Vectronix Terrapin-X laser rangefinder protocol

Author: platypii

app/src/main/java/com/platypii/baseline/lasers/rangefinder/Crc16.java

@@ -0,0 +1,30 @@
+package com.platypii.baseline.lasers.rangefinder;
+
+class Crc16 {
+    /**
+     * Computes the CRC16 checksum for a given byte array.
+     */
+    public static short crc16(byte[] byteArray) {
+        int crc = 0xffff;
+
+        // Process bytes in pairs (LSB first)
+        for (int i = 0; i < byteArray.length; i++) {
+            int b = byteArray[i] & 0xff;
+            crc ^= b;
+
+            // Process each bit
+            for (int j = 0; j < 8; j++) {
+                if ((crc & 0x0001) != 0) {
+                    crc = (crc >> 1) ^ 0x8408;  // 0x8408 is reversed polynomial
+                } else {
+                    crc = crc >> 1;
+                }
+            }
+        }
+
+        // XOR with 0xfff
+        crc ^= 0xffff;
+
+        return (short) crc;
+    }
+}

app/src/main/java/com/platypii/baseline/lasers/rangefinder/RangefinderService.java

@@ -30,6 +30,7 @@ public class RangefinderService {
     private final BleProtocol protocols[] = {
             new ATNProtocol(),
             new SigSauerProtocol(),
+            new TerrapinProtocol(),
             new UineyeProtocol()
     };
 

app/src/main/java/com/platypii/baseline/lasers/rangefinder/TerraSentenceIterator.java

@@ -0,0 +1,66 @@
+package com.platypii.baseline.lasers.rangefinder;
+
+import android.util.Log;
+import androidx.annotation.NonNull;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+// Sentences start with 7e and end with 7e
+// Sometimes 1 sentence takes 2 messages
+// Sometimes 2 sentences come in 1 message
+class TerraSentenceIterator implements Iterator<byte[]> {
+    private static final String TAG = "TerraSentenceIterator";
+
+    @NonNull
+    private final List<Byte> byteBuffer = new ArrayList<>();
+
+    // Sentences ready to read
+    @NonNull
+    private final List<byte[]> sentences = new ArrayList<>();
+
+    private int state = 0;
+
+    void addBytes(@NonNull byte[] bytes) {
+        for (byte b : bytes) {
+            addByte(b);
+        }
+    }
+
+    private void addByte(byte b) {
+        byteBuffer.add(b);
+        if (state == 0) {
+            if (b == 0x7e) state = 1;
+            else Log.e(TAG, "missing preamble");
+        } else if (state == 1) {
+            if (b == 0x7e) {
+                addSentence();
+                state = 0;
+            }
+        }
+    }
+
+    private void addSentence() {
+        byte[] sent = new byte[byteBuffer.size() - 2];
+        for (int i = 0; i < byteBuffer.size() - 2; i++) {
+            sent[i] = byteBuffer.get(i + 1);
+        }
+        sentences.add(sent);
+        byteBuffer.clear();
+    }
+
+    @Override
+    public boolean hasNext() {
+        return !sentences.isEmpty();
+    }
+
+    @Override
+    public byte[] next() {
+        return sentences.remove(0);
+    }
+
+    @Override
+    public void remove() {
+        throw new UnsupportedOperationException();
+    }
+}