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90 lines
1.6 KiB
C++
90 lines
1.6 KiB
C++
//
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// 6526Storage.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 _526Storage_h
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#define _526Storage_h
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namespace MOS {
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namespace MOS6526 {
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struct MOS6526Storage {
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HalfCycles half_divider_;
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uint8_t output_[2] = {0, 0};
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uint8_t data_direction_[2] = {0, 0};
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uint8_t interrupt_control_ = 0;
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uint8_t interrupt_state_ = 0;
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uint32_t tod_increment_mask_ = uint32_t(~0);
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uint32_t tod_latch_ = 0;
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uint32_t tod_ = 0;
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uint32_t tod_alarm_ = 0;
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struct Counter {
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uint16_t reload = 0;
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uint16_t value = 0;
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uint8_t control = 0;
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template <int shift> void set_reload(uint8_t v) {
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reload = (reload & (0xff00 >> shift)) | uint16_t(v << shift);
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if constexpr (shift == 8) {
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if(!(control&1)) {
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value = reload;
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if(control&8) {
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control |= 1; // At a guess: start one-shot automatically (?)
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}
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}
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}
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}
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template <bool is_counter_2> void set_control(uint8_t v) {
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control = v & 0xef;
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if(v & 0x10) {
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value = reload;
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}
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// Force reload + one-shot => start counting (?)
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if((v & 0x18) == 0x18) {
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control |= 1;
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}
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}
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int subtract(int count) {
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if(control & 8) {
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// One-shot.
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if(value < count) {
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value = reload;
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control &= 0xfe;
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return 1;
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} else {
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value -= count;
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}
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return 0;
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} else {
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// Continuous.
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value -= count;
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value -= (reload + 1);
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const int underflows = -value / (reload + 1);
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value %= (reload + 1);
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value += (reload + 1);
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return underflows;
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}
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}
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} counter_[2];
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};
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}
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}
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#endif /* _526Storage_h */
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