diff --git a/README.md b/README.md
index ec36923..d7fbe2a 100644
--- a/README.md
+++ b/README.md
@@ -222,6 +222,50 @@ Example:
 $ ./dmctl.py --conn cafe:1312 get-device-info
 ```
 
+### SUMP Logic Analyzer mode
+
+The device can act as a logic analyzer, implementing the SUMP protocol. It
+first needs to be put into mode 4, which can be done using the following
+command:
+
+```
+$ ./dmctl.sh set-mode 4
+```
+
+As soon as this is done, the SUMP logic analyzer should be available on the
+first USB-CDC interface of the device. It can be used with a connection string
+such as `ols:conn=/dev/ttyACM0` in sigrok and PulseView.
+
+### XVC2DAP
+
+`xvc2dap.py` is a Python script that implements a Xilinx Virtual Cable server
+and talks to a CMSIS-DAP device, acting like a bridge between the two. This way,
+you can use any CMSIS-DAP device (including this project) as a fake Xilinx
+Platform Cable.
+
+It requires pyOCD as a dependency (for its builtin `pydapaccess` module).
+
+Usage:
+
+```
+$ ./xvc2dap.py --help
+usage: xvc2dap.py [-h] [--serial SERIAL] address [port]
+
+positional arguments:
+  address          Host to bind to, for the XVC server, default localhost
+  port             port to bind to, for the XVC server, default 2542
+
+optional arguments:
+  -h, --help       show this help message and exit
+  --serial SERIAL  Connection string to the CMSIS-DAP device, as a serial
+                   number, defaults to the first device found.
+```
+
+### USB Vendor interface protocol
+
+The USB vendor interface protocol is described
+[here](./wiki/USB-config-%26-command-protocol) in the wiki.
+
 ## License
 
 TinyUSB is licensed under the [MIT license](https://opensource.org/licenses/MIT).
diff --git a/host/xvc2dap.py b/host/xvc2dap.py
index 37ed563..54d2603 100755
--- a/host/xvc2dap.py
+++ b/host/xvc2dap.py
@@ -6,8 +6,6 @@ import struct
 
 from typing import *
 
-from pyocd.probe.pydapaccess import *
-
 
 class EndOfStreamException(Exception): pass
 
@@ -67,14 +65,16 @@ def dap_split_jseq(nbits: int, tms: bytes, tdi: bytes) -> List[JtagSeq]:
     return res
 
 
-def get_dap(serial: Optional[str]) -> DAPAccess:
+def get_dap(serial: Optional[str]) -> Any:  #DAPAccess:
+    import pyocd.probe.pydapaccess as pydap
+
     if serial is not None:
         try:
-            return DAPAccess.get_device(serial)
+            return pydap.DAPAccess.get_device(serial)
         except Exception:# as e:
             raise Exception("Could not find CMSIS-DAP device %s" % serial)
     else:
-        devs = DAPAccess.get_connected_devices()
+        devs = pydap.DAPAccess.get_connected_devices()
         if len(devs) == 1:
             return devs[0]
         elif len(devs) == 0:
@@ -97,7 +97,7 @@ def xvc_read_cmd(f) -> bytes:
             r += bv
 
 
-def xvc_do_cmd(cmd, f, dap):
+def xvc_do_cmd(cmd: bytes, f, dap):
     if cmd == b"getinfo":
         # parameter is max vector len (in bits)
         # we use some value here (2k should be good enough), though in reality
@@ -192,13 +192,19 @@ def xvc2dap_do(args: Any) -> int:
 
 
 def main() -> int:
+    try:
+        import pyocd.probe.pydapaccess
+    except ImportError:
+        print("WARNING: pyocd module not found (not installed?), xvc2dap.py "+\
+              "will not work.")
+
     parser = argparse.ArgumentParser()
 
     parser.add_argument('--serial', type=str, default=None,
                         help="Connection string to the CMSIS-DAP device, as "+\
                         "a serial number, defaults to the first device found.")
 
-    parser.add_argument('address', type=str, default='localhost',
+    parser.add_argument('address', type=str, default='localhost', nargs='?',
                         help="Host to bind to, for the XVC server, default "+\
                              "localhost")
     parser.add_argument('port', type=int, default=2542, nargs='?',