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CLK/Components/6850/6850.hpp

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//
// 6850.hpp
// Clock Signal
//
// Created by Thomas Harte on 10/10/2019.
// Copyright © 2019 Thomas Harte. All rights reserved.
//
#ifndef Motorola_ACIA_6850_hpp
#define Motorola_ACIA_6850_hpp
#include <cstdint>
#include "../../ClockReceiver/ClockReceiver.hpp"
#include "../../ClockReceiver/ForceInline.hpp"
#include "../../ClockReceiver/ClockingHintSource.hpp"
#include "../Serial/Line.hpp"
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namespace Motorola {
namespace ACIA {
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class ACIA: public ClockingHint::Source, private Serial::Line::ReadDelegate {
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public:
static constexpr const HalfCycles SameAsTransmit = HalfCycles(0);
/*!
Constructs a new instance of ACIA which will receive a transmission clock at a rate of
@c transmit_clock_rate, and a receive clock at a rate of @c receive_clock_rate.
*/
ACIA(HalfCycles transmit_clock_rate, HalfCycles receive_clock_rate = SameAsTransmit);
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/*!
Reads from the ACIA.
Bit 0 of the address is used as the ACIA's register select line
so even addresses select control/status registers, odd addresses
select transmit/receive data registers.
*/
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uint8_t read(int address);
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/*!
Writes to the ACIA.
Bit 0 of the address is used as the ACIA's register select line
so even addresses select control/status registers, odd addresses
select transmit/receive data registers.
*/
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void write(int address, uint8_t value);
/*!
Advances @c transmission_cycles in time, which should be
counted relative to the @c transmit_clock_rate.
*/
forceinline void run_for(HalfCycles transmission_cycles) {
if(transmit.transmission_data_time_remaining() > HalfCycles(0)) {
const auto write_data_time_remaining = transmit.write_data_time_remaining();
// There's at most one further byte available to enqueue, so a single 'if'
// rather than a 'while' is correct here. It's the responsibilit of the caller
// to ensure run_for lengths are appropriate for longer sequences.
if(transmission_cycles >= write_data_time_remaining) {
if(next_transmission_ != NoValueMask) {
transmit.advance_writer(write_data_time_remaining);
consider_transmission();
transmit.advance_writer(transmission_cycles - write_data_time_remaining);
} else {
transmit.advance_writer(transmission_cycles);
update_clocking_observer();
update_interrupt_line();
}
} else {
transmit.advance_writer(transmission_cycles);
}
}
}
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bool get_interrupt_line() const;
void reset();
// Input lines.
Serial::Line receive;
Serial::Line clear_to_send;
Serial::Line data_carrier_detect;
// Output lines.
Serial::Line transmit;
Serial::Line request_to_send;
// ClockingHint::Source.
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ClockingHint::Preference preferred_clocking() const final;
struct InterruptDelegate {
virtual void acia6850_did_change_interrupt_status(ACIA *acia) = 0;
};
void set_interrupt_delegate(InterruptDelegate *delegate);
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private:
int divider_ = 1;
enum class Parity {
Even, Odd, None
} parity_ = Parity::None;
int data_bits_ = 7, stop_bits_ = 2;
static constexpr int NoValueMask = 0x100;
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int next_transmission_ = NoValueMask;
int received_data_ = NoValueMask;
int bits_received_ = 0;
int bits_incoming_ = 0;
bool overran_ = false;
void consider_transmission();
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int expected_bits();
uint8_t parity(uint8_t value);
bool receive_interrupt_enabled_ = false;
bool transmit_interrupt_enabled_ = false;
HalfCycles transmit_clock_rate_;
HalfCycles receive_clock_rate_;
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bool serial_line_did_produce_bit(Serial::Line *line, int bit) final;
bool interrupt_line_ = false;
void update_interrupt_line();
InterruptDelegate *interrupt_delegate_ = nullptr;
uint8_t get_status();
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};
}
}
#endif /* Motorola_ACIA_6850_hpp */