[APU] Add ALSA apu on Linux

src/xenia/apu/alsa/alsa_audio_driver.h

@@ -0,0 +1,99 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2025. All rights reserved.                                       *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#ifndef XENIA_APU_ALSA_ALSA_AUDIO_DRIVER_H_
+#define XENIA_APU_ALSA_ALSA_AUDIO_DRIVER_H_
+
+#include <alsa/asoundlib.h>
+#include <atomic>
+#include <memory>
+#include <thread>
+
+#include "xenia/apu/audio_driver.h"
+#include "xenia/base/threading.h"
+
+namespace xe {
+namespace apu {
+namespace alsa {
+
+class ALSAAudioDriver : public AudioDriver {
+ public:
+  ALSAAudioDriver(xe::threading::Semaphore* semaphore,
+                  uint32_t frequency = kFrameFrequencyDefault,
+                  uint32_t channels = kFrameChannelsDefault,
+                  bool need_format_conversion = true);
+  ~ALSAAudioDriver() override;
+
+  bool Initialize() override;
+  void SubmitFrame(float* frame) override;
+  void Pause() override;
+  void Resume() override;
+  void SetVolume(float volume) override { volume_.store(volume); }
+  void Shutdown() override;
+
+ private:
+  void WorkerThread();
+  bool SetupAlsaDevice();
+  bool RecoverFromUnderrun(int err);
+  void ConvertChannels(const float* input, float* output,
+                       size_t channel_samples);
+  size_t ResampleFrame(const float* input, float* output,
+                       size_t input_frame_count, size_t output_capacity_frames,
+                       float frequency_ratio, uint32_t channels);
+  void ApplyVolume(float* buffer, size_t sample_count, float volume);
+
+  xe::threading::Semaphore* semaphore_ = nullptr;
+
+  // ALSA handles
+  snd_pcm_t* pcm_handle_ = nullptr;
+  snd_pcm_hw_params_t* hw_params_ = nullptr;
+  snd_pcm_sw_params_t* sw_params_ = nullptr;
+
+  // Device configuration
+  uint32_t frame_frequency_;
+  uint32_t frame_channels_;
+  uint32_t channel_samples_;
+  uint32_t frame_size_;
+  bool need_format_conversion_;
+
+  // Output configuration (may differ from input)
+  uint32_t output_channels_ = 0;
+  snd_pcm_uframes_t period_size_ = 0;
+  snd_pcm_uframes_t buffer_size_ = 0;
+
+  // Threading
+  std::unique_ptr<std::thread> worker_thread_;
+  std::atomic<bool> running_{false};
+  std::atomic<bool> paused_{false};
+  std::atomic<float> volume_{1.0f};
+
+  // Ring buffer for frames (larger size to reduce underruns)
+  static constexpr size_t kRingBufferSize = 32;
+  float* ring_buffer_[kRingBufferSize] = {};
+  std::atomic<size_t> read_index_{0};
+  std::atomic<size_t> write_index_{0};
+
+  // ALSA period and buffer configuration
+  static constexpr snd_pcm_uframes_t kPeriodSize51 = 512;
+  static constexpr snd_pcm_uframes_t kPeriodSizeStereo = 1024;
+  static constexpr size_t kBufferPeriods = 4;
+
+  // Conversion buffer
+  std::unique_ptr<float[]> conversion_buffer_;
+
+  // Time scaling / resampling state
+  std::unique_ptr<float[]> resample_buffer_;
+  double resample_frac_position_ = 0.0;
+};
+
+}  // namespace alsa
+}  // namespace apu
+}  // namespace xe
+
+#endif  // XENIA_APU_ALSA_ALSA_AUDIO_DRIVER_H_