From 0da7ead0a84f6ded885a8b47654543dee70e0957 Mon Sep 17 00:00:00 2001
From: jacqueline <me@jacqueline.id.au>
Date: Fri, 24 May 2024 15:12:41 +1000
Subject: [PATCH] Simply some I2SDac management to avoid null pointer accesses

Fixes #72; we were destroying the I2SDac instance, but weren't actually
recording that the output was now in the 'off' state.
---
 src/tangara/audio/i2s_audio_output.cpp | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/tangara/audio/i2s_audio_output.cpp b/src/tangara/audio/i2s_audio_output.cpp
index 684bfa92..d7be9a4b 100644
--- a/src/tangara/audio/i2s_audio_output.cpp
+++ b/src/tangara/audio/i2s_audio_output.cpp
@@ -62,14 +62,21 @@ auto I2SAudioOutput::changeMode(Modes mode) -> void {
   if (mode == current_mode_) {
     return;
   }
+  bool was_off = current_mode_ == Modes::kOff;
+  current_mode_ = mode;
+
   if (mode == Modes::kOff) {
+    // Turning off this output. Ensure we clean up the I2SDac instance to
+    // reclaim its valuable DMA buffers.
     if (dac_) {
       dac_->Stop();
       dac_.reset();
     }
     return;
   }
-  if (current_mode_ == Modes::kOff) {
+
+  if (was_off) {
+    // Ensure an I2SDac instance actually exists.
     if (!dac_) {
       auto instance = drivers::I2SDac::create(expander_);
       if (!instance) {
@@ -77,10 +84,12 @@ auto I2SAudioOutput::changeMode(Modes mode) -> void {
       }
       dac_.reset(*instance);
     }
+    // Set up the new instance properly.
     SetVolume(GetVolume());
     dac_->SetSource(stream());
     dac_->Start();
   }
+
   current_mode_ = mode;
   dac_->SetPaused(mode == Modes::kOnPaused);
 }