Com_SendSignal called. No CAN frame?
A signal write and a bus transmission are different events. Trace the active configuration and runtime gates.
Start with the signal write
Com_SendSignal handles a configured signal in COM. Its return value is not proof that a frame reached the wire. Check the API result and the applicable AUTOSAR release's behaviour. For example, stopped I-PDU groups and busy large-data handling have distinct return conditions.
Check mode and transfer property
The active transmission mode controls periodic, direct, mixed or no transmission behaviour. A triggered-on-change transfer property depends on a value change; repeating the same value need not trigger a direct request. Mixed mode can still transmit periodically. Filters, repetition and minimum delay time must be considered in their configured context.
Continue through lower layers
Check that the relevant Tx I-PDU group is started, communication is permitted and the controller is operational. Trace COM to PduR to CanIf to the driver according to the configured route. Request acceptance, confirmation and a captured frame are separate observations. Buffering, scheduling and bus arbitration can affect when the frame is seen.
Std_ReturnType status = Com_SendSignal(SignalId, &value);
/* Inspect status, active I-PDU group and Tx mode. */
/* Correlate lower-layer requests with a bus trace. */Follow the transmission
Application / RTE
The application updates its communication value.
Conceptual sequence. Timing is slowed for learning; it is not a hardware measurement.
Your investigation
A TRIGGERED_ON_CHANGE signal is written with the same value twice in mixed mode. Explain why you might still see a later frame.
Reveal the investigation checklist
- Compare the old and new signal values.
- Read the selected Tx mode and periodic cycle.
- Inspect active I-PDU group and minimum delay timing.
- Correlate COM requests, confirmations and bus timestamps.
Does every successful signal update imply an immediate CAN frame?
Answer the knowledge check correctly to complete this lesson.
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