crc in protocol

protocol.py

@@ -2,27 +2,57 @@ import serial
 import struct
 import time
 
+def crc8(data: bytes) -> int:
+    crc = 0x00
+    for byte in data:
+        crc ^= byte
+        for _ in range(8):
+            if crc & 0x80: crc = ((crc << 1) & 0xFF) ^ 0x07
+            else: crc = (crc << 1) & 0xFF
+    return crc
+
 class I2CPCClient:
     def __init__(self, port, baudrate=115200, timeout=1):
         self.ser = serial.Serial(port=port, baudrate=baudrate, timeout=timeout)
-        self.ser.write(b"~/")
-        while not ((d := self.ser.read_all()) and (b"\x01" in d or b"\xff" in d)): time.sleep(0.01)
 
-    def _send_packet(self, payload: bytes):
-        self.ser.write(bytes([len(payload)]) + payload)
+        # Gurantees resync
+        self.ser.write(b"~/")
+        self.ser.write(b"\x00"*64)
+        self.ser.flush()
+        self.ser.write(b"~/")
+        self.ser.flush()
+        while not ((d := self.ser.read_all()) and b"\xff" in d): time.sleep(0.01)
+
+    def _send_packet(self, payload: bytes, crc: bool = True):
+        if len(payload) > 127: raise ValueError("Payload too large")
+
+        length_byte = len(payload) | (0x80 if crc else 0x00)
+        data = bytes([length_byte]) + payload
+        if crc: data += bytes([crc8(data)])
+        self.ser.write(data)
 
         # Read response length
         resp_len_raw = self.ser.read(1)
-        if not resp_len_raw:
-            raise TimeoutError("Error")
+        if not resp_len_raw: raise TimeoutError("No response")
 
         resp_len = resp_len_raw[0]
-        response = self.ser.read(resp_len)
+        resp_has_crc = bool(resp_len & 0x80)
+        resp_len &= 0x7F
 
-        if len(response) != resp_len: raise TimeoutError("Incomplete response")
+        total_to_read = resp_len + (1 if resp_has_crc else 0)
+
+        response = self.ser.read(total_to_read)
+        if len(response) != total_to_read: raise TimeoutError("Incomplete response")
+
+        if resp_has_crc:
+            received_crc = response[-1]
+            body = resp_len_raw + response[:-1]
+            if crc8(body) != received_crc: raise ValueError("CRC mismatch")
+            response = response[:-1]
 
         return response
   
+
     def set_clock(self, clock_hz: int):
         payload = bytes([0]) + struct.pack(">I", clock_hz)
         return self._send_packet(payload)
@@ -48,6 +78,8 @@ class I2CPCClient:
 
     def reboot(self): return self._send_packet(bytes([5]))
 
+    def get_persistence_address(self): return self._send_packet(bytes([0xfe]))
+
     def set_baudrate(self, baud: int):
         payload = bytes([6]) + struct.pack(">I", baud)
         out = self._send_packet(payload)

test.py

@@ -2,6 +2,7 @@ from tef import TEF6686
 from protocol import I2CPCClient
 
 p = I2CPCClient("COM17")
+print(p._send_packet(bytes([4])))
 tef = TEF6686(p)
 tef.init()
 tef.FM_Tune_To(1, 9500)