io/model.cpp


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#include <array>
#include <cstdint>
#include <iostream>
#include <utility>

#include "io/model.h"
#include "isa/isa.h"

bool iomodel::interact(std::array<unsigned int, NUM_CTLREGS> &ctlregs) {
    auto [ebegin, eend] = log.equal_range(time);
    for (auto e = ebegin; e != eend; ++e) {
        auto &r = ctlregs[e->second.reg];
        r &= ~e->second.mask;
        r |= e->second.value;
    }

    ++time;

    if (ctlregs[TT_OUTPUT] & 0x100) {
        // PDP-8 doesn't really have support for 8-bit output, this is Jules' contribution
        std::cout << (char)((ctlregs[TT_OUTPUT] & 0xff) ^ 0x80) << std::flush;
        ctlregs[TT_OUTPUT] &= ~0x1ff;
        log.emplace(time + TT_OUTPUT_DELAY, event(TT_OUTPUT, 0x200, 0));
    }

    bool interrupt = false;
    if (ctlregs[INT_ENABLE] & 1) {
        if (ctlregs[TT_INPUT_INT_ENABLE]) {
            if (ctlregs[TT_INPUT] & 0x100)
                interrupt = true;
        }
        if (ctlregs[TT_OUTPUT_INT_ENABLE]) {
            if (!(ctlregs[TT_OUTPUT] & 0x400) && (ctlregs[TT_OUTPUT] & 0x200))
                interrupt = true;
        }
    }

    if (interrupt) {
        ctlregs[DATA_INSTRUCTION_FIELD_SAVED] = ctlregs[DATA_INSTRUCTION_FIELD_BUFFER];
        ctlregs[DATA_INSTRUCTION_FIELD_BUFFER] = 0;
        ctlregs[HALTED] = 0;
        ctlregs[INT_ENABLE] = 0;
        ctlregs[TT_OUTPUT] = (ctlregs[TT_OUTPUT] & 0x200) * 3;
    } else {
        ctlregs[INT_ENABLE] = (ctlregs[INT_ENABLE] >> 1) * 3;
    }

    return interrupt;
};