How to compare two ARXML files

Why a text diff is the wrong tool

Exporting tools regenerate UUIDs, reorder elements, change indentation and timestamps. Between the two sample extracts of ARXML Compare (an ECU extract, version 1 and version 2, with new UUIDs), git diff --no-index --numstat counts 1,140 changed lines: 605 added, 535 removed.

The real changes are 23. And a text diff cannot tell you that a signal moved from one PDU to another: it shows a block removed in one place and a block added elsewhere.

Compare by AR-PATH, not by line

• Match each element by its AR-PATH, the path of SHORT-NAMEs from the root, so the order of the file does not matter.
• Ignore UUIDs, ADMIN-DATA and timestamps, and by default descriptions: they change at each export.
• Compare numbers by value: 0x2A1 and 673 are the same CAN ID, 0x10 and 16 the same value.
• Follow the references: a signal's PDU and start bit live in the mapping of the PDU, a frame's ID in its triggering.
• Know the limits: a renamed or moved element shows as removed and added, and variants are compared as written.

Step by step in VS Code

1. Install ARXML Compare, free, from the VS Code Marketplace.
2. Select the old and then the new file in the Explorer, right-click, “Compare Selected ARXML Files”. For an extract split into several files, open each folder as one model.
3. The free version shows how many signals, PDUs, frames, ports and components were added, removed or modified, or that nothing changed.
4. Pro shows each change with its before and after values, opens it at its line in either file, lists the ports affected by a changed interface, and writes the report to Excel, CSV or HTML.

A real example

The mapping of the signal DoorLockSts_FL in version 1, inside PDU BCM_Status_01:

<I-SIGNAL-TO-I-PDU-MAPPING UUID="u-00000096">
  <SHORT-NAME>DoorLockSts_FL_ISM</SHORT-NAME>
  <I-SIGNAL-REF DEST="I-SIGNAL">/NovairSample/Signals/DoorLockSts_FL</I-SIGNAL-REF>
  <PACKING-BYTE-ORDER>MOST-SIGNIFICANT-BYTE-LAST</PACKING-BYTE-ORDER>
  <START-POSITION>12</START-POSITION>
  <TRANSFER-PROPERTY>TRIGGERED-ON-CHANGE</TRANSFER-PROPERTY>
</I-SIGNAL-TO-I-PDU-MAPPING>

The same mapping in version 2, with a new UUID, now inside PDU BCM_Status_02:

<I-SIGNAL-TO-I-PDU-MAPPING UUID="v-000000a2">
  <SHORT-NAME>DoorLockSts_FL_ISM</SHORT-NAME>
  <I-SIGNAL-REF DEST="I-SIGNAL">/NovairSample/Signals/DoorLockSts_FL</I-SIGNAL-REF>
  <PACKING-BYTE-ORDER>MOST-SIGNIFICANT-BYTE-LAST</PACKING-BYTE-ORDER>
  <START-POSITION>4</START-POSITION>
  <TRANSFER-PROPERTY>TRIGGERED-ON-CHANGE</TRANSFER-PROPERTY>
</I-SIGNAL-TO-I-PDU-MAPPING>

What ARXML Compare counts between the two files (free):

Before: novair-sample-body-ecu_v1.arxml
After:  novair-sample-body-ecu_v2.arxml
291 elements compared by AR-PATH

Signals                 4 added   2 removed   6 modified
PDUs                    1 added   0 removed   2 modified
Frames                  0 added   0 removed   3 modified
Ports and interfaces    1 added   0 removed   1 modified
Components              0 added   0 removed   1 modified
Other                   0 added   1 removed   1 modified
Total: 23

And the first changes it lists, with their before and after values (Pro):

modified  AmbLightDimLvl       Factor: 0.4 -> 0.5
modified  DoorLockSts_FL       PDU: BCM_Status_01 -> BCM_Status_02; Start bit: 12 -> 4
removed   FogLampRearSts       PDU: BCM_Status_02 -> -; Start bit: 48 -> -
modified  HornReq              Transfer property: PENDING -> TRIGGERED-ON-CHANGE
modified  IntLightDimLvl       Factor: 0.4 -> 0.5
removed   KeyFobBattLow        PDU: BCM_Status_01 -> -; Start bit: 24 -> -
added     RearDefrostSts       PDU: - -> BCM_Comfort_03; Start bit: - -> 0
added     SeatHeatLvl_FL       PDU: - -> BCM_Comfort_03; Start bit: - -> 8
added     SeatHeatLvl_FR       PDU: - -> BCM_Comfort_03; Start bit: - -> 16

So: DoorLockSts_FL moved from BCM_Status_01 to BCM_Status_02, start bit 12 to 4; frame FR_BCM_Lights_01 changed its ID from 0x2A1 to 0x2A4; and in the ports, interface If_SR_0 changed a data element type from uint8 to uint16, which affects one port that did not change itself.

What is compared, and what is not

Compared: signals, PDUs, frames (CAN, CAN FD, LIN, FlexRay), ports and interfaces, software components, and every other element that has a SHORT-NAME, by AR-PATH and in any order. Ignored: UUIDs, ADMIN-DATA, timestamps and, by default, descriptions. Not compared: ECUC configuration values. A renamed or moved element shows as removed and added. Variants are compared as written, not resolved. Tables read AUTOSAR 4 files (schema r4.0); AUTOSAR 3 files open in the tree only. Ethernet: PDUs only, with no table for sockets or SOME/IP services (their changes appear under Other).

Errors and warnings during a comparison

The messages ARXML Compare shows, produced by its own code from its test files:

• One side is not well-formed XML: “Comparison stopped: malformed.arxml is not well-formed XML at line 290, column 17. A partial file is never compared.”
• The same file on both sides: “Before and after are the same files. Choose two different versions.”
• Before and after use different AUTOSAR schemas: “Before and after use different schemas (AUTOSAR_323 → AUTOSAR_00051). Elements are compared by AR-PATH: an element type renamed between schemas shows as removed and added.”
• An extract split into files that disagree: “/Conf/Shared is defined differently in a.arxml (line 9) and b.arxml (line 9). The comparison uses a.arxml.”

A comparison never runs on a partial file: if one side is not well-formed, it stops and says where.

Frequently asked questions