Acceptance Filtering Ixxat USB-to-CAN V2 compact Dropping Legitimate Messages

Hi,

I am using an "Ixxat USB-to-CAN V2 compact" to connect to a device where I have to filter out certain messages from other devices using their IDs. I control the USB-to-CAN V2 using the latest VCI 4 C++ SDK from your website.

For filtering, I use the acceptance filter and set the number of filter IDs (dwFilterSize) on the message channel to 0. The filtering is only done in message channels, not on the controller, as eventually, I will open multiple channels on the same controller that will filter for their respective device on the CAN bus.

The filtering mostly works fine, but at high busloads (> 50%, 1000kbit/s), I observe dropped messages that should not have been filtered out. Using a second USB-to-CAN and canAnalyser3 mini I can see that the messages appear on the bus but that they are wrongfully filtered out by the first USB-to-CAN.

If the acceptance filter is set to CAN_FILTER_INCL and the mask is set to CAN_ACC_MASK_ALL (i.e., the filter is active but lets all messages through), the channel receives all messages without dropping any.

Below I attach source code that sets up the filters.

ICanSocket2* pCanSocket
ICanChannel2* pCanChn;

[...]

// Open the first channel in non-exclusive mode
if (pCanSocket->CreateChannel(FALSE, &pCanChn) != VCI_OK)
{
    ReleaseAll();
    return;
}

// Initialize the channel
if (pCanChn->Initialize(2560, 2560, 0, CAN_FILTER_INCL) != VCI_OK)
{
    ReleaseAll();
    return;
}

// Set the acceptance filter
UINT32 code;
UINT32 mask;

// Example values
code = 2;
mask = 3;

// Shift by 1 because the filter for the ID starts at the 1st bit. The 0th bit is for RTR filtering.
UINT32 dwCode = code << 1;
UINT32 dwMask = mask << 1;

if (d_ptr_->pCanChn->SetAccFilter(CAN_FILTER_EXT, dwCode, dwMask) != VCI_OK)
{
    ReleaseAll();
    return;
}

// Activate the CAN channel
if (pCanChn->Activate() != VCI_OK)
{
    ReleaseAll();
    return;
}

Am I doing something wrong during the setup? To me, it almost seems that the driver might throw away certain legitimate messages if it is overwhelmed by the number of messages it has to filter.

Thank you for your help.

Best regards,

Noah

Official comment

Peter Wucherer

August 22, 2025 14:57

Hi Noah,

it's an interesting problem. I will try to reproduce it here. But I need some time for this and add then next week more information here.

Best regards,
Peter

Noah Berner

August 22, 2025 15:24

Hi Peter,

Thank you for taking on the problem. I look forward to your next post.

Best regards,

August 25, 2025 10:57

Hi Noah,

I try to reproduce it. But I did not see lost data with your filter settings, all messages are received.
I send 204800 messages at 1 MBit with nearly 100% bus load and incremented identifier. And there I get all 51200 expected messages.
Only when I use "printf" to write to the console I lose a lot of data because it's too slow.

I cannot add on this forum site the example. Maybe you create a support ticket, and I send you my demo source code there.
https://support.hms-networks.com/hc/en-us

Best regards,
Peter

August 25, 2025 11:21

Hi Peter,

Thank you for your help. I have opened a ticket to receive your souce code.

Acceptance Filtering Ixxat USB-to-CAN V2 compact Dropping Legitimate Messages

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