[nostalgia] Break part of core out into Turbine and TeaGBA libraries

src/turbine/gba/turbine.cpp

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2016 - 2023 Gary Talent (gary@drinkingtea.net). All rights reserved.
+ */
+
+#include <teagba/addresses.hpp>
+#include <teagba/irq.hpp>
+
+#include <keel/keel.hpp>
+#include <turbine/gfx.hpp>
+
+#include "context.hpp"
+#include "turbine.hpp"
+
+extern "C" void isr();
+
+namespace turbine {
+
+// Timer Consts
+constexpr int NanoSecond = 1000000000;
+constexpr int MilliSecond = 1000;
+constexpr int TicksMs59ns = 65535 - (NanoSecond / MilliSecond) / 59.59;
+
+extern volatile gba_timer_t g_timerMs;
+
+static void initIrq() noexcept {
+	REG_ISR = isr;
+	REG_IME = 1; // enable interrupts
+}
+
+static void initTimer() noexcept {
+	// make timer0 a ~1 millisecond timer
+	REG_TIMER0 = TicksMs59ns;
+	REG_TIMER0CTL = 0b11000000;
+	// enable interrupt for timer0
+	REG_IE = REG_IE | teagba::Int_timer0;
+}
+
+static ox::Result<std::size_t> findPreloadSection() noexcept {
+	// put the header in the wrong order to prevent mistaking this code for the
+	// media section
+	constexpr auto headerP2 = "DER_____________";
+	constexpr auto headerP1 = "KEEL_PRELOAD_HEA";
+	constexpr auto headerP1Len = ox_strlen(headerP2);
+	constexpr auto headerP2Len = ox_strlen(headerP1);
+	constexpr auto headerLen = headerP1Len + headerP2Len;
+	for (auto current = MEM_ROM; current < reinterpret_cast<char*>(0x0a000000); current += headerLen) {
+		if (ox_memcmp(current, headerP1, headerP1Len) == 0 &&
+		    ox_memcmp(current + headerP1Len, headerP2, headerP2Len) == 0) {
+			return reinterpret_cast<std::size_t>(current + headerLen);
+		}
+	}
+	return OxError(1);
+}
+
+ox::Result<ox::UniquePtr<turbine::Context>> init(ox::UPtr<ox::FileSystem> fs, ox::CRStringView appName) noexcept {
+	oxRequireM(ctx, keel::init<gba::Context>(std::move(fs), appName));
+	oxReturnError(findPreloadSection().moveTo(&ctx->preloadSectionOffset));
+	oxReturnError(initGfx(*ctx));
+	initTimer();
+	initIrq();
+	return ox::UPtr<turbine::Context>(std::move(ctx));
+}
+
+void shutdown(Context&) noexcept {
+}
+
+uint64_t ticksMs(Context&) noexcept {
+	return g_timerMs;
+}
+
+bool buttonDown(Context&, Key k) noexcept {
+	return k <= Key::GamePad_L && !(REG_GAMEPAD & (1 << static_cast<int>(k)));
+}
+
+void requestShutdown(Context &ctx) noexcept {
+	const auto gbaCtx = static_cast<gba::Context*>(&ctx);
+	gbaCtx->running = false;
+}
+
+}