Payload Encoder

The EncoderPayload library is building raw data buffer for data payloads. How those payloads are then ordered exactly in memory / on file is not the library business. This choice has been made to minimize the dependency of the Encoder code on the RawDataHeader itself. To that end the Encoder is producing data buffers consisting of (header,payload) blocks, where header is not a RDH but a simpler (and non versioned) struct. Contrary to (RDH,payload) blocks, the payload can be any size (while in RDH the size is limited to 65536 bytes). The part of the detector that a payload block references is identified through the solarId field.

createPayloadEncoder

To creation of a MCH PayloadEncoder is handled through a template function. For instance, to create an Encoder that builds raw data in BareFormat and ChargeSumMode, use :

#include "MCHRawEncoderPayload/PayloadEncoder.h"
 
auto encoder = o2::mch::raw::createPayloadEncoder<BareFormat,ChargeSumMode>();

Then for each interaction record (aka orbit,bunch crossing pair) you tell the encoder to start a new Heartbeat Frame, fill it with all the data of the channels and then extract the memory buffer.

vector<uint8_t> buffer;
for ( loop over interactions )
  encoder->startHeartbeatFrame(orbit,bc);
  for ( loop over digits ) {
    DsElecId elecId = ... // get electronic dual sampa id from digit
      int sampaChannelId = ... // get sampa channel id from digits
      vector<SampaClusters> clusters = ... // create sampa clusters from digits
      encoder->addChannelData(elecId,sampaChannelId,clusters);
  }
encoder->moveToBuffer(buffer);
}

At this stage the buffer contains (header,payload) blocks for all the interactions you looped over. But it is not yet a valid raw data, as it lacks RDHs (and has mch-specific headers instead).

The conversion from payload buffers to RDH-base buffers is basically done using the o2::mch::raw::PayloadPaginator class (internally using the o2::raw::RawFileWriter framework class). A typical usage example is in the digit2raw program.

Advanced usage

The createPayloadEncoder actually takes one parameter, a function that converts a solarId into a FeeLinkId (aka a Solar2FeeLinkMapper). The default value should fit the electronic mapping of the actual detector and thus should be fine in most cases. For special use cases a different mapper can be provided though.