From 194cf31425c9759a0a579fdc36f75889f4e4ee92 Mon Sep 17 00:00:00 2001
From: gpotter2 <10530980+gpotter2@users.noreply.github.com>
Date: Fri, 28 Aug 2026 17:01:43 +0200
Subject: [PATCH] xcp: proper fix

AI-Assisted: no
---
 scapy/contrib/automotive/xcp/cto_commands_slave.py |  2 +-
 scapy/contrib/automotive/xcp/xcp.py                | 12 ++++++++++++
 test/contrib/automotive/xcp/xcp.uts                |  8 --------
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/scapy/contrib/automotive/xcp/cto_commands_slave.py b/scapy/contrib/automotive/xcp/cto_commands_slave.py
index e4bcc1d4798..20e042d73aa 100644
--- a/scapy/contrib/automotive/xcp/cto_commands_slave.py
+++ b/scapy/contrib/automotive/xcp/cto_commands_slave.py
@@ -85,7 +85,7 @@ def post_dissection(self, pkt):
             conf.contribs["XCP"][
                 "Address_Granularity_Byte"] = self.get_address_granularity()
 
-        if conf.contribs["XCP"]["allow_cto_and_dto_change"] and self.max_cto != 0:
+        if conf.contribs["XCP"]["allow_cto_and_dto_change"]:
             conf.contribs["XCP"]["MAX_CTO"] = self.max_cto
             conf.contribs["XCP"]["MAX_DTO"] = self.max_dto or self.max_dto_le
 
diff --git a/scapy/contrib/automotive/xcp/xcp.py b/scapy/contrib/automotive/xcp/xcp.py
index dcadac43894..d724154f256 100644
--- a/scapy/contrib/automotive/xcp/xcp.py
+++ b/scapy/contrib/automotive/xcp/xcp.py
@@ -6,6 +6,18 @@
 
 # scapy.contrib.description = Universal calibration and measurement protocol (XCP) # noqa: E501
 # scapy.contrib.status = loads
+
+"""
+Universal calibration and measurement protocol (XCP)
+
+When using this module, one must at least define the following values:
+
+    >>> # These are example values, please change them to your setup.
+    >>> conf.contribs["XCP"]["MAX_CTO"] = 255
+    >>> conf.contribs["XCP"]["MAX_DTO"] = 65535
+    >>> conf.contribs["XCP"]["Address_Granularity_Byte"] = 4
+"""
+
 import struct
 
 from scapy.config import conf
diff --git a/test/contrib/automotive/xcp/xcp.uts b/test/contrib/automotive/xcp/xcp.uts
index 279df4aced2..499977d247f 100644
--- a/test/contrib/automotive/xcp/xcp.uts
+++ b/test/contrib/automotive/xcp/xcp.uts
@@ -12,14 +12,6 @@ load_layer("can", globals_dict=globals())
 conf.contribs['CAN']['swap-bytes'] = False
 load_contrib("automotive.xcp.xcp",  globals_dict=globals())
 
-= Reject a zero MAX_CTO response before changing state
-conf.contribs["XCP"]["MAX_CTO"] = None
-request = CTORequest()/Connect()
-response = CTOResponse(bytes.fromhex("ffff000000000101"))
-assert not response.answers(request)
-assert conf.contribs["XCP"]["MAX_CTO"] is None
-
-
 = Test padding
 
 conf.contribs["XCP"]["add_padding_for_can"] = True