From 90a4f28c2799e3ae5e873f1f34b1e4adb59f77cb Mon Sep 17 00:00:00 2001
From: Solomon Peachy <pizza@shaftnet.org>
Date: Fri, 4 Sep 2020 15:55:11 -0400
Subject: jz47xx:  Audio path tweaks:

 * Increase audio buffer size to better handle IRQ latency (256->2048)
 * Ensure DMA engine is idle prior to starting transfers
 * Set AIC to repeat last sample in case of underflows

Change-Id: I9c45c20481ee072e5882b7586fb7d50bd8ef2f35
---
 firmware/export/pcm_mixer.h                        | 4 ++++
 firmware/target/mips/ingenic_jz47xx/codec-jz4740.c | 1 +
 firmware/target/mips/ingenic_jz47xx/codec-jz4760.c | 1 +
 firmware/target/mips/ingenic_jz47xx/pcm-jz4740.c   | 2 ++
 firmware/target/mips/ingenic_jz47xx/pcm-jz4760.c   | 2 ++
 5 files changed, 10 insertions(+)

diff --git a/firmware/export/pcm_mixer.h b/firmware/export/pcm_mixer.h
index b418a5d347..3d255a7345 100644
--- a/firmware/export/pcm_mixer.h
+++ b/firmware/export/pcm_mixer.h
@@ -30,6 +30,10 @@
 #if CONFIG_CPU == PP5002
 /* There's far less time to do mixing because HW FIFOs are short */
 #define MIX_FRAME_SAMPLES 64
+#elif (CONFIG_CPU == JZ4760B) || (CONFIG_CPU == JZ4732)
+/* These MIPS32r1 targets have a very high interrupt latency, which
+   unfortunately causes a lot of audio underruns under even moderate load */
+#define MIX_FRAME_SAMPLES 2048
 #elif (CONFIG_PLATFORM & PLATFORM_MAEMO5) || defined(DX50) || defined(DX90)
 /* Maemo 5 needs 2048 samples for decent performance.
    Otherwise the locking overhead inside gstreamer costs too much */
diff --git a/firmware/target/mips/ingenic_jz47xx/codec-jz4740.c b/firmware/target/mips/ingenic_jz47xx/codec-jz4740.c
index 702f3bb50e..a41f047026 100644
--- a/firmware/target/mips/ingenic_jz47xx/codec-jz4740.c
+++ b/firmware/target/mips/ingenic_jz47xx/codec-jz4740.c
@@ -267,6 +267,7 @@ void audiohw_postinit(void)
 
 void audiohw_init(void)
 {
+    __aic_play_lastsample(); /* on FIFO underflow */
     i2s_codec_init();
 }
 
diff --git a/firmware/target/mips/ingenic_jz47xx/codec-jz4760.c b/firmware/target/mips/ingenic_jz47xx/codec-jz4760.c
index bc4286fd6a..60bfecb08c 100644
--- a/firmware/target/mips/ingenic_jz47xx/codec-jz4760.c
+++ b/firmware/target/mips/ingenic_jz47xx/codec-jz4760.c
@@ -115,6 +115,7 @@ void audiohw_init(void)
     __cpm_start_aic();
 
     /* Init AIC */
+    __aic_play_lastsample(); /* on FIFO underflow.  Versus 0.. */
     __i2s_enable_sclk();
     __i2s_external_codec();
     __i2s_select_msbjustified();
diff --git a/firmware/target/mips/ingenic_jz47xx/pcm-jz4740.c b/firmware/target/mips/ingenic_jz47xx/pcm-jz4740.c
index 00a2b22591..ef2597ae69 100644
--- a/firmware/target/mips/ingenic_jz47xx/pcm-jz4740.c
+++ b/firmware/target/mips/ingenic_jz47xx/pcm-jz4740.c
@@ -137,6 +137,8 @@ void DMA_CALLBACK(DMA_AIC_TX_CHANNEL)(void)
 
 void pcm_play_dma_start(const void *addr, size_t size)
 {
+    pcm_play_dma_stop();
+
     dma_enable();
 
     set_dma(addr, size);
diff --git a/firmware/target/mips/ingenic_jz47xx/pcm-jz4760.c b/firmware/target/mips/ingenic_jz47xx/pcm-jz4760.c
index 59b086e4f8..098c28ecf5 100644
--- a/firmware/target/mips/ingenic_jz47xx/pcm-jz4760.c
+++ b/firmware/target/mips/ingenic_jz47xx/pcm-jz4760.c
@@ -128,6 +128,8 @@ void DMA_CALLBACK(DMA_AIC_TX_CHANNEL)(void)
 
 void pcm_play_dma_start(const void *addr, size_t size)
 {
+    pcm_play_dma_stop();
+
     __dmac_channel_enable_clk(DMA_AIC_TX_CHANNEL);
 
     set_dma(addr, size);
-- 
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