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95 lines
2.4 KiB
C++
95 lines
2.4 KiB
C++
//
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// i8255.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 01/08/2017.
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// Copyright 2017 Thomas Harte. All rights reserved.
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//
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#ifndef i8255_hpp
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#define i8255_hpp
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#include <cstdint>
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namespace Intel {
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namespace i8255 {
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class PortHandler {
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public:
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void set_value([[maybe_unused]] int port, [[maybe_unused]] uint8_t value) {}
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uint8_t get_value([[maybe_unused]] int port) { return 0xff; }
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};
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// TODO: Modes 1 and 2.
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template <class T> class i8255 {
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public:
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i8255(T &port_handler) : control_(0), outputs_{0, 0, 0}, port_handler_(port_handler) {}
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/*!
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Stores the value @c value to the register at @c address. If this causes a change in 8255 output
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then the PortHandler will be informed.
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*/
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void write(int address, uint8_t value) {
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switch(address & 3) {
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case 0:
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if(!(control_ & 0x10)) {
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// TODO: so what would output be when switching from input to output mode?
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outputs_[0] = value; port_handler_.set_value(0, value);
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}
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break;
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case 1:
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if(!(control_ & 0x02)) {
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outputs_[1] = value; port_handler_.set_value(1, value);
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}
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break;
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case 2: outputs_[2] = value; port_handler_.set_value(2, value); break;
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case 3:
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if(value & 0x80) {
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control_ = value;
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} else {
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if(value & 1) {
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outputs_[2] |= 1 << ((value >> 1)&7);
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} else {
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outputs_[2] &= ~(1 << ((value >> 1)&7));
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}
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}
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update_outputs();
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break;
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}
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}
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/*!
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Obtains the current value for the register at @c address. If this provides a reading
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of input then the PortHandler will be queried.
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*/
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uint8_t read(int address) {
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switch(address & 3) {
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case 0: return (control_ & 0x10) ? port_handler_.get_value(0) : outputs_[0];
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case 1: return (control_ & 0x02) ? port_handler_.get_value(1) : outputs_[1];
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case 2: {
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if(!(control_ & 0x09)) return outputs_[2];
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uint8_t input = port_handler_.get_value(2);
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return ((control_ & 0x01) ? (input & 0x0f) : (outputs_[2] & 0x0f)) | ((control_ & 0x08) ? (input & 0xf0) : (outputs_[2] & 0xf0));
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}
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case 3: return control_;
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}
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return 0xff;
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}
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private:
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void update_outputs() {
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if(!(control_ & 0x10)) port_handler_.set_value(0, outputs_[0]);
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if(!(control_ & 0x02)) port_handler_.set_value(1, outputs_[1]);
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port_handler_.set_value(2, outputs_[2]);
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}
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uint8_t control_;
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uint8_t outputs_[3];
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T &port_handler_;
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};
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}
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}
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#endif /* i8255_hpp */
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