From debdad350d80222815154bb0750ef0c550795c5d Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 2 Feb 2023 12:03:33 -0500
Subject: [PATCH] Don't allow a disabled screen to interfere with Yamaha
 addressing.

---
 Components/9918/Implementation/9918.cpp     |  9 +++++----
 Components/9918/Implementation/9918Base.hpp | 13 ++++++-------
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/Components/9918/Implementation/9918.cpp b/Components/9918/Implementation/9918.cpp
index 871a21bcc..730a4c639 100644
--- a/Components/9918/Implementation/9918.cpp
+++ b/Components/9918/Implementation/9918.cpp
@@ -308,7 +308,8 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
 
 				// Establish the current screen output mode, which will be captured as a
 				// line mode momentarily.
-				this->screen_mode_ = this->current_screen_mode();
+				this->screen_mode_ = this->template current_screen_mode<true>();
+				this->underlying_mode_ = this->template current_screen_mode<false>();
 
 				// Based on the output mode, pick a line mode.
 				next_line_buffer.first_pixel_output_column = Timing<personality>::FirstPixelCycle;
@@ -723,7 +724,7 @@ void Base<personality>::commit_register(int reg, uint8_t value) {
 				// b5: enable light pen interrupts
 				// b6: set colour bus to input or output mode
 
-				LOG("Screen mode: " << int(current_screen_mode()));
+				LOG("Screen mode: " << int(current_screen_mode<true>()));
 			break;
 
 			case 1:
@@ -733,7 +734,7 @@ void Base<personality>::commit_register(int reg, uint8_t value) {
 					((value & 0x08) >> 2)
 				);
 
-				LOG("Screen mode: " << int(current_screen_mode()));
+				LOG("Screen mode: " << int(current_screen_mode<true>()));
 			break;
 
 			case 8:
@@ -845,7 +846,7 @@ void Base<personality>::commit_register(int reg, uint8_t value) {
 					Storage<personality>::command_ &&
 					Storage<personality>::command_->access == Command::AccessType::WaitForColourReceipt
 				) {
-					Storage<personality>::command_->advance(pixels_per_byte(this->screen_mode_));
+					Storage<personality>::command_->advance(pixels_per_byte(this->underlying_mode_));
 					Storage<personality>::update_command_step(fetch_pointer_.column);
 				}
 			break;
diff --git a/Components/9918/Implementation/9918Base.hpp b/Components/9918/Implementation/9918Base.hpp
index abb85a747..01da6f176 100644
--- a/Components/9918/Implementation/9918Base.hpp
+++ b/Components/9918/Implementation/9918Base.hpp
@@ -543,7 +543,7 @@ template <Personality personality> struct Base: public Storage<personality> {
 	bool enable_line_interrupts_ = false;
 	bool line_interrupt_pending_ = false;
 
-	ScreenMode screen_mode_;
+	ScreenMode screen_mode_, underlying_mode_;
 	LineBuffer line_buffers_[313];
 	void posit_sprite(LineBuffer &buffer, int sprite_number, int sprite_y, int screen_row);
 
@@ -570,8 +570,8 @@ template <Personality personality> struct Base: public Storage<personality> {
 
 	void commit_register(int reg, uint8_t value);
 
-	ScreenMode current_screen_mode() const {
-		if(blank_display_) {
+	template <bool check_blank> ScreenMode current_screen_mode() const {
+		if(check_blank && blank_display_) {
 			return ScreenMode::Blank;
 		}
 
@@ -737,13 +737,13 @@ template <Personality personality> struct Base: public Storage<personality> {
 
 						ram_[address] = Storage<personality>::command_latch_;
 
-						Storage<personality>::command_->advance(pixels_per_byte(this->screen_mode_));
+						Storage<personality>::command_->advance(pixels_per_byte(this->underlying_mode_));
 						Storage<personality>::update_command_step(access_column);
 					} break;
 
 					case CommandStep::WriteByte:
 						ram_[command_address()] = Storage<personality>::command_context_.colour;
-						Storage<personality>::command_->advance(pixels_per_byte(this->screen_mode_));
+						Storage<personality>::command_->advance(pixels_per_byte(this->underlying_mode_));
 						Storage<personality>::update_command_step(access_column);
 					break;
 				}
@@ -756,8 +756,7 @@ template <Personality personality> struct Base: public Storage<personality> {
 		++ram_pointer_;
 
 		if constexpr (is_yamaha_vdp(personality)) {
-			const ScreenMode mode = current_screen_mode();
-			if(mode == ScreenMode::YamahaGraphics6 || mode == ScreenMode::YamahaGraphics7) {
+			if(this->underlying_mode_ == ScreenMode::YamahaGraphics6 || this->underlying_mode_ == ScreenMode::YamahaGraphics7) {
 				// Rotate address one to the right as the hardware accesses
 				// the underlying banks of memory alternately but presents
 				// them as if linear.