From bfb19f2938a37715d5b34d34e0b55c44907fcc19 Mon Sep 17 00:00:00 2001
From: David Reid <mackron@gmail.com>
Date: Mon, 26 Aug 2019 19:51:39 +1000
Subject: [PATCH] Experimental improvements for the ALSA backend.

---
 miniaudio.h       | 19 +++++--------------
 tests/ma_duplex.c | 12 +++++++++---
 2 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/miniaudio.h b/miniaudio.h
index ec6bc8ab..045a7ae5 100644
--- a/miniaudio.h
+++ b/miniaudio.h
@@ -13538,20 +13538,11 @@ ma_result ma_device_init_by_type__alsa(ma_context* pContext, const ma_device_con
         return ma_post_error(pDevice, MA_LOG_LEVEL_ERROR, "[ALSA] Failed to initialize software parameters. snd_pcm_sw_params_current() failed.", MA_FAILED_TO_CONFIGURE_BACKEND_DEVICE);
     }
 
-    if (deviceType == ma_device_type_capture) {
-        if (((ma_snd_pcm_sw_params_set_avail_min_proc)pContext->alsa.snd_pcm_sw_params_set_avail_min)(pPCM, pSWParams, 1) != 0) {
-            ma_free(pSWParams);
-            ((ma_snd_pcm_close_proc)pDevice->pContext->alsa.snd_pcm_close)(pPCM);
-            return ma_post_error(pDevice, MA_LOG_LEVEL_ERROR, "[ALSA] snd_pcm_sw_params_set_avail_min() failed.", MA_FORMAT_NOT_SUPPORTED);
-        }
-    } else {
-        if (((ma_snd_pcm_sw_params_set_avail_min_proc)pContext->alsa.snd_pcm_sw_params_set_avail_min)(pPCM, pSWParams, 1) != 0) {
-            ma_free(pSWParams);
-            ((ma_snd_pcm_close_proc)pDevice->pContext->alsa.snd_pcm_close)(pPCM);
-            return ma_post_error(pDevice, MA_LOG_LEVEL_ERROR, "[ALSA] snd_pcm_sw_params_set_avail_min() failed.", MA_FORMAT_NOT_SUPPORTED);
-        }
+    if (((ma_snd_pcm_sw_params_set_avail_min_proc)pContext->alsa.snd_pcm_sw_params_set_avail_min)(pPCM, pSWParams, ma_prev_power_of_2(internalBufferSizeInFrames/internalPeriods)) != 0) {
+        ma_free(pSWParams);
+        ((ma_snd_pcm_close_proc)pDevice->pContext->alsa.snd_pcm_close)(pPCM);
+        return ma_post_error(pDevice, MA_LOG_LEVEL_ERROR, "[ALSA] snd_pcm_sw_params_set_avail_min() failed.", MA_FORMAT_NOT_SUPPORTED);
     }
-    
 
     if (((ma_snd_pcm_sw_params_get_boundary_proc)pContext->alsa.snd_pcm_sw_params_get_boundary)(pSWParams, &bufferBoundary) < 0) {
         bufferBoundary = internalBufferSizeInFrames;
@@ -13564,7 +13555,7 @@ ma_result ma_device_init_by_type__alsa(ma_context* pContext, const ma_device_con
         Subtle detail here with the start threshold. When in playback-only mode (no full-duplex) we can set the start threshold to
         the size of a period. But for full-duplex we need to set it such that it is at least two periods.
         */
-        if (((ma_snd_pcm_sw_params_set_start_threshold_proc)pContext->alsa.snd_pcm_sw_params_set_start_threshold)(pPCM, pSWParams, internalBufferSizeInFrames) != 0) {
+        if (((ma_snd_pcm_sw_params_set_start_threshold_proc)pContext->alsa.snd_pcm_sw_params_set_start_threshold)(pPCM, pSWParams, (internalBufferSizeInFrames/internalPeriods)*2) != 0) {
             ma_free(pSWParams);
             ((ma_snd_pcm_close_proc)pDevice->pContext->alsa.snd_pcm_close)(pPCM);
             return ma_post_error(pDevice, MA_LOG_LEVEL_ERROR, "[ALSA] Failed to set start threshold for playback device. snd_pcm_sw_params_set_start_threshold() failed.", MA_FAILED_TO_CONFIGURE_BACKEND_DEVICE);
diff --git a/tests/ma_duplex.c b/tests/ma_duplex.c
index ae559e3e..deadb157 100644
--- a/tests/ma_duplex.c
+++ b/tests/ma_duplex.c
@@ -7,7 +7,7 @@
 #define DR_WAV_IMPLEMENTATION
 #include "../extras/dr_wav.h"
 
-#define OUTPUT_WAV 1
+#define OUTPUT_WAV 0
 
 #ifdef __EMSCRIPTEN__
 void main_loop__em()
@@ -63,11 +63,12 @@ int main(int argc, char** argv)
 #endif
     
 
-    ma_backend backend = ma_backend_winmm;
+    ma_backend backend = ma_backend_alsa;
 
     ma_context_config contextConfig = ma_context_config_init();
     contextConfig.logCallback = log_callback;
     contextConfig.alsa.useVerboseDeviceEnumeration = MA_TRUE;
+    contextConfig.threadPriority = ma_thread_priority_realtime;
 
     ma_context context;
     result = ma_context_init(&backend, 1, &contextConfig, &context);
@@ -107,13 +108,15 @@ int main(int argc, char** argv)
     deviceConfig.playback.format    = ma_format_s16;
     deviceConfig.playback.channels  = 2;
     deviceConfig.playback.shareMode = ma_share_mode_shared;
-    deviceConfig.sampleRate         = 50000;
+    deviceConfig.sampleRate         = 0;
     //deviceConfig.bufferSizeInMilliseconds = 60;
     deviceConfig.bufferSizeInFrames = 4096;
     //deviceConfig.periods            = 3;
     deviceConfig.dataCallback       = data_callback;
     deviceConfig.stopCallback       = stop_callback;
+#if defined(OUTPUT_WAV) && OUTPUT_WAV==1
     deviceConfig.pUserData          = &wav;
+#endif
 
     ma_device device;
     result = ma_device_init(&context, &deviceConfig, &device);
@@ -135,7 +138,10 @@ int main(int argc, char** argv)
 #endif
 
     ma_device_uninit(&device);
+
+#if defined(OUTPUT_WAV) && OUTPUT_WAV==1
     drwav_uninit(&wav);
+#endif
 
     (void)argc;
     (void)argv;