Figure 1: Schematic data flow from the Hit Finding point of view
After digitization of the analogue raw data, they are fed to the PowerPC memory via the PCI bus. After that the board is ready to signal L3 Keep Acknowledge to the H1 trigger system. If the Hits & Cluster readout mode is selected the main SiDAQ task then calls the Hit Finding routine. Its task is then to read data from the specified raw data buffer, find the hits and write them, correctly formatted, to the specified hit data buffer.
It must be ensured that there are NEVER NEVER more than 32 kBytes written to the Hit Buffer Area by the Hit Finding routine.
The Hit Finding includes the read access of the Pedestal and Sigma memory areas. Write access to these areas is part only of the Constant Update routine.
If the Hit Finding returned successfully, the data are then picked up by the VMEtaxi. The Taxi also is responsible for adding the BOS bank headers to the data.
In case Raw data readout mode is selected, the taxi reads directly from the raw data buffer, i.e. the Hit Finding routine is not called.
Having collected the data of one buffer the taxi flags this buffer as free to be filled again.