CLK/Components/RP5C01/RP5C01.cpp

//
//  RP5C01.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 14/01/2023.
//  Copyright © 2023 Thomas Harte. All rights reserved.
//

#include "RP5C01.hpp"

#include "../../Numeric/NumericCoder.hpp"

#include <ctime>

using namespace Ricoh::RP5C01;

RP5C01::RP5C01(HalfCycles clock_rate) : clock_rate_(clock_rate) {
	// Seed internal clock.
	std::time_t now = std::time(NULL);
	std::tm *time_date = std::localtime(&now);

	seconds_ =
		time_date->tm_sec +
		time_date->tm_min * 60 +
		time_date->tm_hour * 60 * 60;

	day_of_the_week_ = time_date->tm_wday;
	day_ = time_date->tm_mday;
	month_ = time_date->tm_mon;
	year_ = (time_date->tm_year + 20) % 100;	// This is probably MSX specific; rethink if/when other machines use this chip.
	leap_year_ = time_date->tm_year % 4;
}

void RP5C01::run_for(HalfCycles cycles) {
	sub_seconds_ += cycles;

	// Guess: this happens so rarely (i.e. once a second, ordinarily) that
	// it's not worth worrying about the branch prediction consequences.
	//
	// ... and ditto all the conditionals below, which will be very rarely reached.
	if(sub_seconds_ < clock_rate_) {
		return;
	}
	const auto elapsed_seconds = int(sub_seconds_.as_integral() / clock_rate_.as_integral());
	sub_seconds_ %= clock_rate_;

	// Update time within day.
	seconds_ += elapsed_seconds;

	constexpr int day_length = 60 * 60 * 24;
	if(seconds_ < day_length) {
		return;
	}
	const int elapsed_days = seconds_ / day_length;
	seconds_ %= day_length;

	// Day of the week doesn't aggregate upwards.
	day_of_the_week_ = (day_of_the_week_ + elapsed_days) % 7;

	// Assumed for now: day and month run from 0.
	// A leap year count of 0 implies a leap year.
	// TODO: verify.
	day_ += elapsed_days;
	while(true) {
		int month_length = 1;
		switch(month_) {
			default:
			case 0:	month_length = 31;					break;
			case 1:	month_length = 28 + !leap_year_;	break;
			case 2: month_length = 31;					break;
			case 3: month_length = 30;					break;
			case 4: month_length = 31;					break;
			case 5: month_length = 30;					break;
			case 6: month_length = 31;					break;
			case 7: month_length = 31;					break;
			case 8: month_length = 30;					break;
			case 9: month_length = 31;					break;
			case 10: month_length = 30;					break;
			case 11: month_length = 31;					break;
		}

		if(day_ < month_length) {
			return;
		}

		day_ -= month_length;
		++month_;

		if(month_ == 12) {
			month_ = 0;
			year_ = (year_ + 1) % 100;
			leap_year_ = (leap_year_ + 1) & 3;
		}
	}
}

namespace {

constexpr int Reg(int mode, int address) {
	return address | mode << 4;
}

constexpr int PM = 1 << 4;

constexpr int twenty_four_to_twelve(int hours) {
	switch(hours) {
		default:	return (hours % 12) + (hours > 12 ? PM : 0);
		case 0:		return 12;
		case 12:	return 12 | PM;
	}
}

constexpr int twelve_to_twenty_four(int hours) {
	hours = (hours & 0xf) + (hours & PM ? 12 : 0);
	switch(hours) {
		default:	break;
		case 24:	return 12;
		case 12:	return 0;
	}
	return hours;
}

using SecondEncoder = Numeric::NumericCoder<
	10, 6,	// Seconds.
	10, 6,	// Minutes.
	24		// Hours
>;
using TwoDigitEncoder = Numeric::NumericCoder<10, 10>;

}

/// Performs a write of @c value to @c address.
void RP5C01::write(int address, uint8_t value) {
	address &= 0xf;
	value &= 0xf;

	// Handle potential RAM accesses.
	if(address < 0xd && mode_ >= 2) {
		address += mode_ == 3 ? 13 : 0;
		ram_[size_t(address)] = value & 0xf;
		return;
	}

	switch(Reg(mode_, address)) {
		default: break;

		// Seconds.
		case Reg(0, 0x00):	SecondEncoder::encode<0>(seconds_, value);		break;
		case Reg(0, 0x01):	SecondEncoder::encode<1>(seconds_, value);		break;

		// Minutes.
		case Reg(0, 0x02):	SecondEncoder::encode<2>(seconds_, value);		break;
		case Reg(0, 0x03):	SecondEncoder::encode<3>(seconds_, value);		break;

		// Hours.
		case Reg(0, 0x04):
		case Reg(0, 0x05): {
			int hours = SecondEncoder::decode<4>(seconds_);
			if(!twentyfour_hour_clock_) {
				hours = twenty_four_to_twelve(hours);
			}
			if(address == 0x4) {
				TwoDigitEncoder::encode<0>(hours, value);
			} else {
				TwoDigitEncoder::encode<1>(hours, value & 3);
			}
			if(!twentyfour_hour_clock_) {
				hours = twelve_to_twenty_four(hours);
			}
			SecondEncoder::encode<4>(seconds_, hours);
		} break;

		// Day of the week.
		case Reg(0, 0x06):	day_of_the_week_ = value % 7;							break;

		// Day.
		case Reg(0, 0x07):	TwoDigitEncoder::encode<0>(day_, value);				break;
		case Reg(0, 0x08):	TwoDigitEncoder::encode<1>(day_, value & 3);			break;

		// Month.
		case Reg(0, 0x09):	TwoDigitEncoder::encode<0>(month_, (value - 1));		break;
		case Reg(0, 0x0a):	TwoDigitEncoder::encode<1>(month_, (value - 1) & 1);	break;

		// Year.
		case Reg(0, 0x0b):	TwoDigitEncoder::encode<0>(year_, value);				break;
		case Reg(0, 0x0c):	TwoDigitEncoder::encode<1>(year_, value);				break;

		// TODO: alarm minutes.
		case Reg(1, 0x02):
		case Reg(1, 0x03):	break;

		// TODO: alarm hours.
		case Reg(1, 0x04):
		case Reg(1, 0x05):	break;

		// TODO: alarm day-of-the-week.
		case Reg(1, 0x06):	break;

		// TODO: alarm day.
		case Reg(1, 0x07):
		case Reg(1, 0x08):	break;

		// 24/12-hour clock.
		case Reg(1, 0x0a):
			twentyfour_hour_clock_ = value & 1;
		break;

		// Lead-year counter.
		case Reg(1, 0x0b):
			leap_year_ = value & 3;
		break;

		//
		// Registers D–F don't depend on the mode.
		//

		case Reg(0, 0xd):	case Reg(1, 0xd):	case Reg(2, 0xd):	case Reg(3, 0xd):
			timer_enabled_ = value & 0x8;
			alarm_enabled_ = value & 0x4;
			mode_ = value & 0x3;
		break;
		case Reg(0, 0xe):	case Reg(1, 0xe):	case Reg(2, 0xe):	case Reg(3, 0xe):
			// Test register; unclear what is supposed to happen.
		break;
		case Reg(0, 0xf):	case Reg(1, 0xf):	case Reg(2, 0xf):	case Reg(3, 0xf):
			one_hz_on_ = !(value & 0x8);
			sixteen_hz_on_ = !(value & 0x4);
			// TODO: b0 = alarm reset; b1 = timer reset.
		break;
	}

}

uint8_t RP5C01::read(int address) {
	address &= 0xf;

	if(address < 0xd && mode_ >= 2) {
		address += mode_ == 3 ? 13 : 0;
		return 0xf0 | ram_[size_t(address)];
	}

	int value = 0xf;
	switch(Reg(mode_, address)) {
		// Second.
		case Reg(0, 0x00):	value = SecondEncoder::decode<0>(seconds_);	break;
		case Reg(0, 0x01):	value = SecondEncoder::decode<1>(seconds_);	break;

		// Minute.
		case Reg(0, 0x02):	value = SecondEncoder::decode<2>(seconds_);	break;
		case Reg(0, 0x03):	value = SecondEncoder::decode<3>(seconds_);	break;

		// Hour.
		case Reg(0, 0x04):
		case Reg(0, 0x05): {
			int hours = SecondEncoder::decode<4>(seconds_);
			if(!twentyfour_hour_clock_) {
				hours = twenty_four_to_twelve(hours);
			}
			if(address == 0x4) {
				value = TwoDigitEncoder::decode<0>(hours);
			} else {
				value = TwoDigitEncoder::decode<1>(hours);
			}
		} break;

		// Day-of-the-week.
		case Reg(0, 0x06):	value = day_of_the_week_;	break;

		// Day.
		case Reg(0, 0x07):	value = TwoDigitEncoder::decode<0>(day_);		break;
		case Reg(0, 0x08):	value = TwoDigitEncoder::decode<1>(day_);		break;

		// Month.
		case Reg(0, 0x09):	value = TwoDigitEncoder::decode<0>(month_ + 1);	break;
		case Reg(0, 0x0a):	value = TwoDigitEncoder::decode<1>(month_ + 1);	break;

		// Year.
		case Reg(0, 0x0b):	value = TwoDigitEncoder::decode<0>(year_);		break;
		case Reg(0, 0x0c):	value = TwoDigitEncoder::decode<1>(year_);		break;

		// TODO: alarm minutes.
		case Reg(1, 0x02):
		case Reg(1, 0x03):	break;

		// TODO: alarm hours.
		case Reg(1, 0x04):
		case Reg(1, 0x05):	break;

		// TODO: alarm day-of-the-week.
		case Reg(1, 0x06):	break;

		// TODO: alarm day.
		case Reg(1, 0x07):
		case Reg(1, 0x08):	break;

		// 12/24-hour clock.
		case Reg(1, 0x0a):	value = twentyfour_hour_clock_;	break;

		// Leap year.
		case Reg(1, 0x0b):	value = leap_year_;				break;

		//
		// Registers D–F don't depend on the mode.
		//

		case Reg(0, 0xd):	case Reg(1, 0xd):	case Reg(2, 0xd):	case Reg(3, 0xd):
			value =
				(timer_enabled_ ? 0x8 : 0x0) |
				(alarm_enabled_ ? 0x4 : 0x0) |
				mode_;
		break;
		case Reg(0, 0xe):	case Reg(1, 0xe):	case Reg(2, 0xe):	case Reg(3, 0xe):
			// Test register; unclear what is supposed to happen.
		break;
		case Reg(0, 0xf):	case Reg(1, 0xf):	case Reg(2, 0xf):	case Reg(3, 0xf):
			value =
				(one_hz_on_ ? 0x0 : 0x8) |
				(sixteen_hz_on_ ? 0x0 : 0x4);
		break;
	}

	return uint8_t(0xf0 | value);
}