From e3c18cdf4b58062444f1781ae709618cbfcc9661 Mon Sep 17 00:00:00 2001
From: Scott Duensing <scott@kangaroopunch.com>
Date: Sun, 21 Jul 2024 19:25:51 -0500
Subject: [PATCH] Added DMA clear.  Almost working!

---
 src/main.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/src/main.c b/src/main.c
index 30419c1..da68494 100644
--- a/src/main.c
+++ b/src/main.c
@@ -146,6 +146,63 @@
 
 #include "a23d2.h"
 
+asm (
+  ".text\n"
+//  " .cpu mosw65c02\n"
+//  "mos-insns-w65c02\n"
+//  "EF_MOS_ARCH_W65C02 \n"
+  ".global dmaClear\n"
+  "dmaClear:\n"
+  "pha\n"
+//  "phx\n"
+  ".byte $DA\n"
+  "php          \n"  // preserver interrupt state + c
+  "sei          \n"  // disable interrupts
+  "ldy 1        \n"  // y = io_ctrl
+  //"phy          \n"  // save io_ctrl on stack
+  ".byte $5A\n"
+  //"stz 1        \n"  // map in the dma registers, where we can get them
+  ".byte $64,$01  \n"
+  //"stz $DF00    \n"  // clear dma control
+  ".byte $9c,$00,$DF\n"
+  "ldy #$05     \n"  // DMA_CTRL_ENABLE+DMA_CTRL_FILL
+  "sty $DF00    \n"
+  "ldy __rc8    \n"  // Fill Color
+  "sty $DF01    \n"  // Fill value
+  "sta $DF08    \n"  // Addr Low
+  "stx $DF09    \n"  // Addr Hi
+  "lda __rc2    \n"  // Addr Bank
+  "sta $DF0A    \n"
+  "lda __rc4    \n"  // length low
+  "sta $DF0C    \n"
+  "lda __rc5    \n"  // length middle
+  "sta $DF0D    \n"
+  "lda __rc6    \n"  // length high
+  "sta $DF0E    \n"
+  "lda #$80     \n"  // DMA_CTRL_START
+  //"tsb $DF00    \n"  // DMA_CTRL
+  ".byte $0C,$00,$DF\n"
+"wait:   lda $DF01    \n"  // DMA_STATUS
+  "bmi wait     \n"  // Wait for DMA
+ //"stz $DF00    \n"  // DMA Off
+  ".byte $9c,$00,$DF\n"
+  "nop          \n"
+  "nop          \n"
+  "nop          \n"  // wait
+  "nop          \n"
+  "nop          \n"
+  "nop          \n"
+  "pla          \n" // restore the io_ctrl
+  "sta 1        \n"
+  "plp          \n"
+//  "plx\n"
+  ".byte $FA\n"
+  "pla\n"
+  "rts          \n"
+);
+
+void dmaClear(uint32_t address, uint32_t length, byte color);
+
 
 #if 0
 typedef struct airplaneS {
@@ -346,6 +403,7 @@ float  collectZ = 0;
 
 
 
+
 // This flight model is basically the one from "Build Your Own Flight Sim
 // in C++" by Michael Radtke and Chris Lampton.
 void lightPlane(void) {
@@ -603,11 +661,17 @@ void runSimulation(void) {
 			_drawlist = DRAWLIST_P0;
 		}
 
+#if 0
 		// Erase old scene.
 		bitmapSetColor(0);
 		_useColor = false;
 		//textPrint("a23d2Draw()\n");
 		a23d2Draw();
+#else
+
+		dmaClear(pageZero ? 0x6c000 : 0x58000, 0x12c00, 0);
+
+#endif
 
 		// Draw new scene.
 		//textPrint("a23d2Render()\n");