Merge pull request brendan-w#125 from Ircama/headers

alistair23 · web-flow · commit a372044ebbfd · 2018-12-08T08:23:44.000-08:00
Add support of custom headers to OBDCommand
diff --git a/docs/Custom Commands.md b/docs/Custom Commands.md
@@ -10,6 +10,7 @@ If the command you need is not in python-OBDs tables, you can create a new `OBDC
 | decoder              | callable | Function used for decoding messages from the OBD adapter                   |
 | ecu (optional)       | ECU      | ID of the ECU this command should listen to (`ECU.ALL` by default)         |
 | fast (optional)      | bool     | Allows python-OBD to alter this command for efficieny (`False` by default) |
+| header (optional)    | string   | If set, use a custom header instead of the defalut one (7E0)               |
 
 
 Example
@@ -95,7 +96,13 @@ The `ecu` argument is a constant used to filter incoming messages. Some commands
 
 ### OBDCommand.fast
 
-The `fast` argument tells python-OBD whether it is safe to append a `"01"` to the end of the command. This will instruct the adapter to return the first response it recieves, rather than waiting for more (and eventually reaching a timeout). This can speed up requests significantly, and is enabled for most of python-OBDs internal commands. However, for unusual commands, it is safest to leave this disabled.
+The optional `fast` argument tells python-OBD whether it is safe to append a `"01"` to the end of the command. This will instruct the adapter to return the first response it recieves, rather than waiting for more (and eventually reaching a timeout). This can speed up requests significantly, and is enabled for most of python-OBDs internal commands. However, for unusual commands, it is safest to leave this disabled.
+
+---
+
+### OBDCommand.header
+
+The optional `header` argument tells python-OBD to use a custom header when querying the command. If not set, python-OBD assumes that the default 7E0 header is needed for querying the command. The switch between default and custom header (and vice versa) is automatically done by python-OBD.
 
 ---
 
diff --git a/obd/OBDCommand.py b/obd/OBDCommand.py
@@ -31,7 +31,7 @@
 ########################################################################
 
 from .utils import *
-from .protocols import ECU
+from .protocols import ECU, ECU_HEADER
 from .OBDResponse import OBDResponse
 
 import logging
@@ -47,14 +47,16 @@ def __init__(self,
                  _bytes,
                  decoder,
                  ecu=ECU.ALL,
-                 fast=False):
+                 fast=False,
+                 header=ECU_HEADER.ENGINE):
         self.name      = name        # human readable name (also used as key in commands dict)
         self.desc      = desc        # human readable description
         self.command   = command     # command string
         self.bytes     = _bytes      # number of bytes expected in return
         self.decode    = decoder     # decoding function
         self.ecu       = ecu         # ECU ID from which this command expects messages from
         self.fast      = fast        # can an extra digit be added to the end of the command? (to make the ELM return early)
+        self.header    = header      # ECU header used for the queries
 
     def clone(self):
         return OBDCommand(self.name,
diff --git a/obd/obd.py b/obd/obd.py
@@ -38,6 +38,7 @@
 from .commands import commands
 from .OBDResponse import OBDResponse
 from .utils import scan_serial, OBDStatus
+from .protocols import ECU_HEADER
 
 logger = logging.getLogger(__name__)
 
@@ -55,6 +56,7 @@ def __init__(self, portstr=None, baudrate=None, protocol=None, fast=True,
         self.fast = fast # global switch for disabling optimizations
         self.timeout = timeout
         self.__last_command = b"" # used for running the previous command with a CR
+        self.__last_header = ECU_HEADER.ENGINE # for comparing with the previously used header
         self.__frame_counts = {} # keeps track of the number of return frames for each command
 
         logger.info("======================= python-OBD (v%s) =======================" % __version__)
@@ -138,6 +140,19 @@ def __load_commands(self):
         logger.info("finished querying with %d commands supported" % len(self.supported_commands))
 
 
+    def __set_header(self, header):
+        if header == self.__last_header:
+            return
+        r = self.interface.send_and_parse(b'AT SH ' + header + b' ')
+        if not r:
+            logger.info("Set Header ('AT SH %s') did not return data", header)
+            return OBDResponse()
+        if "\n".join([ m.raw() for m in r ]) != "OK":
+            logger.info("Set Header ('AT SH %s') did not return 'OK'", header)
+            return OBDResponse()
+        self.__last_header = header
+
+
     def close(self):
         """
             Closes the connection, and clears supported_commands
@@ -147,6 +162,7 @@ def close(self):
 
         if self.interface is not None:
             logger.info("Closing connection")
+            self.__set_header(ECU_HEADER.ENGINE)
             self.interface.close()
             self.interface = None
 
@@ -254,7 +270,8 @@ def query(self, cmd, force=False):
         if not force and not self.test_cmd(cmd):
             return OBDResponse()
 
-        # send command and retrieve message
+        self.__set_header(cmd.header)
+
         logger.info("Sending command: %s" % str(cmd))
         cmd_string = self.__build_command_string(cmd)
         messages = self.interface.send_and_parse(cmd_string)
diff --git a/obd/protocols/__init__.py b/obd/protocols/__init__.py
@@ -30,7 +30,7 @@
 #                                                                      #
 ########################################################################
 
-from .protocol import ECU
+from .protocol import ECU, ECU_HEADER
 
 from .protocol_unknown import UnknownProtocol
 
diff --git a/obd/protocols/protocol.py b/obd/protocols/protocol.py
@@ -45,6 +45,11 @@
 """
 
 
+class ECU_HEADER:
+    """ Values for the ECU headers """
+    ENGINE = b'7E0'
+
+
 class ECU:
     """ constant flags used for marking and filtering messages """
 
