sda4: commit the Glaze developer hard-drive dump

Un-ignored: the dev drive is the ground truth the restoration and
emulator work constantly reference (DPL3/LIBDPL + VRENDER i860 renderer
source, BT/RP live+dev game trees, VGL_LABS pod boot, scene/audio
content). Kept in-repo for the pod-owner community.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

sda4/DPL3/VRENDER/DMA.TXT

@@ -0,0 +1,63 @@
+
+To render a scene using the dma engine -
+
+
+void renderScene()
+{
+  start_up_frame();
+  tile=0;
+
+
+  scan_convert(tile, 0);
+
+  /* now wait for 1 interrupt from DMA engine */
+
+  tile++;
+
+  while (tile < tiles_in_frame) {
+    scan_convert(tile, 1);
+    /*
+       now wait for 2 interrupts from DMA engine, from scan-converter
+       and from end-of-texture
+     */
+    VRAMwritetoFrameStore(tile);
+    tile++;
+  }
+
+  scan_convert ( -1, 1 );
+  /*
+     again wait for 2 interrupts from DMA engine, 1 of which
+     appears real soon since there are no triangles in the NULL image!
+   */
+  VRAMwritetoFrameStore(tile);
+
+  /*
+    and we know that the last tile is at the bottom-right
+    of the screen, so we can flip frames at any point from here
+  */
+}
+
+The sync point is the end of texture() AND end of scan_convert().
+How do i organise this sync? The tranny needs to see 2 events (is there a
+race condition potentially in the event hardware?) before walking to the
+next tile. The code for 'texture tile' needs to do the end-of-frame code
+up to and including the VRAMwrite(), then GOTO scan-convert (next tile).
+
+The trick is to move the end-of-frame code to the BEGINNING of each tile.
+So tile 0 doesnt execute any end-of-frame code (achieved via a jump). All
+other tiles begin by executing the end-of-frame code for the previous
+tile. The end-of-frame code consists of
+
+
+    computing a 24-bit pixel from intrinsic
+    moving all variables into eof area
+    perspective divide
+    put texture address into bits 0..31
+    VRAMwrite (for texture lookup)
+    configure EMC's to new tileXY
+    clear out scan-converting area
+    start scan-converting polygons
+
+
+
+