lr-virtualxt/tools/circle/kernel/emuloop.cpp

// Copyright (c) 2019-2026 Andreas T Jonsson <mail@andreasjonsson.se>
//
// This software is provided 'as-is', without any express or implied
// warranty. In no event will the authors be held liable for any damages
// arising from the use of this software.
//
// Permission is granted to anyone to use this software for any purpose,
// including commercial applications, and to alter it and redistribute it
// freely, subject to the following restrictions:
//
// 1. The origin of this software must not be misrepresented; you must not
//    claim that you wrote the original software. If you use this software
//    in a product, an acknowledgment in the product documentation would be
//    appreciated but is not required.
//
// 2. Altered source versions must be plainly marked as such, and must not be
//    misrepresented as being the original software.
//
// 3. This notice may not be removed or altered from any source
//    distribution.

#include "emuloop.h"
#include "kernel.h"
#include <circle/util.h>

#ifndef ARM_ALLOW_MULTI_CORE
	#error You need to enable multicore support!
#endif

extern struct retro_frame_time_callback frame_time;

extern "C" {
	void retro_run(void);
	void retro_set_video_refresh(retro_video_refresh_t cb);
	void retro_set_audio_sample_batch(retro_audio_sample_batch_t cb);
}

CSpinLock CEmuLoop::s_SpinLock(TASK_LEVEL);
CBcmFrameBuffer *CEmuLoop::s_pFrameBuffer(0);

unsigned screen_width = 0;
unsigned screen_height = 0;

#ifdef CRT_FILTER_EXTERNAL
#include <circle/atomic.h>
#include <circle/synchronize.h>
#include <frontend/crt.h>

// ── CRT filter offload + 4:3 letterbox scaling (Core 2 worker) ────────────
//
// When CRT_FILTER_EXTERNAL is defined, all framebuffer output is produced
// on Core 2. Core 1 only queues raw (or CRT-filtered intermediate) frames;
// Core 2 scales + letterboxes into the physical-resolution HW framebuffer.

#define CRT_MAX_WIDTH   720u
#define CRT_MAX_HEIGHT  700u
#define CRT_MAX_PIXELS  (CRT_MAX_WIDTH * CRT_MAX_HEIGHT)

static CBcmFrameBuffer *g_pHwFb = nullptr;
static unsigned g_hw_w = 0, g_hw_h = 0;
static unsigned g_hw_pitch = 0;
static unsigned g_target_x = 0, g_target_y = 0;
static unsigned g_target_w = 0, g_target_h = 0;
static int g_bars_drawn = 0;

static uint32_t core2_input[CRT_MAX_PIXELS];
static uint32_t core2_intermediate[CRT_MAX_PIXELS];
static unsigned core2_w = 0;
static unsigned core2_h = 0;

static volatile int core2_job_ready = 0;
static volatile int core2_apply_crt = 0;
static volatile int core2_reset_pending = 0;

static void ensure_hw_framebuffer(void) {
	if (g_pHwFb)
		return;

	g_pHwFb = new CBcmFrameBuffer(0, 0, 32);
	if (!g_pHwFb->Initialize()) {
		LOG(RETRO_LOG_WARN, "Could not auto-detect display size.");
		delete g_pHwFb;

		g_pHwFb = new CBcmFrameBuffer(1920, 1080, 32);
		if (!g_pHwFb->Initialize()) {
			LOG(RETRO_LOG_WARN, "Could not set 1920x1080 fallback.");
			delete g_pHwFb;

			g_pHwFb = new CBcmFrameBuffer(640, 480, 32);
			if (!g_pHwFb->Initialize()) {
				LOG(RETRO_LOG_ERROR, "Could not initialize any framebuffer!");
				delete g_pHwFb;
				g_pHwFb = nullptr;
				return;
			}
		}
	}

	g_hw_w = g_pHwFb->GetWidth();
	g_hw_h = g_pHwFb->GetHeight();
	g_hw_pitch = g_pHwFb->GetPitch();

	// Compute largest 4:3 rect that fits inside the physical display.
	g_target_h = g_hw_h;
	g_target_w = g_hw_h * 4 / 3;
	if (g_target_w > g_hw_w) {
		g_target_w = g_hw_w;
		g_target_h = g_hw_w * 3 / 4;
	}
	g_target_x = (g_hw_w - g_target_w) / 2;
	g_target_y = (g_hw_h - g_target_h) / 2;

	g_bars_drawn = 0;

	LOG(RETRO_LOG_INFO, "HW framebuffer: %ux%u, 4:3 target: %ux%u @ (%u,%u)",
	    g_hw_w, g_hw_h, g_target_w, g_target_h, g_target_x, g_target_y);
}

static void core2_blit_letterbox(const uint32_t *src, unsigned sw, unsigned sh) {
	if (!g_pHwFb)
		return;

	u8 *fb_base = (u8*)(u64)g_pHwFb->GetBuffer();

	if (!g_bars_drawn) {
		memset(fb_base, 0, g_hw_h * g_hw_pitch);
		g_bars_drawn = 1;
	}

	for (unsigned dy = 0; dy < g_target_h; dy++) {
		unsigned sy = (dy * sh) / g_target_h;
		const uint32_t *src_row = src + sy * sw;

#if RASPPI == 5
#define RGB555(red, green, blue) (((red) & 0x1F) << 11 | ((green) & 0x1F) << 6 | ((blue) & 0x1F))
		u16 *dst_row = (u16*)(fb_base + (g_target_y + dy) * g_hw_pitch) + g_target_x;
		for (unsigned dx = 0; dx < g_target_w; dx++) {
			unsigned sx = (dx * sw) / g_target_w;
			uint32_t p = src_row[sx];
			dst_row[dx] = RGB555((p >> 19) & 0x1F, (p >> 11) & 0x1F, (p >> 3) & 0x1F);
		}
#else
		uint32_t *dst_row = (uint32_t*)(fb_base + (g_target_y + dy) * g_hw_pitch) + g_target_x;
		for (unsigned dx = 0; dx < g_target_w; dx++) {
			unsigned sx = (dx * sw) / g_target_w;
			dst_row[dx] = src_row[sx];
		}
#endif
	}
}

// Trampolines — provided here when CRT_FILTER_EXTERNAL is defined.
extern "C" void crt_filter_apply(const uint32_t *src,
                                 unsigned width,
                                 unsigned height,
                                 uint32_t *dst) {
	(void)dst;
	if (width == 0 || height == 0)
		return;

	unsigned pixels = width * height;
	if (pixels > CRT_MAX_PIXELS)
		pixels = CRT_MAX_PIXELS;
	memcpy(core2_input, src, pixels * sizeof(uint32_t));

	core2_w = width;
	core2_h = height;

	DataSyncBarrier();
	AtomicSet(&core2_apply_crt, 1);
	AtomicSet(&core2_job_ready, 1);
	SendEvent();
}

extern "C" void crt_filter_reset(void) {
	AtomicSet(&core2_reset_pending, 1);
}

extern "C" unsigned crt_filter_output_height(unsigned height) {
	return crt_filter_output_height_impl(height);
}
#endif // CRT_FILTER_EXTERNAL

// ── Audio ring buffer ─────────────────────────────────────────────────────

#define AUDIO_RING_BUFFER_SIZE (SAMPLE_RATE * 2)  // 2 seconds of stereo samples

static int16_t audio_ring[AUDIO_RING_BUFFER_SIZE];
static volatile unsigned audio_ring_write = 0;
static volatile unsigned audio_ring_read = 0;

static unsigned audio_ring_count(void) {
	unsigned w = audio_ring_write;
	unsigned r = audio_ring_read;
	return (w >= r) ? (w - r) : (AUDIO_RING_BUFFER_SIZE - r + w);
}

static unsigned audio_ring_free(void) {
	return AUDIO_RING_BUFFER_SIZE - audio_ring_count() - 1;
}

static void audio_ring_write_samples(const int16_t *data, size_t frames) {
	unsigned free_space = audio_ring_free();
	unsigned to_write = (frames * 2 < free_space) ? (frames * 2) : free_space;

	for (unsigned i = 0; i < to_write; i++) {
		audio_ring[audio_ring_write] = data[i];
		audio_ring_write = (audio_ring_write + 1) % AUDIO_RING_BUFFER_SIZE;
	}
}

static unsigned audio_ring_read_samples(int16_t *data, unsigned samples) {
	unsigned avail = audio_ring_count();
	unsigned to_read = (samples < avail) ? samples : avail;

	for (unsigned i = 0; i < to_read; i++) {
		data[i] = audio_ring[audio_ring_read];
		audio_ring_read = (audio_ring_read + 1) % AUDIO_RING_BUFFER_SIZE;
	}
	return to_read;
}

// ── Libretro callbacks ────────────────────────────────────────────────────

extern "C" void video_refresh(const void *data, unsigned width, unsigned height, size_t pitch) {
	(void)pitch;

#ifdef CRT_FILTER_EXTERNAL
	(void)data;
	(void)width;
	(void)height;

	if (!g_pHwFb)
		ensure_hw_framebuffer();

	// If the trampoline already queued a CRT-filtered frame, nothing to do.
	// Otherwise queue the raw frame now.
	if (!AtomicGet(&core2_job_ready)) {
		unsigned pixels = width * height;
		if (pixels > CRT_MAX_PIXELS)
			pixels = CRT_MAX_PIXELS;
		memcpy(core2_input, data, pixels * sizeof(uint32_t));

		core2_w = width;
		core2_h = height;

		DataSyncBarrier();
		AtomicSet(&core2_apply_crt, 0);
		AtomicSet(&core2_job_ready, 1);
		SendEvent();
	}
#else
	if ((width != screen_width) || (height != screen_height) || !CEmuLoop::s_pFrameBuffer) {
		screen_width = width;
		screen_height = height;

		if (CEmuLoop::s_pFrameBuffer)
			delete CEmuLoop::s_pFrameBuffer;

		CEmuLoop::s_pFrameBuffer = new CBcmFrameBuffer(width, height, 32);

		if (!CEmuLoop::s_pFrameBuffer->Initialize()) {
			LOG(RETRO_LOG_WARN, "Could not set correct resolution. Fallback to virtual resolution.");

			delete CEmuLoop::s_pFrameBuffer;
			CEmuLoop::s_pFrameBuffer = new CBcmFrameBuffer(640, 480, 32, width, height);

			if (!CEmuLoop::s_pFrameBuffer->Initialize()) {
				LOG(RETRO_LOG_ERROR, "Could not initialize framebuffer!");
				delete CEmuLoop::s_pFrameBuffer;
				return;
			}
		}
	}

	const u8 *rgba = (const u8*)data;

	u8 *buffer = (u8*)(u64)CEmuLoop::s_pFrameBuffer->GetBuffer();

	for (unsigned i = 0; i < height; i++) {
		#if RASPPI == 5
			#define RGB555(red, green, blue) (((red) & 0x1F) << 11 | ((green) & 0x1F) << 6 | ((blue) & 0x1F))
			for (unsigned j = 0; j < width; j++) {
				((u16*)buffer)[j] = RGB555(rgba[2] >> 3, rgba[1] >> 3, rgba[0] >> 3);
				rgba += 4;
			}
		#else
			memcpy(buffer, rgba, 4 * width);
			rgba += 4 * width;
		#endif
		buffer += CEmuLoop::s_pFrameBuffer->GetPitch();
	}
#endif
}

extern "C" size_t audio_batch(const int16_t *data, size_t frames) {
	audio_ring_write_samples(data, frames);
	return frames;
}

// ── CEmuLoop implementation ───────────────────────────────────────────────

CEmuLoop::CEmuLoop(
	CMemorySystem *mem, CKernelOptions *opt, CBcmFrameBuffer *fb,
	CSoundBaseDevice *snd, unsigned al)
:
	CMultiCoreSupport(mem),
	m_pOptions(opt),
	m_pSound(snd),
	m_AudioLatency(al)
{
	assert(CLOCKHZ == 1000000);
	s_pFrameBuffer = fb;

	retro_set_video_refresh(&video_refresh);
	retro_set_audio_sample_batch(&audio_batch);
}

CEmuLoop::~CEmuLoop(void) {
	SendIPI(1, IPI_HALT_CORE); // EmuThread
	SendIPI(2, IPI_HALT_CORE); // RenderThread
	SendIPI(3, IPI_HALT_CORE); // AudioThread
}

void CEmuLoop::Lock(void) {
	s_SpinLock.Acquire();
}

void CEmuLoop::Unlock(void) {
	s_SpinLock.Release();
}

void CEmuLoop::Run(unsigned nCore) {
	switch (nCore) {
		case 1: EmuThread(); break;
		case 2: RenderThread(); break;
		case 3: AudioThread(); break;
	}
}

void CEmuLoop::EmuThread(void) {
	LOGI("Emulation thread started!");

	for (u64 ticks = CTimer::GetClockTicks64(); CKernel::Get()->m_ShutdownMode == ShutdownNone;) {
		u64 now = CTimer::GetClockTicks64();
		u64 dt = now - ticks;

		if (dt >= (CLOCKHZ / 60)) {
			Lock();
			if (frame_time.callback)
				frame_time.callback(dt);
			retro_run();
			Unlock();

			ticks = now;
		}
	}

	LOGI("Emulation thread ended!");
}

void CEmuLoop::RenderThread(void) {
	LOGI("Render thread started!");

#ifdef CRT_FILTER_EXTERNAL
	for (; CKernel::Get()->m_ShutdownMode == ShutdownNone;) {
		if (!AtomicGet(&core2_job_ready)) {
			WaitForEvent();
			continue;
		}

		if (AtomicGet(&core2_reset_pending)) {
			crt_filter_reset_impl();
			AtomicSet(&core2_reset_pending, 0);
		}

		const uint32_t *src = core2_input;
		unsigned sw = core2_w;
		unsigned sh = core2_h;

		if (AtomicGet(&core2_apply_crt)) {
			crt_filter_apply_impl(core2_input, sw, sh, core2_intermediate);
			src = core2_intermediate;
			sh = crt_filter_output_height_impl(sh);
			AtomicSet(&core2_apply_crt, 0);
		}

		core2_blit_letterbox(src, sw, sh);

		DataSyncBarrier();
		AtomicSet(&core2_job_ready, 0);
	}
#else
	for (u64 ticks = CTimer::GetClockTicks64(); CKernel::Get()->m_ShutdownMode == ShutdownNone;) {
		u64 now = CTimer::GetClockTicks64();
		if ((now - ticks) >= (CLOCKHZ / 60)) {
			ticks = now;
			// Rendering is done synchronously in video_refresh callback.
			// This thread can be used for future post-processing or VSync.
		}
	}
#endif

	LOGI("Render thread ended!");
}

void CEmuLoop::AudioThread(void) {
	if (!m_pSound)
		return;

	LOGI("Audio thread started!");

	const unsigned chunk_samples = CHUNK_SIZE * 2; // stereo
	DMA_BUFFER(int16_t, audio_chunk, chunk_samples);

	u64 audio_ticks = CTimer::GetClockTicks64();

	for (u64 ticks = audio_ticks; CKernel::Get()->m_ShutdownMode == ShutdownNone; ticks = CTimer::GetClockTicks64()) {
		if ((ticks - audio_ticks) >= (CLOCKHZ / 1000)) {  // 1ms granularity
			audio_ticks = ticks;

			if (m_pSound && m_pSound->IsActive()) {
				unsigned samples_needed = m_pSound->GetQueueSizeFrames() - m_pSound->GetQueueFramesAvail();
				samples_needed *= 2; // stereo

				while (samples_needed > 0) {
					unsigned to_read = (samples_needed < chunk_samples) ? samples_needed : chunk_samples;
					unsigned read = audio_ring_read_samples(audio_chunk, to_read);
					if (read == 0)
						break;

					m_pSound->Write((u8*)audio_chunk, read * sizeof(int16_t));
					samples_needed -= read;
				}
			}
		}
	}

	LOGI("Audio thread ended!");
}