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154 lines
3.0 KiB
C++
154 lines
3.0 KiB
C++
//
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// PIC.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 21/11/2023.
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// Copyright © 2023 Thomas Harte. All rights reserved.
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//
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#ifndef PIC_hpp
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#define PIC_hpp
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namespace PCCompatible {
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// Cf. https://helppc.netcore2k.net/hardware/pic
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class PIC {
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public:
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template <int address>
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void write(uint8_t value) {
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if(address) {
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if(config_.word >= 0) {
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switch(config_.word) {
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case 0:
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vector_base_ = value;
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break;
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case 1:
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if(config_.has_fourth_word) {
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// TODO:
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//
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// (1) slave mask if this is a master;
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// (2) master interrupt attachment if this is a slave.
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}
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[[fallthrough]];
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case 2:
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auto_eoi_ = value & 2;
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break;
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}
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++config_.word;
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if(config_.word == (config_.has_fourth_word ? 3 : 2)) {
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config_.word = -1;
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}
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} else {
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mask_ = value;
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}
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} else {
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if(value & 0x10) {
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//
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// Initialisation Command Word 1.
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//
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config_.word = 0;
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config_.has_fourth_word = value & 1;
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if(!config_.has_fourth_word) {
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auto_eoi_ = false;
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}
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single_pic_ = value & 2;
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four_byte_vectors_ = value & 4;
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level_triggered_ = value & 8;
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} else if(value & 0x08) {
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//
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// Operation Control Word 3.
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//
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// b6: 1 => use b5; 0 => ignore.
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// b5: 1 => set special mask; 0 => clear.
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// b2: 1 => poll command issued; 0 => not.
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// b1: 1 => use b0; 0 => ignore.
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// b0: 1 => read IRR on next read; 0 => read ISR.
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} else {
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//
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// Operation Control Word 2.
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//
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// b7, b6, b5: EOI type.
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// b2, b1, b0: interrupt level to acknowledge.
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if((value >> 5) == 0b001) {
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// Non-specific EOI.
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awaiting_eoi_ = false;
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}
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}
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}
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}
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template <int address>
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uint8_t read() {
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if(address) {
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return mask_;
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}
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return 0;
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}
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template <int input>
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void apply_edge(bool final_level) {
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const uint8_t input_mask = 1 << input;
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// Guess: level triggered means the request can be forwarded only so long as the
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// relevant input is actually high. Whereas edge triggered implies capturing state.
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if(level_triggered_) {
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requests_ &= ~input_mask;
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}
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if(final_level) {
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requests_ |= input_mask;
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}
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}
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bool pending() {
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// Per the OSDev Wiki, masking is applied after the fact.
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return !awaiting_eoi_ && (requests_ & ~mask_);
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}
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int acknowledge() {
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awaiting_eoi_ = true;
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in_service_ = 0x01;
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int id = 0;
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while(!(in_service_ & requests_) && in_service_) {
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in_service_ <<= 1;
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++id;
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}
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if(in_service_) {
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requests_ &= ~in_service_;
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return vector_base_ + id;
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}
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// Spurious interrupt.
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return vector_base_ + 7;
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}
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private:
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bool single_pic_ = false;
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bool four_byte_vectors_ = false;
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bool level_triggered_ = false;
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bool auto_eoi_ = false;
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uint8_t vector_base_ = 0;
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uint8_t mask_ = 0;
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bool awaiting_eoi_ = false;
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uint8_t requests_ = 0;
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uint8_t in_service_ = 0;
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struct ConfgurationState {
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int word;
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bool has_fourth_word;
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} config_;
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};
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}
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#endif /* PIC_hpp */
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