The HADES trigger and readout board network (TrbNet)

HADES is a running hadron and di-electron spectrometer installed at GSI, Germany. Currently, the HADES data and trigger system is being upgraded. The main aim is an increase in the event rate capabilities by a factor of up to 20 to reach 100 kHz in light systems and 20 kHz in heavy ion reactions. The datarate will be in the order of 400 MByte/s in peak. In this context, the complete readout system has been exchanged to use optical communication. In this contribution we present a general-purpose real-time network protocol that has been developed based on our requirements. These include strong timing constraints with latencies less than 5 μs for endpoint-to-endpoint communication including up to 10 intermediate hubs in a star-like network setup. In HADES, this network connects over 500 FPGAs distributed over the whole detector. Monitoring and slow control features as well as readout and trigger transportation were joined in a single network protocol. Hence, channel multiplexing with inherent arbitration by priority is implemented. Typically, switching from one channel to another takes less than 100 ns. For slow control and monitoring, a dedicated channel provides a data bus with a virtual address space spanning the whole network. The configuration is highly flexible and thus adaptable to different experimental setups and hardware. Therefore, the network can also be used in any other experiment of the upcoming FAIR facility.