Implementing Checksum Algorithm E2E Profile 5 with NI VCOM RBS Descriptor Tool

NI-VCOM defines many common checksum algorithms in the RBS Descriptor tool. The users can implement checksum easily, compared to the custom interface way introduced in Using NI-VCOM Toolkit to Define the Custom Checksum for CAN Application. This article will introduce how to implement E2E Profile 5 with the RBS Descriptor tool.

1. Add the VCOM custom device in VeriStand. Click Create VCOM Descriptor to open the RBSConfig tool.
2. Right-click in the Datapool, then select New Network>>CAN or FlexRay Network>>Create single network to add the database file.
3. Find the checksum signal in the Datapool, then right-click on it and select Copy2Config.

4. Find the checksum signal in the Configuration menu, then click it and choose Change to AutoSignal.

5. In the drop-down menu of Auto Signal type, select ChecksumCCITT. 

• • CRCMask: Determines the data bytes that are used for the CRC calculation. For example, CRCMask 252 (1111 1100 in binary) means that byte 2 to byte 7 of the data bytes will be used for checksum calculation.
  • UserBytesAfter: These bytes are used after the data bytes for the checksum calculation. Data ID can be filled here. The first byte is the low byte of Data ID, and the second byte is the high byte of Data ID.

       Fill the above parameters as shown in the image below, then click Execute.

6. Click the three points on the right side of ChecksumUserBytesAfter to edit the Data ID. 

For example, the Data ID of this frame is 4957 (0x135D in hexadecimal). You should fill the ChecksumUserBytesAfter as shown in the image below.

7. Right-click on the database file in Configuration, then select Save as XML to save the configuration.

Additional Information

If you want to protect bytes 8 to 20 to calculate the checksum, the CRCMask should be 2096896 (1 1111 1111 1111 0000 0000 in binary). There is a known issue that the value of CRCMask is limited to 255, as it is defined as an unsigned 32-bit integer. If you fill a value greater than 255, an error will be triggered when Execute is clicked.

A workaround for this is that you can set a temporary CRCMask value of less than 255. Then, after saving the configuration as an XML file, you can open this file with a text editor (such as Notepad or Notepad++) and manually change the value to the one you require.

Before this modification, the CRCMask parameter in the XML file should appear like the following image:

Then, the following image shows the XML file after modifying this value: