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281 lines
7.2 KiB
C++
281 lines
7.2 KiB
C++
//
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// 6526Implementation.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 18/07/2021.
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// Copyright © 2021 Thomas Harte. All rights reserved.
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//
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#ifndef _526Implementation_h
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#define _526Implementation_h
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#include <cassert>
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#include <cstdio>
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namespace MOS {
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namespace MOS6526 {
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template <typename BusHandlerT, Personality personality>
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template <int port> void MOS6526<BusHandlerT, personality>::set_port_output() {
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const uint8_t output = output_[port] | (~data_direction_[port]);
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port_handler_.set_port_output(Port(port), output);
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}
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template <typename BusHandlerT, Personality personality>
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template <int port> uint8_t MOS6526<BusHandlerT, personality>::get_port_input() {
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const uint8_t input = port_handler_.get_port_input(Port(port));
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return (input & ~data_direction_[port]) | (output_[port] & data_direction_[port]);
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}
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template <typename BusHandlerT, Personality personality>
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void MOS6526<BusHandlerT, personality>::posit_interrupt(uint8_t mask) {
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if(!mask) {
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return;
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}
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interrupt_state_ |= mask;
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update_interrupts();
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}
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template <typename BusHandlerT, Personality personality>
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void MOS6526<BusHandlerT, personality>::update_interrupts() {
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if(interrupt_state_ & interrupt_control_) {
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pending_ |= InterruptInOne;
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}
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}
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template <typename BusHandlerT, Personality personality>
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bool MOS6526<BusHandlerT, personality>::get_interrupt_line() {
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return interrupt_state_ & 0x80;
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}
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template <typename BusHandlerT, Personality personality>
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void MOS6526<BusHandlerT, personality>::write(int address, uint8_t value) {
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address &= 0xf;
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switch(address) {
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// Port output.
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case 0:
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output_[0] = value;
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set_port_output<0>();
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break;
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case 1:
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output_[1] = value;
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set_port_output<1>();
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break;
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// Port direction.
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case 2:
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data_direction_[0] = value;
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set_port_output<0>();
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break;
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case 3:
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data_direction_[1] = value;
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set_port_output<1>();
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break;
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// Counters; writes set the reload values.
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case 4: counter_[0].template set_reload<0>(value); break;
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case 5: counter_[0].template set_reload<8>(value); break;
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case 6: counter_[1].template set_reload<0>(value); break;
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case 7: counter_[1].template set_reload<8>(value); break;
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// Time-of-day clock.
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//
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// 8520: a binary counter; stopped on any write, restarted
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// upon a write to the LSB.
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case 8:
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if constexpr (personality == Personality::P8250) {
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if(counter_[1].control & 0x80) {
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tod_alarm_ = (tod_alarm_ & 0xffff00) | uint32_t(value);
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} else {
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tod_ = (tod_ & 0xffff00) | uint32_t(value);
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tod_increment_mask_ = uint32_t(~0);
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}
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} else {
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printf("6526 TOD clock not implemented\n");
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assert(false);
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}
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break;
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case 9:
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if constexpr (personality == Personality::P8250) {
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if(counter_[1].control & 0x80) {
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tod_alarm_ = (tod_alarm_ & 0xff00ff) | uint32_t(value << 8);
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} else {
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tod_ = (tod_ & 0xff00ff) | uint32_t(value << 8);
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tod_increment_mask_ = 0;
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}
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} else {
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printf("6526 TOD clock not implemented\n");
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assert(false);
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}
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break;
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case 10:
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if constexpr (personality == Personality::P8250) {
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if(counter_[1].control & 0x80) {
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tod_alarm_ = (tod_alarm_ & 0x00ffff) | uint32_t(value << 16);
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} else {
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tod_ = (tod_ & 0x00ffff) | uint32_t(value << 16);
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tod_increment_mask_ = 0;
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}
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} else {
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printf("6526 TOD clock not implemented\n");
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assert(false);
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}
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break;
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case 11:
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if constexpr (personality != Personality::P8250) {
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printf("6526 TOD clock not implemented\n");
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assert(false);
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}
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break;
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// Interrupt control.
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case 13: {
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if(value & 0x80) {
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interrupt_control_ |= value & 0x7f;
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} else {
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interrupt_control_ &= ~(value & 0x7f);
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}
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update_interrupts();
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} break;
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// Control.
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case 14: counter_[0].template set_control<false>(value); break;
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case 15: counter_[1].template set_control<true>(value); break;
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default:
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printf("Unhandled 6526 write: %02x to %d\n", value, address);
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assert(false);
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break;
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}
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}
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template <typename BusHandlerT, Personality personality>
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uint8_t MOS6526<BusHandlerT, personality>::read(int address) {
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address &= 0xf;
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switch(address) {
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case 0: return get_port_input<0>();
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case 1: return get_port_input<1>();
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case 2: case 3:
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return data_direction_[address - 2];
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// Counters; reads obtain the current values.
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case 4: return uint8_t(counter_[0].value >> 0);
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case 5: return uint8_t(counter_[0].value >> 8);
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case 6: return uint8_t(counter_[1].value >> 0);
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case 7: return uint8_t(counter_[1].value >> 8);
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// Interrupt state.
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case 13: {
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const uint8_t result = interrupt_state_;
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interrupt_state_ = 0;
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pending_ &= ~(InterruptNow | InterruptInOne);
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update_interrupts();
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return result;
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} break;
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case 14: case 15:
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return counter_[address - 14].control;
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// Time-of-day clock.
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//
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// 8250: Latch on MSB. Unlatch on LSB. Read raw if not latched.
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case 8:
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if constexpr (personality == Personality::P8250) {
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if(tod_latch_) {
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const uint8_t result = tod_latch_ & 0xff;
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tod_latch_ = 0;
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return result;
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} else {
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return tod_ & 0xff;
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}
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} else {
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printf("6526 TOD clock not implemented\n");
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assert(false);
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}
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break;
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case 9:
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if constexpr (personality == Personality::P8250) {
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if(tod_latch_) {
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return (tod_latch_ >> 8) & 0xff;
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} else {
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return (tod_ >> 8) & 0xff;
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}
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} else {
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printf("6526 TOD clock not implemented\n");
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assert(false);
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}
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break;
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case 10:
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if constexpr (personality == Personality::P8250) {
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tod_latch_ = tod_ | 0xff00'0000;
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return (tod_ >> 16) & 0xff;
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} else {
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printf("6526 TOD clock not implemented\n");
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assert(false);
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}
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break;
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case 11:
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if constexpr (personality == Personality::P8250) {
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return 0x00; // Assumed. Just a guss.
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} else {
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printf("6526 TOD clock not implemented\n");
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assert(false);
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}
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break;
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default:
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printf("Unhandled 6526 read from %d\n", address);
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assert(false);
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break;
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}
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return 0xff;
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}
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template <typename BusHandlerT, Personality personality>
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void MOS6526<BusHandlerT, personality>::run_for(const HalfCycles half_cycles) {
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half_divider_ += half_cycles;
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int sub = half_divider_.divide_cycles().template as<int>();
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while(sub--) {
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pending_ <<= 1;
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if(pending_ & InterruptNow) {
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interrupt_state_ |= 0x80;
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}
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pending_ &= PendingClearMask;
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// TODO: use CNT potentially to clock timer A, elimiante conditional above.
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const bool timer1_did_reload = counter_[0].advance(false);
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const bool timer1_carry = timer1_did_reload && (counter_[1].control & 0x60) == 0x40;
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const bool timer2_did_reload = counter_[1].advance(timer1_carry);
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posit_interrupt((timer1_did_reload ? 0x01 : 0x00) | (timer2_did_reload ? 0x02 : 0x00));
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}
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}
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template <typename BusHandlerT, Personality personality>
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void MOS6526<BusHandlerT, personality>::advance_tod(int count) {
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if(!count) return;
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if constexpr(personality == Personality::P8250) {
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// The 8250 uses a simple binary counter to replace the
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// 6526's time-of-day clock. So this is easy.
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const uint32_t distance_to_alarm_ = (tod_alarm_ - tod_) & 0xffffff;
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tod_ += uint32_t(count) & tod_increment_mask_;
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if(distance_to_alarm_ <= uint32_t(count)) {
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posit_interrupt(0x04);
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}
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} else {
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// The 6526 uses a time-of-day clock. This may or may not
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// be accurate.
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}
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}
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}
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}
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#endif /* _526Implementation_h */
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