0x94, gapend32 = 0xe9};
 enum { hint40 = 0xa5, gapstart40 = 0xb7, gapend40 = 0xe5};
 
+// Basic timing in h32: 38 slots (~108.5 cycles) from hint to VDP output start
+// at slot 0x00. vint takes place on the 1st VBLANK line in slot 0x01 (~111.5).
+// Rendering takes 128 slots (~365.5), and right border starts at slot 0x80
+// (~474 cycles). hint occurs after 5 slots into the border (~488.5 cycles).
+
 // The horizontal sync period (HBLANK) is 30/37 slots (h32/h40):
 // h32: 4 slots front porch (1.49us), 13 HSYNC (4.84us), 13 back porch (4.84us)
 // h40: 5 slots front porch (1.49us), 16 HSYNC (4.77us), 16 back porch (4.77us)
@@ -621,7 +626,7 @@ static void DmaSlow(int len, u32 source)
         if (sl > VdpFIFO.fifo_hcounts[0]-5) // hint delay is 5 slots
           sl = (s8)sl;
         // TODO this is needed to cover timing inaccuracies
-        if (sl <= 12)  sl = -2;
+        if (sl <= 12) sl = -2;
         PicoDrawBgcDMA(base, source, mask, len, sl);
         // do last DMA cycle since it's all going to the same cram location
         source = source+len-1;