From ae2936b9c3f8245e8dc7ab233bbe1af79cbdafe9 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Mon, 10 Nov 2025 22:35:13 -0500
Subject: [PATCH] Correct clock rate, triangle wave.

---
 Components/SID/SID.cpp               | 5 ++++-
 Components/SID/SID.hpp               | 5 +++--
 Machines/Acorn/BBCMicro/BBCMicro.cpp | 6 +++---
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/Components/SID/SID.cpp b/Components/SID/SID.cpp
index 7ce118e36..cbcf36f9c 100644
--- a/Components/SID/SID.cpp
+++ b/Components/SID/SID.cpp
@@ -35,7 +35,10 @@ void SID::write(const Numeric::SizedInt<5> address, const uint8_t value) {
 				oscillator().pulse_width = (oscillator().pitch & 0xf0'00'00'00) | uint32_t(value << 20);
 			break;
 			case 0x03:	case 0x0a:	case 0x11:
-				oscillator().pulse_width = (oscillator().pitch & 0x0f'f0'00'00) | uint32_t(value << 28);
+				// The top bit of the phase counter is inverted; since it'll be compared directly with the
+				// pulse width, invert that bit too.
+				oscillator().pulse_width =
+					((oscillator().pitch & 0x0f'f0'00'00) | uint32_t(value << 28)) ^ 0x8000'0000;
 			break;
 			case 0x04:	case 0x0b:	case 0x12:
 				voice().control = value;
diff --git a/Components/SID/SID.hpp b/Components/SID/SID.hpp
index 0af6307f5..b31046d7d 100644
--- a/Components/SID/SID.hpp
+++ b/Components/SID/SID.hpp
@@ -116,8 +116,9 @@ private:
 
 		uint16_t triangle_output(const Voice &prior) const {
 			const uint16_t sawtooth = oscillator.sawtooth();
-			const uint16_t xor_mask =
-				((sawtooth ^ (ring_mod() && prior.sawtooth())) & 0x800) ? 0xfff : 0x000;
+			const uint16_t xor_mask1 = sawtooth;
+			const uint16_t xor_mask2 = ring_mod() ? prior.sawtooth() : 0;
+			const uint16_t xor_mask = (xor_mask1 ^ xor_mask2) ? 0xfff : 0x000;
 			return ((sawtooth << 1) ^ xor_mask) & 0xfff;
 		}
 
diff --git a/Machines/Acorn/BBCMicro/BBCMicro.cpp b/Machines/Acorn/BBCMicro/BBCMicro.cpp
index 7e043a2e1..ccde89530 100644
--- a/Machines/Acorn/BBCMicro/BBCMicro.cpp
+++ b/Machines/Acorn/BBCMicro/BBCMicro.cpp
@@ -128,13 +128,13 @@ private:
 
 public:
 	Audio() :
-		sn76489_(TI::SN76489::Personality::SN76489, audio_queue_, 2),
+		sn76489_(TI::SN76489::Personality::SN76489, audio_queue_, 4),
 		sid_(audio_queue_),
 		compound_(sn76489_, sid_),
 		speaker_(speaker_source())
 	{
-		// Combined with the additional divider specified above, implies this chip is clocked at 4Mhz.
-		speaker_.set_input_rate(2'000'000.0f);
+		// Combined with the additional divider specified above, implies the SN76489 is clocked at 4Mhz.
+		speaker_.set_input_rate(1'000'000.0f);
 	}
 
 	~Audio() {