From 2913368a0601a6dcc83d97b252fc63f6cbf77d3d Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Wed, 8 Mar 2023 23:12:02 -0500
Subject: [PATCH] Attempt YMMM.

---
 Components/9918/Implementation/9918.cpp           |  6 +++---
 Components/9918/Implementation/9918Base.hpp       | 10 +++++++---
 Components/9918/Implementation/YamahaCommands.hpp |  2 ++
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/Components/9918/Implementation/9918.cpp b/Components/9918/Implementation/9918.cpp
index 8466e66ce..a3e2ff7fe 100644
--- a/Components/9918/Implementation/9918.cpp
+++ b/Components/9918/Implementation/9918.cpp
@@ -930,12 +930,12 @@ void Base<personality>::commit_register(int reg, uint8_t value) {
 					case 0b1000:	Begin(LogicalFill);					break;	// LMMV [logical move, VDP to VRAM, i.e. solid-colour fill].
 					case 0b1001:	Begin(Move<MoveType::Logical>);		break;	// LMMM [logical move, VRAM to VRAM].
 					case 0b1010:	break;	// TODO: lmcm.	[logical move, VRAM to CPU]
-					case 0b1011:	Begin(MoveFromCPU<true>);			break;	// LMMC	[logical move, CPU to VRAM].
+					case 0b1011:	Begin(MoveFromCPU<true>);			break;	// LMMC [logical move, CPU to VRAM].
 
 					case 0b1100:	Begin(HighSpeedFill);				break;	// HMMV [high-speed move, VDP to VRAM, i.e. single-byte fill].
 					case 0b1101:	Begin(Move<MoveType::HighSpeed>);	break;	// HMMM [high-speed move, VRAM to VRAM].
-					case 0b1110:	break;	// TODO: ymmm.	[high-speed move, y only, VRAM to VRAM]
-					case 0b1111:	Begin(MoveFromCPU<false>);			break;	// HMMC	[high-speed move, CPU to VRAM].
+					case 0b1110:	Begin(Move<MoveType::YOnly>);		break;	// YMMM [high-speed move, y only, VRAM to VRAM].
+					case 0b1111:	Begin(MoveFromCPU<false>);			break;	// HMMC [high-speed move, CPU to VRAM].
 				}
 #undef Begin
 
diff --git a/Components/9918/Implementation/9918Base.hpp b/Components/9918/Implementation/9918Base.hpp
index c0532805f..88983a646 100644
--- a/Components/9918/Implementation/9918Base.hpp
+++ b/Components/9918/Implementation/9918Base.hpp
@@ -440,12 +440,16 @@ template <Personality personality> struct Base: public Storage<personality> {
 						Storage<personality>::update_command_step(access_column);
 					} break;
 
-					case CommandStep::ReadSourceByte:
-						context.latched_colour.set(source[command_address(context.source, context.arguments & 0x10)]);
+					case CommandStep::ReadSourceByte: {
+						Vector source_vector = context.source;
+						if(Storage<personality>::command_->y_only) {
+							source_vector.v[0] = context.destination.v[0];
+						}
+						context.latched_colour.set(source[command_address(source_vector, context.arguments & 0x10)]);
 
 						Storage<personality>::minimum_command_column_ = access_column + 24;
 						Storage<personality>::next_command_step_ = CommandStep::WriteByte;
-					break;
+					} break;
 
 					case CommandStep::WriteByte:
 						destination[command_address(context.destination, context.arguments & 0x20)] = context.latched_colour.has_value() ? context.latched_colour.colour : context.colour.colour;
diff --git a/Components/9918/Implementation/YamahaCommands.hpp b/Components/9918/Implementation/YamahaCommands.hpp
index b684bb27a..f3e7349af 100644
--- a/Components/9918/Implementation/YamahaCommands.hpp
+++ b/Components/9918/Implementation/YamahaCommands.hpp
@@ -118,6 +118,7 @@ struct Command {
 	AccessType access = AccessType::PlotPoint;
 	int cycles = 0;
 	bool is_cpu_transfer = false;
+	bool y_only = false;
 
 	/// Current command parameters.
 	CommandContext &context;
@@ -342,6 +343,7 @@ template <MoveType type> struct Move: public Rectangle<type == MoveType::Logical
 	Move(CommandContext &context) : Rectangle(context) {
 		Command::access = is_logical ? Command::AccessType::CopyPoint : Command::AccessType::CopyByte;
 		Command::cycles = is_y_only ? 0 : 64;
+		Command::y_only = is_y_only;
 	}
 
 	void advance(int pixels_per_byte) final {