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375 lines
13 KiB
C++
375 lines
13 KiB
C++
//
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// MFP68901.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 06/10/2019.
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// Copyright © 2019 Thomas Harte. All rights reserved.
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//
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#include "MFP68901.hpp"
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#include <algorithm>
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#include <cstring>
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#ifndef NDEBUG
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#define NDEBUG
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#endif
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#define LOG_PREFIX "[MFP] "
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#include "../../Outputs/Log.hpp"
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using namespace Motorola::MFP68901;
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ClockingHint::Preference MFP68901::preferred_clocking() const {
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// Rule applied: if any timer is actively running and permitted to produce an
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// interrupt, request real-time running.
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return
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(timers_[0].mode >= TimerMode::Delay && interrupt_enable_&Interrupt::TimerA) ||
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(timers_[1].mode >= TimerMode::Delay && interrupt_enable_&Interrupt::TimerB) ||
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(timers_[2].mode >= TimerMode::Delay && interrupt_enable_&Interrupt::TimerC) ||
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(timers_[3].mode >= TimerMode::Delay && interrupt_enable_&Interrupt::TimerD)
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? ClockingHint::Preference::RealTime : ClockingHint::Preference::JustInTime;
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}
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uint8_t MFP68901::read(int address) {
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address &= 0x1f;
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// Interrupt block: various bits of state can be read, all passively.
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if(address >= 0x03 && address <= 0x0b) {
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const int shift = (address&1) << 3;
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switch(address) {
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case 0x03: case 0x04: return uint8_t(interrupt_enable_ >> shift);
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case 0x05: case 0x06: return uint8_t(interrupt_pending_ >> shift);
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case 0x07: case 0x08: return uint8_t(interrupt_in_service_ >> shift);
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case 0x09: case 0x0a: return uint8_t(interrupt_mask_ >> shift);
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case 0x0b: return interrupt_vector_;
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default: break;
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}
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}
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switch(address) {
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// GPIP block: input, and configured active edge and direction values.
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case 0x00: return (gpip_input_ & ~gpip_direction_) | (gpip_output_ & gpip_direction_);
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case 0x01: return gpip_active_edge_;
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case 0x02: return gpip_direction_;
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/* Interrupt block dealt with above. */
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default: break;
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// Timer block: read back A, B and C/D control, and read current timer values.
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case 0x0c: case 0x0d: return timer_ab_control_[address - 0xc];
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case 0x0e: return timer_cd_control_;
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case 0x0f: case 0x10:
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case 0x11: case 0x12: return get_timer_data(address - 0xf);
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// USART block: TODO.
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case 0x13: LOG("Read: sync character generator"); break;
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case 0x14: LOG("Read: USART control"); break;
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case 0x15: LOG("Read: receiver status"); break;
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case 0x16: LOG("Read: transmitter status"); break;
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case 0x17: LOG("Read: USART data"); break;
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}
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return 0x00;
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}
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void MFP68901::write(int address, uint8_t value) {
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address &= 0x1f;
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// Interrupt block: enabled and masked interrupts can be set; pending and in-service interrupts can be masked.
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if(address >= 0x03 && address <= 0x0b) {
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const int shift = (address&1) << 3;
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const int preserve = 0xff00 >> shift;
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const int word_value = value << shift;
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switch(address) {
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default: break;
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case 0x03: case 0x04: // Adjust enabled interrupts; disabled ones also cease to be pending.
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interrupt_enable_ = (interrupt_enable_ & preserve) | word_value;
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interrupt_pending_ &= interrupt_enable_;
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break;
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case 0x05: case 0x06: // Resolve pending interrupts.
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interrupt_pending_ &= (preserve | word_value);
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break;
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case 0x07: case 0x08: // Resolve in-service interrupts.
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interrupt_in_service_ &= (preserve | word_value);
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break;
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case 0x09: case 0x0a: // Adjust interrupt mask.
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interrupt_mask_ = (interrupt_mask_ & preserve) | word_value;
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break;
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case 0x0b: // Set the interrupt vector, possibly changing end-of-interrupt mode.
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interrupt_vector_ = value;
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// If automatic end-of-interrupt mode has now been enabled, clear
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// the in-process mask and re-evaluate.
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if(interrupt_vector_ & 0x08) return;
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interrupt_in_service_ = 0;
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break;
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}
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// Whatever just happened may have affected the state of the interrupt line.
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update_interrupts();
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update_clocking_observer();
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return;
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}
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constexpr int timer_prescales[] = {
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1, 4, 10, 16, 50, 64, 100, 200
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};
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switch(address) {
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// GPIP block: output and configuration of active edge and direction values.
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case 0x00:
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gpip_output_ = value;
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break;
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case 0x01:
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gpip_active_edge_ = value;
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reevaluate_gpip_interrupts();
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break;
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case 0x02:
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gpip_direction_ = value;
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reevaluate_gpip_interrupts();
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break;
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/* Interrupt block dealt with above. */
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default: break;
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// Timer block.
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case 0x0c:
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case 0x0d: {
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const auto timer = address - 0xc;
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const bool reset = value & 0x10;
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timer_ab_control_[timer] = value;
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switch(value & 0xf) {
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case 0x0: set_timer_mode(timer, TimerMode::Stopped, 1, reset); break;
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case 0x1: set_timer_mode(timer, TimerMode::Delay, 4, reset); break;
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case 0x2: set_timer_mode(timer, TimerMode::Delay, 10, reset); break;
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case 0x3: set_timer_mode(timer, TimerMode::Delay, 16, reset); break;
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case 0x4: set_timer_mode(timer, TimerMode::Delay, 50, reset); break;
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case 0x5: set_timer_mode(timer, TimerMode::Delay, 64, reset); break;
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case 0x6: set_timer_mode(timer, TimerMode::Delay, 100, reset); break;
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case 0x7: set_timer_mode(timer, TimerMode::Delay, 200, reset); break;
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case 0x8: set_timer_mode(timer, TimerMode::EventCount, 1, reset); break;
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case 0x9: set_timer_mode(timer, TimerMode::PulseWidth, 4, reset); break;
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case 0xa: set_timer_mode(timer, TimerMode::PulseWidth, 10, reset); break;
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case 0xb: set_timer_mode(timer, TimerMode::PulseWidth, 16, reset); break;
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case 0xc: set_timer_mode(timer, TimerMode::PulseWidth, 50, reset); break;
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case 0xd: set_timer_mode(timer, TimerMode::PulseWidth, 64, reset); break;
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case 0xe: set_timer_mode(timer, TimerMode::PulseWidth, 100, reset); break;
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case 0xf: set_timer_mode(timer, TimerMode::PulseWidth, 200, reset); break;
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}
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} break;
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case 0x0e:
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timer_cd_control_ = value;
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set_timer_mode(3, (value & 7) ? TimerMode::Delay : TimerMode::Stopped, timer_prescales[value & 7], false);
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set_timer_mode(2, ((value >> 4) & 7) ? TimerMode::Delay : TimerMode::Stopped, timer_prescales[(value >> 4) & 7], false);
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break;
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case 0x0f: case 0x10: case 0x11: case 0x12:
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set_timer_data(address - 0xf, value);
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break;
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// USART block: TODO.
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case 0x13: LOG("Write: sync character generator"); break;
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case 0x14: LOG("Write: USART control"); break;
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case 0x15: LOG("Write: receiver status"); break;
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case 0x16: LOG("Write: transmitter status"); break;
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case 0x17: LOG("Write: USART data"); break;
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}
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update_clocking_observer();
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}
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void MFP68901::run_for(HalfCycles time) {
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cycles_left_ += time;
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const int cycles = int(cycles_left_.flush<Cycles>().as_integral());
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if(!cycles) return;
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for(int c = 0; c < 4; ++c) {
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if(timers_[c].mode >= TimerMode::Delay) {
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// This code applies the timer prescaling only. prescale_count is used to count
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// upwards rather than downwards for simplicity, but on the real hardware it's
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// pretty safe to assume it actually counted downwards. So the clamp to 0 is
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// because gymnastics may need to occur when the prescale value is altered, e.g.
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// if a prescale of 256 is set and the prescale_count is currently 2 then the
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// counter should roll over in 254 cycles. If the user at that point changes the
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// prescale_count to 1 then the counter will need to be altered to -253 and
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// allowed to keep counting up until it crosses both 0 and 1.
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const int dividend = timers_[c].prescale_count + cycles;
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const int decrements = std::max(dividend / timers_[c].prescale, 0);
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if(decrements) {
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decrement_timer(c, decrements);
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timers_[c].prescale_count = dividend % timers_[c].prescale;
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} else {
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timers_[c].prescale_count += cycles;
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}
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}
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}
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}
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HalfCycles MFP68901::get_next_sequence_point() {
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return HalfCycles::max();
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}
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// MARK: - Timers
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void MFP68901::set_timer_mode(int timer, TimerMode mode, int prescale, bool reset_timer) {
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LOG("Timer " << timer << " mode set: " << int(mode) << "; prescale: " << prescale);
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timers_[timer].mode = mode;
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if(reset_timer) {
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timers_[timer].prescale_count = 0;
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timers_[timer].value = timers_[timer].reload_value;
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} else {
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// This hoop is because the prescale_count here goes upward but I'm assuming it goes downward in
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// real hardware. Therefore this deals with the "switched to a lower prescaling" case whereby the
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// old cycle should be allowed naturally to expire.
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timers_[timer].prescale_count = prescale - (timers_[timer].prescale - timers_[timer].prescale_count);
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}
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timers_[timer].prescale = prescale;
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}
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void MFP68901::set_timer_data(int timer, uint8_t value) {
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if(timers_[timer].mode == TimerMode::Stopped) {
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timers_[timer].value = value;
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}
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timers_[timer].reload_value = value;
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}
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uint8_t MFP68901::get_timer_data(int timer) {
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return timers_[timer].value;
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}
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void MFP68901::set_timer_event_input(int channel, bool value) {
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if(timers_[channel].event_input == value) return;
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timers_[channel].event_input = value;
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if(timers_[channel].mode == TimerMode::EventCount && (value == !!(gpip_active_edge_ & (0x10 >> channel)))) {
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// "The active state of the signal on TAI or TBI is dependent upon the associated
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// Interrupt Channel’s edge bit (GPIP 4 for TAI and GPIP 3 for TBI [...] ).
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// If the edge bit associated with the TAI or TBI input is a one, it will be active high.
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decrement_timer(channel, 1);
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}
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// TODO:
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//
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// Altering the edge bit while the timer is in the event count mode can produce a count pulse.
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// The interrupt channel associated with the input (I3 for I4 for TAI) is allowed to function normally.
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// To count transitions reliably, the input must remain in each state (1/O) for a length of time equal
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// to four periods of the timer clock.
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//
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// (the final bit probably explains 13 cycles of the DE to interrupt latency; not sure about the other ~15)
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}
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void MFP68901::decrement_timer(int timer, int amount) {
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while(amount--) {
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--timers_[timer].value;
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if(timers_[timer].value < 1) {
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switch(timer) {
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case 0: begin_interrupts(Interrupt::TimerA); break;
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case 1: begin_interrupts(Interrupt::TimerB); break;
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case 2: begin_interrupts(Interrupt::TimerC); break;
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case 3: begin_interrupts(Interrupt::TimerD); break;
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}
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// Re: reloading when in event counting mode; I found the data sheet thoroughly unclear on
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// this, but it appears empirically to be correct. See e.g. Pompey Pirates menu 27.
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if(timers_[timer].mode == TimerMode::Delay || timers_[timer].mode == TimerMode::EventCount) {
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timers_[timer].value += timers_[timer].reload_value; // TODO: properly.
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}
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}
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}
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}
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// MARK: - GPIP
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void MFP68901::set_port_input(uint8_t input) {
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gpip_input_ = input;
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reevaluate_gpip_interrupts();
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}
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uint8_t MFP68901::get_port_output() {
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return 0xff; // TODO.
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}
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void MFP68901::reevaluate_gpip_interrupts() {
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const uint8_t gpip_state = (gpip_input_ & ~gpip_direction_) ^ gpip_active_edge_;
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// An interrupt is detected on any falling edge.
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const uint8_t new_interrupt_mask = (gpip_state ^ gpip_interrupt_state_) & gpip_interrupt_state_;
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if(new_interrupt_mask) {
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begin_interrupts(
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(new_interrupt_mask & 0x0f) |
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((new_interrupt_mask & 0x30) << 2) |
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((new_interrupt_mask & 0xc0) << 8)
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);
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}
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gpip_interrupt_state_ = gpip_state;
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}
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// MARK: - Interrupts
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void MFP68901::begin_interrupts(int interrupt) {
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interrupt_pending_ |= interrupt & interrupt_enable_;
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update_interrupts();
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}
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void MFP68901::end_interrupts(int interrupt) {
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interrupt_pending_ &= ~interrupt;
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update_interrupts();
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}
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void MFP68901::update_interrupts() {
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const auto old_interrupt_line = interrupt_line_;
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const auto firing_interrupts = interrupt_pending_ & interrupt_mask_;
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if(!firing_interrupts) {
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interrupt_line_ = false;
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} else {
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if(interrupt_vector_ & 0x8) {
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// Software interrupt mode: permit only if neither this interrupt
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// nor a higher interrupt is currently in service.
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const int highest_bit = msb16(firing_interrupts);
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interrupt_line_ = !(interrupt_in_service_ & ~(highest_bit + highest_bit - 1));
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} else {
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// Auto-interrupt mode; just signal.
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interrupt_line_ = true;
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}
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}
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// Update the delegate if necessary.
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if(interrupt_delegate_ && interrupt_line_ != old_interrupt_line) {
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interrupt_delegate_->mfp68901_did_change_interrupt_status(this);
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}
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}
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bool MFP68901::get_interrupt_line() {
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return interrupt_line_;
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}
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int MFP68901::acknowledge_interrupt() {
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if(!(interrupt_pending_ & interrupt_mask_)) {
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return NoAcknowledgement;
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}
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const int mask = msb16(interrupt_pending_ & interrupt_mask_);
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// Clear the pending bit regardless.
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interrupt_pending_ &= ~mask;
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// If this is software interrupt mode, set the in-service bit.
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if(interrupt_vector_ & 0x8) {
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interrupt_in_service_ |= mask;
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}
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update_interrupts();
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int selected = 0;
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while((1 << selected) != mask) ++selected;
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// LOG("Interrupt acknowledged: " << selected);
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return (interrupt_vector_ & 0xf0) | uint8_t(selected);
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}
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void MFP68901::set_interrupt_delegate(InterruptDelegate *delegate) {
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interrupt_delegate_ = delegate;
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}
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