From 794adf470bb654749db1209e892e91a2b3adce1c Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sun, 8 Jan 2023 21:25:22 -0500
Subject: [PATCH] Break assumption that cycles = pixels; fix pixel clocking.

---
 Components/9918/Implementation/9918.cpp       | 16 +++++++-----
 .../9918/Implementation/ClockConverter.hpp    | 25 ++++++++++++++++---
 Machines/MSX/MSX.cpp                          |  2 +-
 3 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/Components/9918/Implementation/9918.cpp b/Components/9918/Implementation/9918.cpp
index 3c47a6878..dd447d963 100644
--- a/Components/9918/Implementation/9918.cpp
+++ b/Components/9918/Implementation/9918.cpp
@@ -417,23 +417,25 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
 						line_buffer.next_border_column,
 						if(!this->asked_for_write_area_) {
 							this->asked_for_write_area_ = true;
+
+							// TODO: how many pixels across is this mode?
 							this->pixel_origin_ = this->pixel_target_ = reinterpret_cast<uint32_t *>(
-								this->crt_.begin_data(size_t(line_buffer.next_border_column - line_buffer.first_pixel_output_column))
+								this->crt_.begin_data(256)
 							);
 						}
 
 						if(this->pixel_target_) {
 							switch(line_buffer.line_mode) {
-								case LineMode::SMS:			draw(draw_sms(relative_start, relative_end, cram_value), to_tms_access_clock);	break;
-								case LineMode::Character:	draw(draw_tms_character(relative_start, relative_end), to_tms_access_clock);	break;
-								case LineMode::Text:		draw(draw_tms_text(relative_start, relative_end), to_tms_access_clock);			break;
+								case LineMode::SMS:			draw(draw_sms(relative_start, relative_end, cram_value), to_tms_pixel_clock);	break;
+								case LineMode::Character:	draw(draw_tms_character(relative_start, relative_end), to_tms_pixel_clock);		break;
+								case LineMode::Text:		draw(draw_tms_text(relative_start, relative_end), to_tms_pixel_clock);			break;
 
 								case LineMode::Refresh:		break;	/* Dealt with elsewhere. */
 							}
 						}
 
 						if(end == line_buffer.next_border_column) {
-							const int length = line_buffer.next_border_column - line_buffer.first_pixel_output_column;
+							const int length = 256;//line_buffer.next_border_column - line_buffer.first_pixel_output_column;	// TODO: proper number of pixels, as above.
 							this->crt_.output_data(this->clock_converter_.to_crt_clock(length), size_t(length));
 							this->pixel_origin_ = this->pixel_target_ = nullptr;
 							this->asked_for_write_area_ = false;
@@ -713,7 +715,9 @@ HalfCycles TMS9918<personality>::get_next_sequence_point() const {
 		) % frame_length;
 	if(!time_until_frame_interrupt) time_until_frame_interrupt = frame_length;
 
-	if(!this->enable_line_interrupts_) return this->clock_converter_.half_cycles_before_internal_cycles(time_until_frame_interrupt);
+	if(!this->enable_line_interrupts_) {
+		return this->clock_converter_.half_cycles_before_internal_cycles(time_until_frame_interrupt);
+	}
 
 	// Calculate when the next line interrupt will occur.
 	int next_line_interrupt_row = -1;
diff --git a/Components/9918/Implementation/ClockConverter.hpp b/Components/9918/Implementation/ClockConverter.hpp
index ab1b438cf..f6ae33bd5 100644
--- a/Components/9918/Implementation/ClockConverter.hpp
+++ b/Components/9918/Implementation/ClockConverter.hpp
@@ -155,7 +155,7 @@ template <Personality personality> class ClockConverter {
 
 				case Personality::V9938:
 				case Personality::V9958:
-					return HalfCycles(internal_cycles / 3);
+					return HalfCycles((internal_cycles + 2) / 3);
 
 				case Personality::MDVDP:
 					return HalfCycles(
@@ -166,8 +166,7 @@ template <Personality personality> class ClockConverter {
 
 		/*!
 			Converts a position in internal cycles to its corresponding position
-			on the TMS memory-access clock, i.e. scales down to 171 clocks
-			per line
+			on the TMS memory-access clock, i.e. scales to 171 clocks per line.
 		*/
 		static constexpr int to_tms_access_clock(int source) {
 			switch(personality) {
@@ -183,6 +182,24 @@ template <Personality personality> class ClockConverter {
 			}
 		}
 
+		/*!
+			Converts a position in internal cycles to its corresponding position
+			on the TMS pixel clock, i.e. scales to 342 clocks per line.
+		*/
+		static constexpr int to_tms_pixel_clock(int source) {
+			switch(personality) {
+				default:
+				return source;
+
+				case Personality::V9938:
+				case Personality::V9958:
+				return source >> 2;
+
+				case Personality::MDVDP:
+				return source / 10;
+			}
+		}
+
 		/*!
 			Convers a position in internal cycles to its corresponding position
 			on the CRT's output clock, which [TODO] is clocked so that
@@ -191,7 +208,7 @@ template <Personality personality> class ClockConverter {
 		static constexpr int to_crt_clock(int source) {
 			switch(personality) {
 				default:
-				return source * 4;
+				return source << 2;
 
 				case Personality::V9938:
 				case Personality::V9958:
diff --git a/Machines/MSX/MSX.cpp b/Machines/MSX/MSX.cpp
index 6bc06bda0..2ec502788 100644
--- a/Machines/MSX/MSX.cpp
+++ b/Machines/MSX/MSX.cpp
@@ -743,7 +743,7 @@ class ConcreteMachine:
 		};
 
 		CPU::Z80::Processor<ConcreteMachine, false, false> z80_;
-		JustInTimeActor<TI::TMS::TMS9918<TI::TMS::Personality::TMS9918A>> vdp_;
+		JustInTimeActor<TI::TMS::TMS9918<TI::TMS::Personality::V9938>> vdp_;
 		Intel::i8255::i8255<i8255PortHandler> i8255_;
 
 		Concurrency::AsyncTaskQueue<false> audio_queue_;