From 81ba5be37da79acfeddb7537ccede37957251eb1 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Tue, 31 Mar 2026 23:43:21 -0400
Subject: [PATCH 1/2] Switch to DAC, support music and game music output.

---
 Machines/Thomson/MO5/MO5.cpp | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/Machines/Thomson/MO5/MO5.cpp b/Machines/Thomson/MO5/MO5.cpp
index d2722e0b7..6283b9375 100644
--- a/Machines/Thomson/MO5/MO5.cpp
+++ b/Machines/Thomson/MO5/MO5.cpp
@@ -56,8 +56,8 @@ struct ConcreteMachine:
 		sound_and_game_pia_(sound_and_game_pia_port_handler_),
 		video_(video_page(true), video_page(false)),
 		tape_player_(ClockRate),
-		audio_toggle_(audio_queue_),
-		speaker_(audio_toggle_)
+		audio_(audio_queue_, 63),
+		speaker_(audio_)
 	{
 		set_clock_rate(ClockRate);
 		speaker_.set_input_rate(ClockRate);
@@ -263,8 +263,7 @@ private:
 				//		b1–3 = keyboard column;
 				//		b4–6: keyboard line;
 				key_ = (value >> 1) & 0b111'111;
-				machine_.update_audio();
-				machine_.audio_toggle_.set_output(value & 1);
+				machine_.set_audio(value & 1, std::nullopt);
 			}
 		}
 
@@ -313,11 +312,13 @@ private:
 		void observe(const bool) {}
 
 		template <Motorola::MC6821::Port port>
-		void output(const uint8_t) {
-			// TODO: sound.
+		void output(const uint8_t value) {
 			// Port B:
 			//
 			//	b0–b5: DAC output
+			if constexpr (port == Motorola::MC6821::Port::B) {
+				machine_.set_audio(std::nullopt, value & 63);
+			}
 		}
 
 		template <Motorola::MC6821::IRQ irq>
@@ -445,8 +446,8 @@ private:
 	// MARK: - AudioProducer.
 
 	Concurrency::AsyncTaskQueue<false> audio_queue_;
-	Audio::Toggle audio_toggle_;
-	Outputs::Speaker::PullLowpass<Audio::Toggle> speaker_;
+	Audio::DAC audio_;
+	Outputs::Speaker::PullLowpass<Audio::DAC> speaker_;
 
 	Cycles time_since_audio_update_;
 	void update_audio() {
@@ -458,6 +459,15 @@ private:
 		return &speaker_;
 	}
 
+	bool audio_enabled_ = false;
+	uint8_t audio_level_ = 63;
+	void set_audio(const std::optional<bool> enabled, const std::optional<uint8_t> level) {
+		update_audio();
+		audio_enabled_ = enabled.value_or(audio_enabled_);
+		audio_level_ = level.value_or(audio_level_);
+		audio_.set_output(audio_enabled_ ? audio_level_ : 0);
+	}
+
 	// MARK: - ScanProducer.
 
 	void set_scan_target(Outputs::Display::ScanTarget *const target) final {

From c78701efac604a3a4ef930cef3571949c4b5e22f Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Wed, 1 Apr 2026 08:36:39 -0400
Subject: [PATCH 2/2] Pull out magic constant.

---
 Machines/Thomson/MO5/MO5.cpp | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/Machines/Thomson/MO5/MO5.cpp b/Machines/Thomson/MO5/MO5.cpp
index 6283b9375..fb3f538c0 100644
--- a/Machines/Thomson/MO5/MO5.cpp
+++ b/Machines/Thomson/MO5/MO5.cpp
@@ -34,6 +34,7 @@ namespace {
 using Log = Log::Logger<Log::Source::MO5>;
 
 static constexpr int ClockRate = 1'000'000;
+static constexpr uint8_t MusicExpansionMask = 63;
 
 struct ConcreteMachine:
 	public Activity::Source,
@@ -56,7 +57,7 @@ struct ConcreteMachine:
 		sound_and_game_pia_(sound_and_game_pia_port_handler_),
 		video_(video_page(true), video_page(false)),
 		tape_player_(ClockRate),
-		audio_(audio_queue_, 63),
+		audio_(audio_queue_, MusicExpansionMask),
 		speaker_(audio_)
 	{
 		set_clock_rate(ClockRate);
@@ -317,7 +318,7 @@ private:
 			//
 			//	b0–b5: DAC output
 			if constexpr (port == Motorola::MC6821::Port::B) {
-				machine_.set_audio(std::nullopt, value & 63);
+				machine_.set_audio(std::nullopt, value & MusicExpansionMask);
 			}
 		}
 
@@ -460,7 +461,7 @@ private:
 	}
 
 	bool audio_enabled_ = false;
-	uint8_t audio_level_ = 63;
+	uint8_t audio_level_ = MusicExpansionMask;
 	void set_audio(const std::optional<bool> enabled, const std::optional<uint8_t> level) {
 		update_audio();
 		audio_enabled_ = enabled.value_or(audio_enabled_);