From 22b4b4d4e30b740e54c3913a05c9e6453eaed696 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Tue, 9 Jan 2024 22:03:24 -0500
Subject: [PATCH] Switch to named values for everything except blink mode.

---
 Components/6845/CRTC6845.hpp | 54 ++++++++++++++++++++++++++++++++----
 1 file changed, 49 insertions(+), 5 deletions(-)

diff --git a/Components/6845/CRTC6845.hpp b/Components/6845/CRTC6845.hpp
index 24c30f2c1..77f7e72c7 100644
--- a/Components/6845/CRTC6845.hpp
+++ b/Components/6845/CRTC6845.hpp
@@ -105,6 +105,14 @@ template <class BusHandlerT, Personality personality, CursorType cursor_type> cl
 		void set_register(uint8_t value) {
 			static constexpr bool is_ega = is_egavga(personality);
 
+			auto load_low = [value](uint16_t &target) {
+				target = (target & 0xff00) | value;
+			};
+			auto load_high = [value](uint16_t &target) {
+				constexpr uint8_t mask = RefreshMask >> 8;
+				target = uint16_t((target & 0x00ff) | ((value & mask) << 8));
+			};
+
 			switch(selected_register_) {
 				case 0:	layout_.horizontal.total = value;		break;
 				case 1: layout_.horizontal.displayed = value;	break;
@@ -127,6 +135,25 @@ template <class BusHandlerT, Personality personality, CursorType cursor_type> cl
 				case 5:	layout_.vertical.adjust = value & 0x1f;		break;
 				case 6:	layout_.vertical.displayed = value & 0x7f;	break;
 				case 7:	layout_.vertical.start_sync = value & 0x7f;	break;
+				case 8:
+					switch(value & 3) {
+						default:	layout_.interlace_mode_ = InterlaceMode::Off;					break;
+						case 0b01:	layout_.interlace_mode_ = InterlaceMode::InterlaceSync;			break;
+						case 0b11:	layout_.interlace_mode_ = InterlaceMode::InterlaceSyncAndVideo;	break;
+					}
+				break;
+				case 9:	layout_.vertical.end_row = value & 0x1f;	break;
+				case 10:
+					layout_.vertical.start_cursor = value & 0x1f;
+					// TODO: blink mode.
+				break;
+				case 11:
+					layout_.vertical.end_cursor = value & 0x1f;
+				break;
+				case 12:	load_high(layout_.start_address);	break;
+				case 13:	load_low(layout_.start_address);	break;
+				case 14:	load_high(layout_.cursor_address);	break;
+				case 15:	load_low(layout_.cursor_address);	break;
 			}
 
 			static constexpr uint8_t masks[] = {
@@ -181,7 +208,7 @@ template <class BusHandlerT, Personality personality, CursorType cursor_type> cl
 				bus_state_.refresh_address = (bus_state_.refresh_address + 1) & RefreshMask;
 
 				bus_state_.cursor = is_cursor_line_ &&
-					bus_state_.refresh_address == (registers_[15] | (registers_[14] << 8));
+					bus_state_.refresh_address == layout_.cursor_address;
 
 				// Check for end-of-line.
 				if(character_counter_ == layout_.horizontal.total) {
@@ -242,7 +269,7 @@ template <class BusHandlerT, Personality personality, CursorType cursor_type> cl
 			if constexpr (cursor_type != CursorType::None) {
 				// Check for cursor disable.
 				// TODO: this is handled differently on the EGA, should I ever implement that.
-				is_cursor_line_ &= bus_state_.row_address != (registers_[11] & 0x1f);
+				is_cursor_line_ &= bus_state_.row_address != layout_.vertical.end_cursor;
 			}
 
 			// Check for end of vertical sync.
@@ -269,7 +296,7 @@ template <class BusHandlerT, Personality personality, CursorType cursor_type> cl
 				}
 			} else {
 				// Advance vertical counter.
-				if(bus_state_.row_address == registers_[9]) {
+				if(bus_state_.row_address == layout_.vertical.end_row) {
 					bus_state_.row_address = 0;
 					line_address_ = end_of_line_address_;
 
@@ -306,7 +333,7 @@ template <class BusHandlerT, Personality personality, CursorType cursor_type> cl
 
 			if constexpr (cursor_type != CursorType::None) {
 				// Check for cursor enable.
-				is_cursor_line_ |= bus_state_.row_address == (registers_[10] & 0x1f);
+				is_cursor_line_ |= bus_state_.row_address == layout_.vertical.start_cursor;
 
 				switch(cursor_type) {
 					// MDA-style blinking.
@@ -328,7 +355,7 @@ template <class BusHandlerT, Personality personality, CursorType cursor_type> cl
 		inline void do_end_of_frame() {
 			line_counter_ = 0;
 			line_is_visible_ = true;
-			line_address_ = uint16_t((registers_[12] << 8) | registers_[13]);
+			line_address_ = layout_.start_address;
 			bus_state_.refresh_address = line_address_;
 			++bus_state_.field_count;
 		}
@@ -336,6 +363,14 @@ template <class BusHandlerT, Personality personality, CursorType cursor_type> cl
 		BusHandlerT &bus_handler_;
 		BusState bus_state_;
 
+		enum class InterlaceMode {
+			Off,
+			InterlaceSync,
+			InterlaceSyncAndVideo,
+		};
+		enum class BlinkMode {
+			// TODO.
+		};
 		struct {
 			struct {
 				uint8_t total;
@@ -350,7 +385,16 @@ template <class BusHandlerT, Personality personality, CursorType cursor_type> cl
 				uint8_t start_sync;
 				uint8_t sync_lines;
 				uint8_t adjust;
+
+				uint8_t end_row;
+				uint8_t start_cursor;
+				uint8_t end_cursor;
 			} vertical;
+
+			InterlaceMode interlace_mode_ = InterlaceMode::Off;
+			uint16_t start_address;
+			uint16_t cursor_address;
+			uint16_t light_pen_address;
 		} layout_;
 
 		uint8_t registers_[18]{};