Bus health

The Bus health view of a connection shows how well the bus works over the last minute, ten minutes or hour: its error state, error frames, the error counters of the CAN controller and the bus load.

Error state

CAN controllers count transmit (TEC) and receive (REC) errors and change their state with them:

State	When	Effect
Error active	Both counters below 96	Normal operation
Error warning	A counter at 96 or above	Still normal; a sign of trouble
Error passive	A counter at 128 or above	The controller only sends passive error flags and waits longer before sending
Bus off	TEC at 256 or above	The controller does not take part in the bus until it is restarted

The card at the top shows the current state; the timeline below shows the state of every second of the chosen window, and the cards count the error frames and how often the bus went bus off or error passive.

The state comes from the error frames, which the interface reports in the SocketCAN layout (SocketCAN on Linux, and interfaces using it such as gs_usb, PCAN or Kvaser with SocketCAN drivers): bus off, controller restarted, error warning and passive, and the TEC and REC when the driver includes them. Interfaces reporting their state through python-can (e.g. PCAN on Windows) are used too.

Error frames on Linux

SocketCAN delivers error frames only when they are enabled, and many drivers report the error counters only with berr-reporting: sudo ip link set can0 type can bitrate 500000 berr-reporting on restart-ms 100. Without error frames the state stays unknown (or active while frames flow).

Charts

• Bus load in percent (or frames per second when the bitrate is unknown), with its peak in the window.
• Error frames per second; over 10 minutes and an hour each point covers 5 or 30 seconds and shows the peak of that time, so short bursts stay visible.
• TEC and REC, when the interface reports them.

1 min, 10 min and 1 h choose the window. The history covers the last hour while the connection exists, also while the view is not shown; Reset forgets it.

Error events

The list at the bottom shows the latest error frames, decoded: the error class (e.g. bus off, no acknowledgement, lost arbitration), controller problems (RX buffer overflow, TX error passive, back to error active), protocol violations (bit stuffing error, frame format error, unable to send dominant bit) and the counters. The trace shows the same text in the Info column of error frames.