# DigitalDownConverter — Interfaces

## Input Stream

The pipeline consumes one SPEAD2 multicast stream in `MPIFR_EDD_Packetizer:2` format.
The stream description is provided via the `input_data_streams` configuration key.

| Field | Value |
|---|---|
| Format | `MPIFR_EDD_Packetizer:2` |
| Default sample rate | 4 Gsps |
| Default bit depth | 8 bit |
| Default samples per heap | 4096 |
| SPEAD2 item: timestep | id 5632 |
| SPEAD2 item: polarization | id 5633 |
| SPEAD2 item: payload | id 5634 |

## Output Streams

The pipeline publishes one SPEAD2 multicast stream per output channel in
`DigitalDownConverter:1` format.

```{include} ../generated/ddc_processor/streams.md
```

### Channel Naming Convention

Output stream keys in `output_data_streams` follow the pattern:

```
polarization_<pol>_<channel>_lower
polarization_<pol>_<channel>_upper
```

where `<pol>` is the polarisation index and `<channel>` corresponds to the LO index in
`f_lo`. Center frequencies are computed as `f_lo[i] ± output_samplerate/4`.

## KATCP Interface

The pipeline exposes a standard EDD KATCP server. Key requests:

| Request | Description |
|---|---|
| `?configure <json>` | Load a new configuration |
| `?capture-start` | Begin data capture |
| `?capture-stop` | Stop data capture |
| `?deconfigure` | Release resources |
| `?sensor-list` | List available sensors |
| `?sensor-value <name>` | Query a sensor |