Adds the absolute most basic version of in-frame time keeping, to display a white square.

Components/9918/9918.cpp

@@ -11,7 +11,7 @@
 using namespace TI;
 
 TMS9918::TMS9918(Personality p) :
-	crt_(new Outputs::CRT::CRT(911, 1, Outputs::CRT::DisplayType::NTSC60, 3)) {
+	crt_(new Outputs::CRT::CRT(342, 1, Outputs::CRT::DisplayType::NTSC60, 4)) {
 	crt_->set_rgb_sampling_function(
 		"vec3 rgb_sample(usampler2D sampler, vec2 coordinate, vec2 icoordinate)"
 		"{"
@@ -24,8 +24,75 @@ std::shared_ptr<Outputs::CRT::CRT> TMS9918::get_crt() {
 }
 
 void TMS9918::run_for(const HalfCycles cycles) {
+	// TODO: all video output (!)
+
+	// As specific as I've been able to get:
+	// Scanline time is always 227.75 cycles.
+	// PAL output is 313 lines total. NTSC output is 262 lines total.
+	// Interrupt is signalled upon entering the lower border.
+
+	// Convert to 342 cycles per line; the internal clock is 1.5 times the
+	// nominal 3.579545 Mhz that I've advertised for this part.
+	int int_cycles = (cycles.as_int() * 3) + cycles_error_;
+	cycles_error_ = int_cycles & 3;
+	int_cycles >>= 2;
+
+	//
+	// Break that down as:
+	// 26 cycles sync;
+
+	while(int_cycles) {
+		int cycles_left = std::min(342 - column_, int_cycles);
+		int end_column = std::min(column_ + int_cycles, 342);
+		if(row_	< 192) {
+			// Pixels.
+			if(column_ < 26 && end_column >= 26) {
+				crt_->output_sync(static_cast<unsigned int>(26));
+				column_ = 26;
+			}
+			if(column_ >= 26 && end_column >= 69) {	// TODO: modes other than text
+				crt_->output_blank(static_cast<unsigned int>(69 - 26));
+				column_ = 69;
+				pixel_target_ = crt_->allocate_write_area(256);
+			}
+			while(column_ < end_column && column_ < 309) {	// TODO: modes other than text
+				pixel_target_[0] = pixel_target_[1] = pixel_target_[2] = pixel_target_[3] = 0xff;
+				pixel_target_ += 4;
+				column_ ++;
+			}
+			if(column_ == 309 && end_column > 309) {
+				crt_->output_data(240, 1);	// TODO: modes other than text
+			}
+			if(end_column == 342) {
+				crt_->output_blank(static_cast<unsigned int>(342 - 309));
+			}
+		} else if(row_ >= 227 && row_ < 230) {	// TODO: don't hard-code NTSC.
+			// Vertical sync.
+			crt_->output_sync(static_cast<unsigned int>(cycles_left));
+		} else {
+			// Blank.
+			if(column_ < 26 && end_column >= 26) {
+				crt_->output_sync(static_cast<unsigned int>(26));
+				column_ = 26;
+			}
+			if(column_ < end_column) {
+				crt_->output_blank(static_cast<unsigned int>(end_column - column_));
+				column_ = end_column;
+			}
+		}
+
+		int_cycles += cycles_left;
+		column_ = end_column;
+		if(column_ == 342) {
+			column_ = 0;
+			row_ = (row_ + 1) % 262;	// TODO: don't hard-code NTSC.
+			// TODO: consider triggering an interrupt here.
+		}
+	}
 }
 
+// TODO: as a temporary development measure, memory access below is magically instantaneous. Correct that.
+
 void TMS9918::set_register(int address, uint8_t value) {
 	// Writes to address 0 are writes to the video RAM. Store
 	// the value and return.
@@ -50,36 +117,36 @@ void TMS9918::set_register(int address, uint8_t value) {
 		// This is a write to a register.
 		switch(value & 7) {
 			case 0:
-				screen_mode_ = (screen_mode_ & 6) | ((low_write_ & 2) >> 1);
+				next_screen_mode_ = (next_screen_mode_ & 6) | ((low_write_ & 2) >> 1);
 			break;
 
 			case 1:
 				blank_screen_ = !!(low_write_ & 0x40);
 				generate_interrupts_ = !!(low_write_ & 0x20);
-				screen_mode_ = (screen_mode_ & 1) | ((low_write_ & 0x18) >> 3);
+				next_screen_mode_ = (screen_mode_ & 1) | ((low_write_ & 0x18) >> 3);
 				sprites_16x16_ = !!(low_write_ & 0x02);
 				sprites_magnified_ = !!(low_write_ & 0x01);
 				reevaluate_interrupts();
 			break;
 
 			case 2:
-				pattern_name_address_ = (low_write_ & 0xf) << 10;
+				pattern_name_address_ = static_cast<uint16_t>((low_write_ & 0xf) << 10);
 			break;
 
 			case 3:
-				colour_table_address_ = low_write_ << 6;
+				colour_table_address_ = static_cast<uint16_t>(low_write_ << 6);
 			break;
 
 			case 4:
-				pattern_generator_table_address_ = (low_write_ & 0x07) << 11;
+				pattern_generator_table_address_ = static_cast<uint16_t>((low_write_ & 0x07) << 11);
 			break;
 
 			case 5:
-				sprite_attribute_table_address_ = (low_write_ & 0x7f) << 7;
+				sprite_attribute_table_address_ = static_cast<uint16_t>((low_write_ & 0x7f) << 7);
 			break;
 
 			case 6:
-				sprite_generator_table_address_ = (low_write_ & 0x07) << 11;
+				sprite_generator_table_address_ = static_cast<uint16_t>((low_write_ & 0x07) << 11);
 			break;
 
 			case 7:

Components/9918/9918.hpp

@@ -42,7 +42,7 @@ class TMS9918 {
 	private:
 		std::shared_ptr<Outputs::CRT::CRT> crt_;
 	
-		uint16_t ram_[16384];
+		uint8_t ram_[16384];
 
 		uint16_t ram_pointer_ = 0;
 		uint8_t read_ahead_buffer_ = 0;
@@ -53,7 +53,7 @@ class TMS9918 {
 		uint8_t low_write_ = 0;
 
 		// The various register flags.
-		int screen_mode_ = 0;
+		int next_screen_mode_ = 0, screen_mode_ = 0;
 		bool blank_screen_ = true;
 		bool sprites_16x16_ = false;
 		bool sprites_magnified_ = false;
@@ -67,6 +67,10 @@ class TMS9918 {
 		uint8_t background_colour_ = 0;
 
 		void reevaluate_interrupts();
+
+		int column_ = 0, row_ = 0;
+		int cycles_error_ = 0;
+		uint8_t *pixel_target_ = nullptr;
 };
 
 };