From d81cbb56073061cc5b3fb9dfe578e846e34c059a Mon Sep 17 00:00:00 2001
From: Jorj Bauer <jorj@jorj.org>
Date: Mon, 28 Dec 2020 16:04:57 -0500
Subject: [PATCH] avoid fast-forwarding the CPU after exiting the BIOS

---
 sdl/aiie.cpp      |  8 +++++---
 teensy/teensy.ino | 14 ++++++++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/sdl/aiie.cpp b/sdl/aiie.cpp
index a2d3a22..04ba5c4 100644
--- a/sdl/aiie.cpp
+++ b/sdl/aiie.cpp
@@ -36,6 +36,8 @@ volatile bool wantResume = false;
 
 volatile bool cpuDebuggerRunning = false;
 
+volatile bool cpuClockInitialized = false;
+
 void doDebugging();
 void readPrefs();
 void writePrefs();
@@ -118,14 +120,13 @@ static struct timespec runBIOS(struct timespec now)
 
 static struct timespec runCPU(struct timespec now)
 {
-  static bool initialized = false;
   static struct timespec startTime;
   static struct timespec nextInstructionTime;
   
-  if (!initialized) {
+  if (!cpuClockInitialized) {
     do_gettime(&startTime);
     do_gettime(&nextInstructionTime);
-    initialized = true;
+    cpuClockInitialized = true;
   }
 
   // Check for interrupt-like actions before running the CPU
@@ -337,6 +338,7 @@ void loop()
       g_display->redraw(); // Redraw the UI
       ((AppleDisplay*)(g_vm->vmdisplay))->modeChange(); // force a full re-draw	and blit
 
+      cpuClockInitialized = false; // force it to reset so it doesn't fast-forward
       wasBios = false;
     }
   }
diff --git a/teensy/teensy.ino b/teensy/teensy.ino
index 53dd688..18e3ab8 100644
--- a/teensy/teensy.ino
+++ b/teensy/teensy.ino
@@ -41,6 +41,8 @@ TeensyUSB usb;
 
 Bounce resetButtonDebouncer = Bounce();
 
+volatile bool cpuClockInitialized = false;
+
 void onKeypress(int unicode)
 {
   /*
@@ -309,6 +311,16 @@ void runCPU(uint32_t now)
   static uint32_t countSinceLast = 0;
   static uint32_t microsAtStart = micros();
   static uint32_t microsForNext = microsAtStart + (countSinceLast * SPEEDCTL);
+
+  // Allow the BIOS to reset our timing
+  if (!cpuClockInitialized) {
+    nextResetMicros = 0;
+    countSinceLast = 0;
+    microsAtStart = micros();
+    microsForNext = microsAtStart + (countSinceLast * SPEEDCTL);
+
+    cpuClockInitialized = true;
+  }
   
   if (now >= microsForNext) {
     countSinceLast += g_cpu->Run(24); // The CPU runs in bursts of cycles. This '24' is the max burst we perform.
@@ -361,6 +373,8 @@ void loop()
       // Poll the keyboard before we start, so we can do selftest on startup
       g_keyboard->maintainKeyboard();
 
+      // Reset the CPU clock so it doesn't fast-forward
+      cpuClockInitialized = false;
       wasBios = false;
     }
   }