CLK/Components/9918/9918.cpp

//
//  9918.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 25/11/2017.
//  Copyright © 2017 Thomas Harte. All rights reserved.
//

#include "9918.hpp"

using namespace TI;

TMS9918::TMS9918(Personality p) :
	crt_(new Outputs::CRT::CRT(911, 1, Outputs::CRT::DisplayType::NTSC60, 3)) {
	crt_->set_rgb_sampling_function(
		"vec3 rgb_sample(usampler2D sampler, vec2 coordinate, vec2 icoordinate)"
		"{"
			"return texture(sampler, coordinate).rgb;"
		"}");
}

std::shared_ptr<Outputs::CRT::CRT> TMS9918::get_crt() {
	return crt_;
}

void TMS9918::run_for(const HalfCycles cycles) {
}

void TMS9918::set_register(int address, uint8_t value) {
	// Writes to address 0 are writes to the video RAM. Store
	// the value and return.
	if(!(address & 1)) {
		write_phase_ = false;
		read_ahead_buffer_ = value;
		ram_[ram_pointer_ & 16383] = value;
		ram_pointer_++;
		return;
	}

	// Writes to address 1 are performed in pairs; if this is the
	// low byte of a value, store it and wait for the high byte.
	if(!write_phase_) {
		low_write_ = value;
		write_phase_ = true;
		return;
	}

	write_phase_ = false;
	if(value & 0x80) {
		// This is a write to a register.
		switch(value & 7) {
			case 0:
				screen_mode_ = (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);
				sprites_16x16_ = !!(low_write_ & 0x02);
				sprites_magnified_ = !!(low_write_ & 0x01);
				reevaluate_interrupts();
			break;

			case 2:
				pattern_name_address_ = (low_write_ & 0xf) << 10;
			break;

			case 3:
				colour_table_address_ = low_write_ << 6;
			break;

			case 4:
				pattern_generator_table_address_ = (low_write_ & 0x07) << 11;
			break;

			case 5:
				sprite_attribute_table_address_ = (low_write_ & 0x7f) << 7;
			break;

			case 6:
				sprite_generator_table_address_ = (low_write_ & 0x07) << 11;
			break;

			case 7:
				text_colour_ = low_write_ >> 4;
				background_colour_ = low_write_ & 0xf;
			break;
		}
	} else {
		// This is a write to the RAM pointer.
		ram_pointer_ = static_cast<uint16_t>(low_write_ | (value << 8));
		if(!(value & 0x40)) {
			// Officially a 'read' set, so perform lookahead.
			read_ahead_buffer_ = ram_[ram_pointer_ & 16383];
			ram_pointer_++;
		}
	}
}

uint8_t TMS9918::get_register(int address) {
	write_phase_ = false;

	// Reads from address 0 read video RAM, via the read-ahead buffer.
	if(!(address & 1)) {
		uint8_t result = read_ahead_buffer_;
		read_ahead_buffer_ = ram_[ram_pointer_ & 16383];
		ram_pointer_++;
		return result;
	}

	// Reads from address 1 get the status register;
	uint8_t result = status_;
	status_ &= ~(0x80 | 0x20);
	reevaluate_interrupts();
	return result;
}

void TMS9918::reevaluate_interrupts() {
	
}