From 8a765031e1a0e66419f0fe4e2dc361baf20e8568 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sun, 12 Apr 2026 19:02:55 -0400
Subject: [PATCH] Make `access` a 6809 norm; expose MO6 to SDL users.

---
 Analyser/Static/Thomson/Target.hpp |  8 --------
 Machines/Thomson/MO5/MO5.cpp       | 27 +++++----------------------
 Processors/6809/6809.hpp           | 27 ++++++++++++++++++++++++++-
 3 files changed, 31 insertions(+), 31 deletions(-)

diff --git a/Analyser/Static/Thomson/Target.hpp b/Analyser/Static/Thomson/Target.hpp
index dceefab3c..a8a0a0d6f 100644
--- a/Analyser/Static/Thomson/Target.hpp
+++ b/Analyser/Static/Thomson/Target.hpp
@@ -33,14 +33,6 @@ private:
 		DeclareField(floppy);
 		AnnounceEnum(Model);
 		DeclareField(model);
-
-		// TODO: eliminate this if/when MO6 emulation works.
-		limit_enum(
-			&model,
-			Model::MO5v1,
-			Model::MO5v11,
-			-1
-		);
 	}
 };
 
diff --git a/Machines/Thomson/MO5/MO5.cpp b/Machines/Thomson/MO5/MO5.cpp
index d21fca280..ad2caef60 100644
--- a/Machines/Thomson/MO5/MO5.cpp
+++ b/Machines/Thomson/MO5/MO5.cpp
@@ -112,27 +112,6 @@ struct ConcreteMachine:
 		audio_queue_.lock_flush();
 	}
 
-	template <
-		int address,
-		CPU::M6809::ReadWrite read_write,
-		typename ComponentT
-	>
-	static void access(ComponentT &component, CPU::M6809::data_t<read_write> value) {
-		if constexpr (CPU::M6809::is_read(read_write)) {
-			if constexpr (requires { component.operator->(); }) {
-				value = component->template read<address>();
-			} else {
-				value = component.template read<address>();
-			}
-		} else {
-			if constexpr (requires { component.operator->(); }) {
-				component->template write<address>(value);
-			} else {
-				component.template write<address>(value);
-			}
-		}
-	}
-
 	template <
 		CPU::M6809::BusPhase bus_phase,
 		CPU::M6809::LIC lic,
@@ -181,6 +160,9 @@ struct ConcreteMachine:
 				};
 
 				switch(address) {
+					// TODO: Is there a simpler way to use `namespace`?
+					using namespace CPU::M6809;
+
 					case 0xa7c0:	access<0xa7c0, read_write>(system_pia_, value);				break;
 					case 0xa7c1:	access<0xa7c1, read_write>(system_pia_, value);				break;
 					case 0xa7c2:	access<0xa7c2, read_write>(system_pia_, value);				break;
@@ -199,6 +181,7 @@ struct ConcreteMachine:
 
 					case 0xa7e4:	if(is_mo6) access<0xa7e4, read_write>(memory_, value); else unmapped();		break;
 
+					// TODO: consolidate below.
 					case 0xa7e5:
 						if constexpr (is_mo6) {
 							if(memory_.access_mode() == AccessMode::System) {
@@ -220,7 +203,7 @@ struct ConcreteMachine:
 								access<0xa7e6, read_write>(memory_, value);
 							} else {
 								if constexpr (CPU::M6809::is_read(read_write)) {
-									value = video_->horizontal_state();
+									access<0xa7e6, read_write>(video_, value);
 								} else {
 									memory_.template write<0xa7e6>(value);
 								}
diff --git a/Processors/6809/6809.hpp b/Processors/6809/6809.hpp
index ea1b7b674..7220022aa 100644
--- a/Processors/6809/6809.hpp
+++ b/Processors/6809/6809.hpp
@@ -95,7 +95,6 @@ static constexpr Timescale duration([[maybe_unused]] const BusPhase phase) {
 	}
 }
 
-
 enum class Line {
 	Halt,
 	DMABusReq,
@@ -157,6 +156,32 @@ using NoValue = Bus::Data::NoValue<uint8_t>;
 template <ReadWrite read_write>
 using data_t = Bus::Data::data_t<uint8_t, false, access_type(read_write)>;
 
+// MARK: - Bus-access helper.
+
+/*!
+	Interprets @c read_write to perform either a `read<address>` or a `write<address>` on `component`.
+*/
+template <
+	int address,
+	ReadWrite read_write,
+	typename ComponentT
+>
+static void access(ComponentT &component, CPU::M6809::data_t<read_write> value) {
+	if constexpr (CPU::M6809::is_read(read_write)) {
+		if constexpr (requires { component.operator->(); }) {
+			value = component->template read<address>();
+		} else {
+			value = component.template read<address>();
+		}
+	} else {
+		if constexpr (requires { component.operator->(); }) {
+			component->template write<address>(value);
+		} else {
+			component.template write<address>(value);
+		}
+	}
+}
+
 // MARK: - Code-generation choices.
 
 enum class PausePrecision {