# Svc::ComAggregator

Aggregates buffers in the downlink chain. This is for use with systems that have fixed size frames (e.g. CCSDS TM) that needed internal aggregation.

> [!CAUTION]
> `Svc::ComAggregator` does not preserve context.

## Requirements

| ID                    | Description                                                                                                                                                   | Verification |
| --------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------ |
| Svc-ComAggregator-001 | ComAggregator shall accept incoming downlink data as `Fw::Buffer`, `ComCfg::FrameContext` pairs and append the buffer into the aggregate space permitting     | Unit-Test    |
| Svc-ComAggregator-002 | ComAggregator shall hold the incoming buffer when there is insufficient space in the aggregate buffer.                                                        | Unit-Test    |
| Svc-ComAggregator-003 | ComAggregator shall send the current aggregate buffer when the incoming buffer is held due to overflow.                                                       | Unit-Test    |
| Svc-ComAggregator-004 | ComAggregator shall send the current aggregate buffer when it receives a timeout trigger if and only if the aggregate is non-empty.                           | Unit-Test    |
| Svc-ComAggregator-005 | ComAggregator shall clear aggregation state when a `Fw::Success::SUCCESS` communication status is received back.                                                             | Unit-Test    |
| Svc-ComAggregator-006 | ComAggregator shall preserve the order of received buffers when forming each aggregate and across aggregate sends.                                            | Unit-Test    |
| Svc-ComAggregator-007 | ComAggregator shall interoperate with the [Communication Adapter Interface protocol](../../../docs/reference/communication-adapter-interface.md). Specifically, it shall pass through `Fw::Success::SUCCESS` and `Fw::Success::FAILURE` statuses per the [Framer Status Protocol](../../../docs/reference/communication-adapter-interface.md#framer-status-protocol), including the initial start-up SUCCESS and any recovery SUCCESS following a FAILURE.   | Unit-Test    |


## Design

![Component Block Diagram](./img/diagram.svg)

`Svc.ComAggregator` implements `Svc.Framer`.  Additionally, it has a `Svc.Sched` timeout port enabling timeout to be driven via a rate group.

### Threading Model

`Svc.ComAggregator` is an active component whose input ports are all `sync`: port handlers run on the caller's thread and do no work beyond sending a signal to the `AggregationMachine` state machine instance. State machine signals are internally enqueued on the component's message queue, so all state machine actions and guards execute serially on the component's own thread. This keeps callers non-blocking while ensuring the aggregation state (frame buffer, held buffer, last context) is only touched from one thread. The only state shared across threads is the buffer ownership flag, which is an atomic exchanged in `dataReturnIn_handler` (caller thread) and `doSend` (component thread).