From 37ca0e4f81f3ec58525048da2fe63da5fc8d27ab Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 30 Oct 2025 22:23:01 -0400
Subject: [PATCH] Introduce one-directional FIFO.

---
 Machines/Acorn/Tube/FIFO.hpp                  | 37 +++++++++++++++++++
 .../Clock Signal.xcodeproj/project.pbxproj    | 10 +++++
 2 files changed, 47 insertions(+)
 create mode 100644 Machines/Acorn/Tube/FIFO.hpp

diff --git a/Machines/Acorn/Tube/FIFO.hpp b/Machines/Acorn/Tube/FIFO.hpp
new file mode 100644
index 000000000..49484fa9d
--- /dev/null
+++ b/Machines/Acorn/Tube/FIFO.hpp
@@ -0,0 +1,37 @@
+//
+//  Header.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 30/10/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+namespace Acorn::Tube {
+
+template <size_t length>
+struct FIFO {
+	uint8_t status() const {
+		return
+			((read != write) ? 0x80 : 0x00) |
+			((write - read < length) ? 0x40 : 0x00);
+	}
+
+	void write(const uint8_t value) {
+		if(write - read == length) return;
+		buffer[write++] = value;
+	}
+
+	void read() {
+		const uint8_t result = buffer[read];
+		if(write != read) ++read;
+	}
+
+private:
+	std::array<uint8_t, length> buffer;
+	uint32_t read = 0;
+	uint32_t write = 0;
+};
+
+}
diff --git a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj
index e63f14720..6c05480af 100644
--- a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
+++ b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
@@ -1612,6 +1612,7 @@
 		4B49F0A823346F7A0045E6A6 /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.xib; name = Base; path = "Clock Signal/Base.lproj/MacintoshOptions.xib"; sourceTree = SOURCE_ROOT; };
 		4B4A75BC2EB2C55100EA398F /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.xib; name = Base; path = Base.lproj/CompositeDynamicCropOptions.xib; sourceTree = "<group>"; };
 		4B4A75BF2EB399D700EA398F /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.xib; name = Base; path = Base.lproj/DynamicCropOptions.xib; sourceTree = "<group>"; };
+		4B4A75C22EB43F1C00EA398F /* FIFO.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = FIFO.hpp; sourceTree = "<group>"; };
 		4B4A762E1DB1A3FA007AAE2E /* AY38910.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = AY38910.cpp; sourceTree = "<group>"; };
 		4B4A762F1DB1A3FA007AAE2E /* AY38910.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = AY38910.hpp; sourceTree = "<group>"; };
 		4B4B1A3A200198C900A0F866 /* KonamiSCC.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = KonamiSCC.cpp; sourceTree = "<group>"; };
@@ -3354,6 +3355,14 @@
 			path = uPD7002;
 			sourceTree = "<group>";
 		};
+		4B4A75C32EB43F1C00EA398F /* Tube */ = {
+			isa = PBXGroup;
+			children = (
+				4B4A75C22EB43F1C00EA398F /* FIFO.hpp */,
+			);
+			path = Tube;
+			sourceTree = "<group>";
+		};
 		4B4A762D1DB1A35C007AAE2E /* AY38910 */ = {
 			isa = PBXGroup;
 			children = (
@@ -4673,6 +4682,7 @@
 		4BB505682B962DDF0031C43C /* Acorn */ = {
 			isa = PBXGroup;
 			children = (
+				4B4A75C32EB43F1C00EA398F /* Tube */,
 				4BB505692B962DDF0031C43C /* Archimedes */,
 				4B710C8C2E77A3B20056BDF4 /* BBCMicro */,
 				4BB5056A2B962DDF0031C43C /* Electron */,