From 265049c5192cf0ce862c7db7b4745636afb6c17b Mon Sep 17 00:00:00 2001
From: jacqueline <me@jacqueline.id.au>
Date: Wed, 8 May 2024 16:03:03 +1000
Subject: Count samples going in and out of the drain buffer

This is a more accurate way of knowing which track is playing when, and
also simplifies a lot of fragile logic in audio_fsm
---
 src/drivers/i2s_dac.cpp | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

(limited to 'src/drivers/i2s_dac.cpp')

diff --git a/src/drivers/i2s_dac.cpp b/src/drivers/i2s_dac.cpp
index a271fce0..e5efe198 100644
--- a/src/drivers/i2s_dac.cpp
+++ b/src/drivers/i2s_dac.cpp
@@ -5,6 +5,7 @@
  */
 
 #include "drivers/i2s_dac.hpp"
+#include <stdint.h>
 
 #include <cmath>
 #include <cstdint>
@@ -140,11 +141,10 @@ auto I2SDac::SetPaused(bool paused) -> void {
   }
 }
 
-static volatile bool sSwapWords = false;
+DRAM_ATTR static volatile bool sSwapWords = false;
 
-auto I2SDac::Reconfigure(Channels ch,
-                         BitsPerSample bps,
-                         SampleRate rate) -> void {
+auto I2SDac::Reconfigure(Channels ch, BitsPerSample bps, SampleRate rate)
+    -> void {
   std::lock_guard<std::mutex> lock(configure_mutex_);
 
   if (i2s_active_) {
@@ -217,6 +217,8 @@ auto I2SDac::WriteData(const std::span<const std::byte>& data) -> void {
   }
 }
 
+DRAM_ATTR static volatile uint32_t sSamplesRead = 0;
+
 extern "C" IRAM_ATTR auto callback(i2s_chan_handle_t handle,
                                    i2s_event_data_t* event,
                                    void* user_ctx) -> bool {
@@ -235,6 +237,14 @@ extern "C" IRAM_ATTR auto callback(i2s_chan_handle_t handle,
   size_t bytes_written =
       xStreamBufferReceiveFromISR(src, buf, event->size, &ret);
 
+  // Assume 16 bit samples.
+  size_t samples = bytes_written / 2;
+  if (UINT32_MAX - sSamplesRead < samples) {
+    sSamplesRead = samples - (UINT32_MAX - sSamplesRead);
+  } else {
+    sSamplesRead = sSamplesRead + samples;
+  }
+
   // The ESP32's I2S peripheral has a different endianness to its processors.
   // ESP-IDF handles this difference for stereo channels, but not for mono
   // channels. We therefore sometimes need to swap each pair of words as they're
@@ -276,6 +286,10 @@ auto I2SDac::SetSource(StreamBufferHandle_t buffer) -> void {
   }
 }
 
+auto I2SDac::SamplesUsed() -> uint32_t {
+  return sSamplesRead;
+}
+
 auto I2SDac::set_channel(bool enabled) -> void {
   if (i2s_active_ == enabled) {
     return;
-- 
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