Capability 002: Activity Indicator

Status: Accepted

Context

An LED shows at a glance whether the Bridge is alive and whether it is relaying messages. The Bridge relays messages as specified in capability 001.

Functional Requirements

1. Before its initialization is complete, the Bridge keeps the LED off.
2. While messages arrive, each message received on the CAN bus toggles the LED. Only messages that pass the acceptance filter count (capability 001, Functional Requirement 4).
3. When no message has arrived for 1 s, the LED shows a heartbeat: on for 0.1 s, once per second.

Non-Functional Requirements

None.

Error Handling

None.

Solution Constraints

1. The LED is the on-board LED at PC13, active-high.
2. The CAN receive interrupt only counts messages; the main loop drives the LED.
3. Time comes from the system tick; no additional timer.

Out of Scope

• Messages received on the UARTs: the boards send odometry every 10 ms on their own, so the LED would never show whether the Bridge relays anything.
• An error indication

Acceptance Criteria

1. Before initialization: the LED is off.
2. Initialized, no message yet: the LED is on for 0.1 s once per second.
3. Each received CAN message toggles the LED.
4. 1 s after the last received CAN message: the heartbeat resumes.

Decisions

1. Toggling per message is visible at the load of capability 001 (one drive command every 250 ms). Should rates rise, a fixed-rate activity blink replaces it.