atari7800: new presets; fixed indirect timing

presets/atari7800/wsync.c

@@ -0,0 +1,27 @@
+
+#include "atari7800.h"
+
+void main() {
+  byte y1 = 110;	// Y start of bar
+  byte y2 = 10;		// height of bar
+  byte i;
+  while (1) {
+    // wait for end of frame / start of vblank
+    while ((MARIA.MSTAT & MSTAT_VBLANK) == 0) ;
+    // wait for end of vblank / start of frame
+    while ((MARIA.MSTAT & MSTAT_VBLANK) != 0) ;
+    // skip scanlines until at top of bar
+    for (i=0; i<y1; i++) {
+      WSYNC();
+    }
+    // set the background color on each scanline
+    for (i=0; i<y2; i++) {
+      MARIA.BACKGRND = P6532.SWCHA - i;
+      WSYNC();
+    }
+    // clear the background after the final scanline
+    MARIA.BACKGRND = 0;
+    // move bar slowly downward
+    y1++;
+  }
+}

src/machine/atari7800.ts

@@ -191,7 +191,7 @@ class MARIA {
     this.cycles = 0;
     this.pixels.fill(this.regs[0x0]);
     if (this.isDMAEnabled()) {
-      this.cycles += 16;
+      this.cycles += 16; // TODO: last line in zone gets additional 8 cycles
       // time for a new DLL entry?
       if (this.offset < 0) {
         this.readDLLEntry(bus);
@@ -237,7 +237,10 @@ class MARIA {
           let data = this.readDMA( dbl ? (gfxadr+(i>>1)) : (gfxadr+i) );
           if (indirect) {
             let indadr = ((this.regs[0x14] + this.offset) << 8) + data;
-            if (dbl && (i&1)) indadr++;
+            if (dbl && (i&1)) {
+              indadr++;
+              this.cycles -= 3; // indirect read has 6/9 cycles
+            }
             data = this.readDMA(indadr);
           }
           // TODO: more modes

src/platform/atari7800.ts

@@ -5,6 +5,7 @@ import { PLATFORMS } from "../emu";
 
 var Atari7800_PRESETS = [
   {id:'sprites.dasm', name:'Sprites (ASM)'},
+  {id:'wsync.c', name:'WSYNC'},
 ];
 
 class Atari7800Platform extends Base6502MachinePlatform<Atari7800> implements Platform {