Add quirk for mbed CMSIS-DAP firmware when filtering by bDeviceClass.

- This fixes pyocd#588. Old "Mbed CMSIS-DAP" firmware has an incorrect device
  class value, so it was being filtered out. This problem only occurred
  on Linux.
- Added a common filter_device_by_class() function that checks the
  bDeviceClass value and also applies any quirks.
- Renamed filter_device() to filter_device_by_usage_page().

pyocd/probe/pydapaccess/interface/common.py

@@ -14,7 +14,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# USB class codes.
 USB_CLASS_COMPOSITE = 0x00
+USB_CLASS_COMMUNICATIONS = 0x02
 USB_CLASS_MISCELLANEOUS = 0xef
 
 CMSIS_DAP_USB_CLASSES = [
@@ -25,14 +27,36 @@
 NXP_VID = 0x1fc9
 NXP_LPCLINK2_PID = 0x0090
 
+ARM_VID = 0x0d28
+DAPLINK_PID = 0x0204
+
 CMSIS_DAP_HID_USAGE_PAGE = 0xff00
 
-def filter_device(vid, pid, usage_page):
-    """! @brief Test whether the device should be ignored.
+def filter_device_by_class(vid, pid, device_class):
+    """! @brief Test whether the device should be ignored by comparing bDeviceClass.
+    
+    This function checks the device's bDeviceClass to determine whether the it is likely to be
+    a CMSIS-DAP device. It uses the vid and pid for device-specific quirks.
+    
+    @retval True Skip the device.
+    @retval False The device is valid.
+    """
+    # Check valid classes for CMSIS-DAP firmware.
+    if device_class in CMSIS_DAP_USB_CLASSES:
+        return False
+    # Old "Mbed CMSIS-DAP" firmware has an incorrect bDeviceClass.
+    if (vid == ARM_VID) and (pid == DAPLINK_PID) and (device_class == USB_CLASS_COMMUNICATIONS):
+        return False
+    # Any other class indicates the device is not CMSIS-DAP.
+    return True
+
+def filter_device_by_usage_page(vid, pid, usage_page):
+    """! @brief Test whether the device should be ignored by comparing the HID usage page.
     
-    This function performs device-specific tests to determine whether the device is
-    a CMSIS-DAP interface. An example is the NXP LPC-Link2, which has extra HID interfaces
-    with usage pages other than 0xff00.
+    This function performs device-specific tests to determine whether the device is a CMSIS-DAP
+    interface. The only current test is for the NXP LPC-Link2, which has extra HID interfaces with
+    usage pages other than 0xff00. No generic tests are done regardless of VID/PID, because it is
+    not clear whether all CMSIS-DAP devices have the usage page set to the same value.
     
     @retval True Skip the device.
     @retval False The device is valid.

pyocd/probe/pydapaccess/interface/hidapi_backend.py

@@ -15,7 +15,7 @@
 # limitations under the License.
 
 from .interface import Interface
-from .common import filter_device
+from .common import filter_device_by_usage_page
 from ..dap_access_api import DAPAccessIntf
 from ....utility.compatibility import to_str_safe
 import logging
@@ -78,7 +78,7 @@ def get_all_connected_interfaces():
             pid = deviceInfo['product_id']
 
             # Perform device-specific filtering.
-            if filter_device(vid, pid, deviceInfo['usage_page']):
+            if filter_device_by_usage_page(vid, pid, deviceInfo['usage_page']):
                 continue
 
             try:

pyocd/probe/pydapaccess/interface/pyusb_backend.py

@@ -15,7 +15,7 @@
 # limitations under the License.
 
 from .interface import Interface
-from .common import CMSIS_DAP_USB_CLASSES
+from .common import filter_device_by_class
 from ..dap_access_api import DAPAccessIntf
 import logging
 import os
@@ -257,7 +257,7 @@ def __init__(self, serial=None):
     def __call__(self, dev):
         """Return True if this is a DAP device, False otherwise"""
         # Check if the device class is a valid one for CMSIS-DAP.
-        if dev.bDeviceClass not in CMSIS_DAP_USB_CLASSES:
+        if filter_device_by_class(dev.idVendor, dev.idProduct, dev.bDeviceClass):
             return False
 
         try:

pyocd/probe/pydapaccess/interface/pyusb_v2_backend.py

@@ -15,7 +15,7 @@
 # limitations under the License.
 
 from .interface import Interface
-from .common import CMSIS_DAP_USB_CLASSES
+from .common import filter_device_by_class
 from ..dap_access_api import DAPAccessIntf
 from ... import common
 import logging
@@ -266,7 +266,7 @@ def __init__(self, serial=None):
     def __call__(self, dev):
         """! @brief Return True if this is a CMSIS-DAPv2 device, False otherwise"""
         # Check if the device class is a valid one for CMSIS-DAP.
-        if dev.bDeviceClass not in CMSIS_DAP_USB_CLASSES:
+        if filter_device_by_class(dev.idVendor, dev.idProduct, dev.bDeviceClass):
             return False
 
         try:

pyocd/probe/pydapaccess/interface/pywinusb_backend.py

@@ -15,7 +15,7 @@
 # limitations under the License.
 
 from .interface import Interface
-from .common import filter_device
+from .common import filter_device_by_usage_page
 from ..dap_access_api import DAPAccessIntf
 from ....utility.timeout import Timeout
 import logging
@@ -114,7 +114,7 @@ def get_all_connected_interfaces():
                 dev.open(shared=True)
 
                 # Perform device-specific filtering.
-                if filter_device(dev.vendor_id, dev.product_id, dev.hid_caps.usage_page):
+                if filter_device_by_usage_page(dev.vendor_id, dev.product_id, dev.hid_caps.usage_page):
                     dev.close()
                     continue