From aa41c89e6841f2cc839af0074274c193b614efef Mon Sep 17 00:00:00 2001
From: Aaron Culliney <devnull@deadc0de.org>
Date: Sat, 7 Apr 2018 11:32:52 -0700
Subject: [PATCH] Lite refactor video timing

---
 src/audio/mockingboard.c |  5 +++-
 src/audio/speaker.c      |  4 ++-
 src/display.c            |  3 +--
 src/timing.c             | 54 ++++++++++------------------------------
 src/timing.h             | 27 +++++++++++++++++---
 5 files changed, 45 insertions(+), 48 deletions(-)

diff --git a/src/audio/mockingboard.c b/src/audio/mockingboard.c
index bba293b0..81e01d42 100644
--- a/src/audio/mockingboard.c
+++ b/src/audio/mockingboard.c
@@ -2368,7 +2368,7 @@ void MB_UpdateCycles(ULONG uExecutedCycles)
 	if(g_SoundcardType == CT_Empty)
 		return;
 
-	timing_checkpoint_cycles();
+	timing_checkpointCycles();
 	unsigned long uCycles = cycles_count_total - g_uLastCumulativeCycles;
 	g_uLastCumulativeCycles = cycles_count_total;
 #if MB_TRACING
@@ -2385,6 +2385,9 @@ void MB_UpdateCycles(ULONG uExecutedCycles)
 	_ASSERT(uCycles < 0x10000);
 #endif
 	uint16_t nClocks = (uint16_t) uCycles;
+        if (nClocks == 0) {
+            return;
+        }
 
 	for(int i=0; i<NUM_SY6522; i++)
 	{
diff --git a/src/audio/speaker.c b/src/audio/speaker.c
index a2cb9d1c..6444fadf 100644
--- a/src/audio/speaker.c
+++ b/src/audio/speaker.c
@@ -445,6 +445,8 @@ void speaker_flush(void) {
 
     ASSERT_ON_CPU_THREAD();
 
+    timing_checkpointCycles();
+
     if (is_fullspeed) {
         cycles_quiet_time = cycles_count_total;
         speaker_going_silent = false;
@@ -514,7 +516,7 @@ GLUE_C_READ(speaker_toggle)
 {
     ASSERT_ON_CPU_THREAD();
 
-    timing_checkpoint_cycles();
+    timing_checkpointCycles();
 
 #if SPEAKER_TRACING
     // output cycle count delta when toggled
diff --git a/src/display.c b/src/display.c
index afa2ebd7..6604f594 100644
--- a/src/display.c
+++ b/src/display.c
@@ -1377,7 +1377,6 @@ unsigned long video_clearDirty(unsigned long flags) {
 // References to Jim Sather's books are given as eg:
 // UTAIIe:5-7,P3 (Understanding the Apple IIe, chapter 5, page 7, Paragraph 3)
 
-extern unsigned int CpuGetCyclesThisVideoFrame(void);
 uint16_t video_scanner_get_address(bool *vblBarOut) {
     const bool SW_HIRES   = (run_args.softswitches & SS_HIRES);
     const bool SW_TEXT    = (run_args.softswitches & SS_TEXT);
@@ -1386,7 +1385,7 @@ uint16_t video_scanner_get_address(bool *vblBarOut) {
     const bool SW_MIXED   = (run_args.softswitches & SS_MIXED);
 
     // get video scanner position
-    unsigned int nCycles = CpuGetCyclesThisVideoFrame();
+    unsigned int nCycles = timing_currentVideoFrameCycles();
 
     // machine state switches
     int nHires   = (SW_HIRES && !SW_TEXT) ? 1 : 0;
diff --git a/src/timing.c b/src/timing.c
index 5d952221..8a14951e 100644
--- a/src/timing.c
+++ b/src/timing.c
@@ -9,28 +9,6 @@
  *
  */
 
-/*
- * 65c02 CPU timing support. Source inspired/derived from AppleWin.
- *
- * Simplified timing loop for each execution period:
- *
- * ..{...+....[....|..................|.........]....^....|....^....^....}......
- *  ti  MBB       CHK                CHK            MBE  CHX  SPK  MBX  tj   ZZZ
- *
- *      - ti  : timing sample begin (lock out interface thread)
- *      - tj  : timing sample end   (unlock interface thread)
- *      -  [  : cpu65_run()
- *      -  ]  : cpu65_run() finished
- *      - CHK : incoming timing_checkpoint_cycles() call from IO (bumps cycles_count_total)
- *      - CHX : update remainder of timing_checkpoint_cycles() for execution period
- *      - MBB : Mockingboard begin
- *      - MBE : Mockingboard end/flush (output)
- *      - MBX : Mockingboard end video frame (output)
- *      - SPK : Speaker output
- *      - ZZZ : housekeeping+sleep (or not)
- *
- */
-
 #include "common.h"
 
 #define DEBUG_TIMING (!defined(NDEBUG) && 0) // enable to print timing stats
@@ -42,18 +20,12 @@
 
 #define DISK_MOTOR_QUIET_NSECS 2000000
 
-// VBL constants?
-#define uCyclesPerLine 65 // 25 cycles of HBL & 40 cycles of HBL'
-#define uVisibleLinesPerFrame (64*3) // 192
-#define uLinesPerFrame (262) // 64 in each third of the screen & 70 in VBL
-#define dwClksPerFrame (uCyclesPerLine * uLinesPerFrame) // 17030
-
 // cycle counting
 double cycles_persec_target = CLK_6502;
 unsigned long cycles_count_total = 0;           // Running at spec ~1MHz, this will approach overflow in ~4000secs (for 32bit architectures)
 int cycles_speaker_feedback = 0;
 static int32_t cycles_checkpoint_count = 0;
-static unsigned int g_dwCyclesThisFrame = 0;
+static unsigned int cycles_this_frame = 0;
 
 // scaling and speed adjustments
 #if !MOBILE_DEVICE
@@ -144,7 +116,7 @@ void reinitialize(void) {
 #endif
 
     cycles_count_total = 0;
-    g_dwCyclesThisFrame = 0;
+    cycles_this_frame = 0;
 #if TESTING
     extern unsigned long (*testing_getCyclesCount)(void);
     if (testing_getCyclesCount) {
@@ -352,11 +324,11 @@ cpu_runloop:
 #if DEBUG_TIMING
                 dbg_cycles_executed += run_args.cpu65_cycle_count;
 #endif
-                g_dwCyclesThisFrame += run_args.cpu65_cycle_count;
+                cycles_this_frame += run_args.cpu65_cycle_count;
 
                 if (is_debugging) {
                     debugging_cycles -= run_args.cpu65_cycle_count;
-                    timing_checkpoint_cycles();
+                    timing_checkpointCycles();
 
                     if (c_debugger_should_break() || (debugging_cycles <= 0)) {
                         int err = 0;
@@ -380,12 +352,13 @@ cpu_runloop:
 
             MB_UpdateCycles();
 
-            timing_checkpoint_cycles();
+            timing_checkpointCycles();
 
             speaker_flush(); // play audio
 
-            if (g_dwCyclesThisFrame >= dwClksPerFrame) {
-                g_dwCyclesThisFrame -= dwClksPerFrame;
+            // video frame counter overflow ...
+            if (cycles_this_frame >= CYCLES_FRAME) {
+                cycles_this_frame -= CYCLES_FRAME;
                 MB_EndOfVideoFrame();
             }
 
@@ -536,15 +509,14 @@ void timing_stopCPU(void) {
     }
 }
 
-unsigned int CpuGetCyclesThisVideoFrame(void) {
+unsigned int timing_currentVideoFrameCycles(void) {
     ASSERT_ON_CPU_THREAD();
-
-    timing_checkpoint_cycles();
-    return g_dwCyclesThisFrame + cycles_checkpoint_count;
+    timing_checkpointCycles();
+    return cycles_this_frame + cycles_checkpoint_count;
 }
 
-// Called when an IO-reg is accessed & accurate global cycle count info is needed
-void timing_checkpoint_cycles(void) {
+// Called when accurate global cycle count info is needed
+void timing_checkpointCycles(void) {
     ASSERT_ON_CPU_THREAD();
 
     const int32_t d = run_args.cpu65_cycle_count - cycles_checkpoint_count;
diff --git a/src/timing.h b/src/timing.h
index 1ae684c6..5ac4d64a 100644
--- a/src/timing.h
+++ b/src/timing.h
@@ -33,7 +33,6 @@
 #define EXECUTION_PERIOD_NSECS 1000000UL // NANOSECONDS_PER_SECOND / EXECUTION_CHURN_RATE
 
 // timing values cribbed from AppleWin ... reference: Sather's _Understanding the Apple IIe_
-// TODO: revisit this if/when attempting to actually sync up VBL/VSYNC to actual device vsync
 
 // 14318181.81...
 #define _M14     (157500000.0 / 11.0)
@@ -43,6 +42,19 @@
 #define CLK_6502     ((_M14     * 65.0) / 912.0)
 #define CLK_6502_INT ((unsigned int)CLK_6502)
 
+// HBL & VBL constants
+// UtAIIe:3-13 "There are exactly 17030 (65 x 262) 6502 cycles in every television scan of an American Apple"
+#define CYCLES_HBL      25
+#define CYCLES_VIS_BEGIN CYCLES_HBL
+#define CYCLES_VIS      40
+#define CYCLES_SCANLINE (CYCLES_HBL + CYCLES_VIS)       // 65
+#define SCANLINES_VBL   70
+#define SCANLINES_MIX   (20*8)                          // 160
+#define SCANLINES_VIS   (64*3)                          // 192
+#define SCANLINES_VBL_BEGIN SCANLINES_VIS
+#define SCANLINES_FRAME (SCANLINES_VBL + SCANLINES_VIS) // 262
+#define CYCLES_FRAME    (CYCLES_SCANLINE * SCANLINES_FRAME) // 17030
+
 #define CPU_SCALE_SLOWEST 0.25
 #define CPU_SCALE_FASTEST_PIVOT 4.0
 #define CPU_SCALE_FASTEST (CPU_SCALE_FASTEST_PIVOT + 0.0625)
@@ -118,12 +130,21 @@ void cpu_resume(void);
  */
 bool cpu_isPaused(void);
 
+// ----------------------------------------------------------------------------
+// Video frame and IRQ fine-grained timing.
+
 /*
- * checkpoints current cycle count and updates total (for timing-dependent I/O)
+ * Get current cycles count within this video frame
  */
-void timing_checkpoint_cycles(void);
+unsigned int timing_currentVideoFrameCycles() CALL_ON_CPU_THREAD;
+
+/*
+ * Checkpoints current cycle count and updates total (for timing-dependent I/O)
+ */
+void timing_checkpointCycles(void) CALL_ON_CPU_THREAD;
 
 // ----------------------------------------------------------------------------
+// save/restore state
 
 bool timing_saveState(StateHelper_s *helper);