EightBit/MC6850/src/MC6850.cpp

<EFBFBD><EFBFBD>#include "pch.h"
#include "MC6850.h"

#include <cassert>

bool EightBit::mc6850::selected() {
	return
			(CS0() == PinLevel::High)
		&&	(CS1() == PinLevel::High)
		&&	(CS2() == PinLevel::Low);
}

void EightBit::mc6850::reset() {
	if (m_firstMasterReset)
		IRQ() = RTS() = PinLevel::High;
	status() = 0;
	m_firstMasterReset = false;
}

void EightBit::mc6850::step(int cycles) {
	for (int i = 0; i < cycles; ++i)
		step();
}

void EightBit::mc6850::step() {

	if (!(powered() && selected()))
		return;

	const bool writing = RW() == PinLevel::Low;
	const bool reading = !writing;

	const bool registers = RS() == PinLevel::Low;
	const bool transferring = !registers;

	if (registers) {
		if (writing) {
			// Control register
			m_counterDivide = DATA() && (CR0 | CR1);
			const bool masterReset = m_counterDivide == 0b11;
			if (masterReset) {
				reset();
			} else {
				m_wordConfiguration = (DATA() && (CR2 | CR3 | CR4)) >> 2;
				m_transmitterControl = (DATA() && (CR5 | CR6)) >> 5;
				m_receiveControl = (DATA() && CR7) >> 7;
			}
		} else {
			// Status register
			assert(reading);
			DATA() = status();
		}
	} else {
		assert(transferring);
		IRQ() = PinLevel::High;
		if (writing) {
			fillTDR(DATA());
		} else {
			assert(reading);
			DATA() = drainRDR();
		}
	}
}

void EightBit::mc6850::fillRDR(uint8_t data) {
	RDR() = data;
	Processor::setFlag(status(), RDRF, true);
}

uint8_t EightBit::mc6850::drainRDR() {
	Processor::setFlag(status(), RDRF, false);
	return RDR();
}

void EightBit::mc6850::fillTDR(uint8_t data) {
	TDR() = data;
}

uint8_t EightBit::mc6850::drainTDR() {
	return TDR();
}