.1.4, DDU control FPGA The DDU control is for control and readout the four external FIFos, as well as status and data transmission. reporting, error checking and recording, for data to arrive at After L1A, the DDU control FPGA waits the event. The 36 the external FIFos and then begins to process creating a and bit wide FIFo data are read at double data rate, for csc data, word structure in the FPGA. of these bits, 64 are the other eight contain status and control signals each FlFo FPGA initially checks the first word from signals, to verify the L1A counter synchronicity, check for error data and which cscs have data Flagged in the am are registered and the event information from FlFos without csc data is logged and discarded Full event data processing follows for those FlFos containing CSC data: the data is continuously read from the external FIFO until the end boundary is detected. At this point the Control FPGA checks the end boundary word for additional error signals from the Input FPGA, then switches to the next FlFo containing event data and continues processing. Before transmitting event data, the Control FPGA creates header words to describe the event record The trailer words are generated at the end of the event record which contain processing and status summaries. The DDU will send at least the header and trailer words for every L1A, even if there is no csc data to read out. During event processing, the Control FPGA performs over 70 consistency checks on each event. If there is a single-occurrence error, such as a CRC failure, then the event is flagged as"bad" in the DDU trailer and normal data processing continues unin- terrupted. Any errors that are detected get recorded in VMEaccessible registers and are included in a status word that is transmitted at the each event. When a serious error is end of the can request a CMS detector reset directly from the DDU to the CMS TTS system, or by using a VME interrupt to inform the crate controller, and then the controller can initiate a CMS detector reset request. The Control FPGA transmits data to the DCC through two pairs of dedicated high-speed serial connection on the FED Crate custom backplane. Additionally, the data are also sent to an external FIFO for eventual transmission to the CSC local DAQfarm. Data are stored in that FIFO until there are enough to build a Gigabit Ethernet(GbE) data packet. At that point the data in the FIFo gets read back into the FPGA, where the GbE packet structure is generated and the data are serialized by a MGT module for transmission to the CSC local DAQ farm. A GbE pre-scale register on DDU is available to specify the fraction of events(1/1 to 1/8192) that are transferred to the CSC local DAQ farm. Additionally, the FIFO overflow protection will automatically limit the data rate to the local DAQ farm. The DDU Control FPGA monitors the status of the four external FIFO pairs. When any of them are three quarters full, the DDU issues a Warning signal to the CMS TTS, which requests a L1A rate reduction until that FIFO is nearly empty. However, if a FIFO has space left for only one single large event, the DDU issues a Busy signal to the CMS TTS, which request a stop of the L1As and the DAQMBs are signaled to stop sending data. Once set, the Busy signal remains asserted until the FIFO is Biểu tượng cảm xúc heart quarters full.
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