From b0d1dedb6506b528d3e8ee61d662a04d885b812d Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Mon, 4 Dec 2023 16:34:46 -0500
Subject: [PATCH] Support MDA control: display enable.

---
 Machines/PCCompatible/PCCompatible.cpp | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/Machines/PCCompatible/PCCompatible.cpp b/Machines/PCCompatible/PCCompatible.cpp
index 905dd7997..2a7750db7 100644
--- a/Machines/PCCompatible/PCCompatible.cpp
+++ b/Machines/PCCompatible/PCCompatible.cpp
@@ -478,7 +478,7 @@ class MDA {
 		template <int address>
 		void write(uint8_t value) {
 			if constexpr (address & 0x8) {
-				printf("TODO: write MDA control %02x\n", value);
+				outputter_.set_control(value);
 			} else {
 				if constexpr (address & 0x1) {
 					crtc_.set_register(value);
@@ -491,8 +491,7 @@ class MDA {
 		template <int address>
 		uint8_t read() {
 			if constexpr (address & 0x8) {
-				printf("TODO: read MDA control\n");
-				return 0xff;
+				return outputter_.control();
 			} else {
 				return crtc_.get_register();
 			}
@@ -519,11 +518,22 @@ class MDA {
 				crt.set_display_type(Outputs::Display::DisplayType::RGB);
 			}
 
+			void set_control(uint8_t control) {
+				// b0: 'high resolution' (probably breaks if not 1)
+				// b3: video enable
+				// b5: enable blink
+				control_ = control;
+			}
+
+			uint8_t control() {
+				return control_;
+			}
+
 			void perform_bus_cycle_phase1(const Motorola::CRTC::BusState &state) {
 				// Determine new output state.
 				const OutputState new_state =
 					(state.hsync | state.vsync) ? OutputState::Sync :
-						(state.display_enable ? OutputState::Pixels : OutputState::Border);
+						((state.display_enable && control_&0x08) ? OutputState::Pixels : OutputState::Border);
 
 				// Upon either a state change or just having accumulated too much local time...
 				if(new_state != output_state || count > 882) {
@@ -585,6 +595,8 @@ class MDA {
 								break;
 							}
 
+							// TODO: blink.
+
 							if(((attributes & 7) == 1) && state.row_address == 13) {
 								// Draw as underline.
 								std::fill(pixel_pointer, pixel_pointer + 9, intensity);
@@ -631,6 +643,8 @@ class MDA {
 
 			const uint8_t *ram = nullptr;
 			std::vector<uint8_t> font;
+
+			uint8_t control_ = 0;
 		} outputter_;
 		Motorola::CRTC::CRTC6845<CRTCOutputter, Motorola::CRTC::CursorType::MDA> crtc_;
 
@@ -942,6 +956,8 @@ class IO {
 				case 0x03f4:	return fdc_.status();
 				case 0x03f5:	return fdc_.read();
 
+				case 0x03b8:	return mda_.read<8>();
+
 				case 0x02e8:	case 0x02e9:	case 0x02ea:	case 0x02eb:
 				case 0x02ec:	case 0x02ed:	case 0x02ee:	case 0x02ef:
 				case 0x02f8:	case 0x02f9:	case 0x02fa:	case 0x02fb: