Add parallel port comms to arduino

arduino/kbd/parallel.cc

@@ -0,0 +1,95 @@
+#include "parallel.h"
+
+#include <stdint.h>
+
+#include "Arduino.h"
+
+namespace {
+
+constexpr int kParallelDataPins[] = {
+        D9, D8, D7, D6, D5, D4, D3, D2,
+};
+
+constexpr int kParallelBusyPin = D14;
+constexpr int kParallelAckPin = D15;
+constexpr int kParallelPaperoutPin = D12;
+constexpr int kParallelSelectPin = D11;
+
+constexpr int kParallelNibblePins[] = {
+        kParallelSelectPin,
+        kParallelPaperoutPin,
+        kParallelAckPin,
+        kParallelBusyPin,
+};
+
+constexpr bool kParallelNibbleInverted[] = {
+        false,
+        false,
+        false,
+        true,
+};
+
+constexpr int kParallelStrobePin = D10;
+
+volatile bool strobe_pending = false;
+volatile uint8_t strobe_byte = 0;
+
+void strobeIsr() {
+    strobe_pending = true;
+    strobe_byte = readParallel();
+}
+
+} // namespace
+
+uint8_t readParallel() {
+    uint8_t out = 0;
+    for (int i = 0; i < 8; i++) {
+        if (digitalReadFast(digitalPinToPinName(kParallelDataPins[i])) ==
+            HIGH) {
+            out |= (1 << i);
+        }
+    }
+    if (digitalReadFast(digitalPinToPinName(kParallelStrobePin)) == HIGH) {
+        out |= (1 << 8);
+    }
+    return out;
+}
+
+#define BIT(x, n) ((x & (1 << n)) ? HIGH : LOW)
+
+void writeParallel(uint8_t nibble) {
+    for (int i = 0; i < 4; i++) {
+        int lvl = BIT(nibble, i);
+        if (kParallelNibbleInverted[i]) {
+            lvl = lvl == HIGH ? LOW : HIGH;
+        }
+        digitalWriteFast(digitalPinToPinName(kParallelNibblePins[i]), lvl);
+    }
+}
+
+bool strobeOccurred(uint8_t &byte) {
+    bool pending;
+    {
+        noInterrupts();
+        pending = strobe_pending;
+        byte = strobe_byte;
+        strobe_pending = false;
+        interrupts();
+    }
+
+    return pending;
+}
+
+void setupParallel() {
+    for (int i = 0; i < sizeof(kParallelDataPins) / sizeof(int); i++) {
+        pinMode(kParallelDataPins[i], INPUT);
+    }
+    for (int i = 0; i < sizeof(kParallelNibblePins) / sizeof(int); i++) {
+        pinMode(kParallelNibblePins[i], OUTPUT);
+        digitalWrite(kParallelNibblePins[i], HIGH);
+    }
+    pinMode(kParallelStrobePin, INPUT);
+
+    attachInterrupt(digitalPinToInterrupt(kParallelStrobePin), strobeIsr,
+                    FALLING);
+}