5150/arduino/kbd/kbd.cc

// keyboard wiring diagram:
// https://www.minuszerodegrees.net/5150/misc/5150_keyboard_reset.jpg

#include "Arduino.h"

constexpr int kClockPin = PC6;
constexpr int kDataPin = PC4;

constexpr int kBitDelayMicros = 100;
constexpr int kCodeDelayMicros = 200;
constexpr int kKeyDelayMicros = 100;

namespace {

void sendCode(int code) {
    // preconditions: clock and data pins are INPUT

    while (digitalRead(kDataPin) == LOW || digitalRead(kClockPin) == LOW) {
        // wait. we're not allowed to send
    }

    digitalWrite(kDataPin, LOW);
    digitalWrite(kClockPin, LOW);

    pinMode(kClockPin, OUTPUT);
    delayMicroseconds(kBitDelayMicros);
    pinMode(kClockPin, INPUT);
    // delayMicroseconds(kDelayMicros);

    for (int i = 0; i < 8; i++) {
        if ((code & (1 << i)) == 0) {
            // send a 0
            pinMode(kDataPin, OUTPUT);
        } // else do nothing, it's already a 1
        delayMicroseconds(kBitDelayMicros);

        pinMode(kClockPin, OUTPUT);
        delayMicroseconds(kBitDelayMicros);
        pinMode(kDataPin, INPUT);
        pinMode(kClockPin, INPUT);
    }
    delayMicroseconds(kCodeDelayMicros);
}

enum State {
    kReady,
    kMaybeReset,
};

constexpr int kResetDelay = 19;

constexpr int kLetterCodes[] = {
        0x1E, // 'a'
        0x30, 0x2E, 0x20, 0x12, 0x21, 0x22, 0x23, 0x17, 0x24,
        0x25, 0x26, 0x32, 0x31, 0x18, 0x19, 0x10, 0x13, 0x1F,
        0x14, 0x16, 0x2F, 0x11, 0x2D, 0x15, 0x2c,
};

constexpr int kNumberCodes[] = {
        0x0B, // '0'
        0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A,
};

void sendNormalCode(int code) {
    sendCode(code);
    sendCode(code | 0x80);
}

void sendShiftCode(int code) {
    sendCode(42); // left shift
    sendNormalCode(code);
    sendCode(42 | 0x80);
}

void sendCtrlAltDel() {
    sendCode(0x1d); // ctrl
    sendCode(0x38); // alt
    sendCode(0x53); // del
    sendCode(0x53 | 0x80);
    sendCode(0x38 | 0x80);
    sendCode(0x1d | 0x80);
}

void sendCtrlBreak() {
    sendCode(0x1d); // ctrl
    sendCode(0x46); // break
    sendCode(0x46 | 0x80);
    sendCode(0x1d | 0x80);
}

} // namespace

void sendAsciiChar(int c) {
    if (c >= 'a' && c <= 'z') {
        return sendNormalCode(kLetterCodes[c - 'a']);
    } else if (c >= '0' && c <= '9') {
        return sendNormalCode(kNumberCodes[c - '0']);
    } else if (c >= 'A' && c <= 'Z') {
        return sendShiftCode(kLetterCodes[c - 'A']);
    }
    switch (c) {
    case '-':
        return sendNormalCode(12);
    case '=':
        return sendNormalCode(13);
    case '[':
        return sendNormalCode(26);
    case ']':
        return sendNormalCode(27);
    case ';':
        return sendNormalCode(39);
    case '\'':
        return sendNormalCode(40);
    case ',':
        return sendNormalCode(51);
    case '.':
        return sendNormalCode(52);
    case '/':
        return sendNormalCode(53);
    case ' ':
        return sendNormalCode(57);
    case '\n':
        return sendNormalCode(28);

    case '!':
        return sendShiftCode(2);
    case '@':
        return sendShiftCode(3);
    case '#':
        return sendShiftCode(4);
    case '$':
        return sendShiftCode(5);
    case '%':
        return sendShiftCode(6);
    case '^':
        return sendShiftCode(7);
    case '&':
        return sendShiftCode(8);
    case '*':
        return sendShiftCode(9);
    case '(':
        return sendShiftCode(10);
    case ')':
        return sendShiftCode(11);
    case '_':
        return sendShiftCode(12);
    case '+':
        return sendShiftCode(13);

    case '{':
        return sendShiftCode(26);
    case '}':
        return sendShiftCode(27);
    case ':':
        return sendShiftCode(39);
    case '"':
        return sendShiftCode(40);
    case '<':
        return sendShiftCode(51);
    case '>':
        return sendShiftCode(52);
    case '?':
        return sendShiftCode(53);

    case 0:
        return sendCtrlAltDel();
    case 27:
        return sendCtrlBreak(); // escape
    }
}

void setupKbd() {
    pinMode(kClockPin, INPUT);
    pinMode(kDataPin, INPUT);
}

void checkKbdReset() {
    static State state = kReady;
    static int lastclocklow = 0;

    int clockp = digitalRead(kClockPin);
    if (state == State::kReady && clockp == LOW) {
        state = State::kMaybeReset;
        lastclocklow = millis();
    } else if (state == State::kMaybeReset) {
        if (clockp == HIGH && millis() - lastclocklow > kResetDelay) {
            delay(1);
            state = State::kReady;
            sendCode(0xaa);
            Serial.println("Reset!");
        }
    }
}