v1.9.14: Senseair S88 - implémentation lecture Modbus RTU

read_co2() lit IR1..IR4 en une trame (status + CO2) à 9600 8N1,
adresse 0xFE 'any address', avec vérification CRC16-Modbus et rejet
de la mesure si status non-nul (warm-up ou erreur).

CRC requête/réponse validés contre les exemples du datasheet TDE14367.
Doc protocole consolidée dans S88/README.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

S88/get_data.py

@@ -2,6 +2,8 @@
 Live read of the Senseair S88 CO2 sensor (used by the web "Get Data" button).
 Prints a JSON object: {"CO2": <int_ppm>} or {"error": "<message>"}.
 
+Modbus RTU 9600 8N1, reads IR1..IR4 in one frame.
+
 Usage: /usr/bin/python3 /var/www/nebuleair_pro_4g/S88/get_data.py [port]
 If no port is given, the script reads S88_port from config_table.
 '''
@@ -16,6 +18,22 @@ DB_PATH = "/var/www/nebuleair_pro_4g/sqlite/sensors.db"
 DEFAULT_PORT = "/dev/ttyAMA5"
 BAUDRATE = 9600
 
+SLAVE_ADDR = 0xFE
+READ_REQUEST = bytes([SLAVE_ADDR, 0x04, 0x00, 0x00, 0x00, 0x04, 0xE5, 0xC6])
+EXPECTED_RESPONSE_LEN = 13
+
+
+def crc16_modbus(data):
+    crc = 0xFFFF
+    for byte in data:
+        crc ^= byte
+        for _ in range(8):
+            if crc & 1:
+                crc = (crc >> 1) ^ 0xA001
+            else:
+                crc >>= 1
+    return crc
+
 
 def get_port_from_config():
     try:
@@ -30,9 +48,33 @@ def get_port_from_config():
 
 
 def read_co2(ser):
-    # TODO: implement the Senseair S88 read protocol once the datasheet is provided.
-    # Expected return: integer CO2 concentration in ppm, or None on failure.
-    raise NotImplementedError("Senseair S88 read protocol not implemented yet")
+    ser.reset_input_buffer()
+    ser.write(READ_REQUEST)
+    response = ser.read(EXPECTED_RESPONSE_LEN)
+
+    if len(response) < 5:
+        return None, f"short response ({len(response)} bytes)"
+
+    if response[1] & 0x80:
+        return None, f"Modbus exception code {response[2]:#04x}"
+
+    if len(response) != EXPECTED_RESPONSE_LEN:
+        return None, f"unexpected response length {len(response)}"
+
+    received_crc = response[-2] | (response[-1] << 8)
+    if crc16_modbus(response[:-2]) != received_crc:
+        return None, "CRC mismatch"
+
+    if response[0] != SLAVE_ADDR or response[1] != 0x04 or response[2] != 0x08:
+        return None, f"unexpected header {response[:3].hex()}"
+
+    status = (response[3] << 8) | response[4]
+    co2 = (response[9] << 8) | response[10]
+
+    if status != 0:
+        return None, f"sensor not ready (status={status:#06x})"
+
+    return co2, None
 
 
 def main():
@@ -52,13 +94,11 @@ def main():
         return
 
     try:
-        co2 = read_co2(ser)
+        co2, err = read_co2(ser)
         if co2 is None:
-            print(json.dumps({"error": "No data from S88"}))
+            print(json.dumps({"error": err or "No data from S88"}))
             return
         print(json.dumps({"CO2": int(round(co2))}))
-    except NotImplementedError as e:
-        print(json.dumps({"error": str(e)}))
     except Exception as e:
         print(json.dumps({"error": f"S88 read error: {e}"}))
     finally: