1 DAQ.IHEP Beijing, CAS.CHINA mail to: The Readout In BESIII DAQ Framework The BESIII DAQ system consists of the readout subsystem, the online control and monitoring system, the calibration system and other support/service systems. BESIII DAQ Frame The Structure of readout subsystem The Implementation of DAQ readout software -The tasks of DAQ system. Configuration Database Event Data Readout from FEE Event Building Event Filtering Event Recording to Persistent Media Run Control System Monitoring (event, histogram display...) Message Reporting -The bottom of the DAQ frame is readout subsystem. (consult figure 1) The Functions of readout subsystem -Be made up of several readout branches, and each branch has several VME crates. -The composing of each VME crate. ■ No more than 16 FEE readout modules. ■ FEE control module. ■ One embedded single board computer MVME5100, as system controller. ■ MVME5100 runs vxworks5.4 real time operating system. (consult figure 1) -Receive commands from online control system and control data readout. -Receive configuration information from online, configure and control FEE modules. -Collect data from FEE readout modules in CBLT (Chained Block Transfer) method. -Pack collected data for upload. -Upload packed data to readout PC of online system. -Report error and system status to online. -The read out subsystem use a state machine to control running. · The state machine makes readout subsystem get command from online system and carry out corresponding actions. Figure 1 Figure 2 Figure 3

2 DAQ.IHEP Beijing, CAS.CHINA mail to: The Readout In BESIII DAQ Framework Error and Status Report of readout system The Data Readout process · 12 types of commands and 9 states are defined. · When received command, the state of state machine transit from one to another, and corresponding operations must be accomplished. After carry out the operations, an acknowledgement is send to online software to notify this transition success or not. -The interface between read out subsystem and online software of DAQ · Three socket channels are built for communication between the two system. √socket 1: receive command from and send acknowledgements to online. The configuration information used to configure FEE modules also download through here. √socket 2: report the system error and status information to online software. √socket 3: send valid data to online system. -The interface between data readout system and FEE. · Readout subsystem communicates with FEE module via VME bus. · Two types of information are exchanged. √type 1:information configure and control the FEE modules. √type 2:event data that read out from FEE modules. Note: Figure 4 shows the data flow of readout subsystem and its interface with other correlative systems. -Three main parallel tasks are spawn for data read out process. -Semaphore and message queue are used for communication and synchronization between multi tasks. -Multi level Ring buffers are also employed to improve system parallelization and stability. (consult the figures 4 and 5) -A compatible structure is defined for reporting system error and status. -Error report defines error level, error type and slot information for error FEE modules in the structure. -System status is reported periodically, including the memory using, CPU load, and net speed information. -Sometimes interrupt information is also reported as system status. Conclusion -The DAQ of BESIII has been tested partly. Result shows that readout subsystem can work well with FEE subsystem and online software. Result also says the system can reach designed performance. Figure 4 Figure 5