[nostalgia/core] Add ticksMs() function

src/nostalgia/core/gba/core.cpp

@@ -1,20 +1,45 @@
 /*
- * Copyright 2016 - 2019 gtalent2@gmail.com
+ * Copyright 2016 - 2020 gary@drinkingtea.net
  *
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
+#include <nostalgia/core/config.hpp>
 #include <nostalgia/core/core.hpp>
 
+#include "addresses.hpp"
 #include "irq.hpp"
 
+extern "C" void isr();
+
 namespace nostalgia::core {
 
+// Timer Consts
+constexpr auto NanoSecond = 1000000000;
+constexpr auto MilliSecond = 1000;
+constexpr int TicksMs59ns = (NanoSecond / MilliSecond) / 59.59;
+
+extern volatile ox::Uint<config::GbaTimerBits> g_timerMs;
+
+static void initIrq() {
+	REG_ISR = isr;
+	REG_IME = 1; // enable interrupts
+}
+
+static void initTimer() {
+	// make timer0 a ~1 millisecond timer
+	REG_TIMER0 = TicksMs59ns;
+	REG_TIMER0CTL = 0b11000011;
+	// enable interrupt for timer0
+	REG_IE |= Int_timer0;
+}
+
 ox::Error init(Context *ctx) {
 	oxReturnError(initGfx(ctx));
-	oxReturnError(initIrq(ctx));
+	initTimer();
+	initIrq();
 	return OxError(0);
 }
 
@@ -24,4 +49,8 @@ ox::Error run(Context*) {
 	return OxError(0);
 }
 
+uint64_t ticksMs() {
+	return g_timerMs;
+}
+
 }