Improve gs_usb usability and fix loopback frames (#1270)

* Improve gs_usb usability and fix loopback frames

* Fix extended id parsing

* Fix formatting

Author: chemicstry

can/interfaces/gs_usb.py

@@ -1,7 +1,7 @@
 from typing import Optional, Tuple
 
 from gs_usb.gs_usb import GsUsb
-from gs_usb.gs_usb_frame import GsUsbFrame
+from gs_usb.gs_usb_frame import GsUsbFrame, GS_USB_NONE_ECHO_ID
 from gs_usb.constants import CAN_ERR_FLAG, CAN_RTR_FLAG, CAN_EFF_FLAG, CAN_MAX_DLC
 import can
 import usb
@@ -14,17 +14,42 @@
 
 
 class GsUsbBus(can.BusABC):
-    def __init__(self, channel, bus, address, bitrate, can_filters=None, **kwargs):
+    def __init__(
+        self,
+        channel,
+        bitrate,
+        index=None,
+        bus=None,
+        address=None,
+        can_filters=None,
+        **kwargs,
+    ):
         """
         :param channel: usb device name
+        :param index: device number if using automatic scan, starting from 0.
+            If specified, bus/address shall not be provided.
         :param bus: number of the bus that the device is connected to
         :param address: address of the device on the bus it is connected to
         :param can_filters: not supported
         :param bitrate: CAN network bandwidth (bits/s)
         """
-        gs_usb = GsUsb.find(bus=bus, address=address)
-        if not gs_usb:
-            raise CanInitializationError(f"Cannot find device {channel}")
+        if (index is not None) and ((bus or address) is not None):
+            raise CanInitializationError(
+                f"index and bus/address cannot be used simultaneously"
+            )
+
+        if index is not None:
+            devs = GsUsb.scan()
+            if len(devs) <= index:
+                raise CanInitializationError(
+                    f"Cannot find device {index}. Devices found: {len(devs)}"
+                )
+            gs_usb = devs[index]
+        else:
+            gs_usb = GsUsb.find(bus=bus, address=address)
+            if not gs_usb:
+                raise CanInitializationError(f"Cannot find device {channel}")
+
         self.gs_usb = gs_usb
         self.channel_info = channel
 
@@ -100,13 +125,13 @@ def _recv_internal(
         msg = can.Message(
             timestamp=frame.timestamp,
             arbitration_id=frame.arbitration_id,
-            is_extended_id=frame.can_dlc,
+            is_extended_id=frame.is_extended_id,
             is_remote_frame=frame.is_remote_frame,
             is_error_frame=frame.is_error_frame,
             channel=self.channel_info,
             dlc=frame.can_dlc,
             data=bytearray(frame.data)[0 : frame.can_dlc],
-            is_rx=True,
+            is_rx=frame.echo_id == GS_USB_NONE_ECHO_ID,
         )
 
         return msg, False

doc/interfaces/gs_usb.rst

@@ -7,7 +7,15 @@ Windows/Linux/Mac CAN driver based on usbfs or WinUSB WCID for Geschwister Schne
 
 Install: ``pip install "python-can[gs_usb]"``
 
-Usage: pass ``bus`` and ``address`` to open the device. The parameters can be got by ``pyusb`` as shown below:
+Usage: pass device ``index`` (starting from 0) if using automatic device detection:
+
+::
+
+    import can
+
+    bus = can.Bus(bustype="gs_usb", channel=dev.product, index=0, bitrate=250000)
+
+Alternatively, pass ``bus`` and ``address`` to open a specific device. The parameters can be got by ``pyusb`` as shown below:
 
 ::