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0001 \section{Pixel Data Format}\label{sec:Pixel}
0002 %% Danek Kotlinski, first version from 25/5/05
0003 The pixel Front End Driver (FED) readout board will read
0004 data from 36 input links, build events, and send the event
0005 packets through the S-link to the DAQ.
0006 During the event building it has to reconstruct pixel
0007 addresses from the 6-level analog signals. This procedure
0008 requires a set of pre-programmed threshold levels.
0009
0010 Each FED will send to the DAQ a data packet starting with the standard
0011 packet header and ending with the standard packet trailer.
0012 The header includes a bit field identifying uniquely the FED.
0013 Between the header and the trailer there will be a variable number of
0014 32-bit data words, with one pixel stored per word.
0015 The format of the 32-bit word is:
0016 \begin{itemize}
0017 \item 6-bit Link id, defines the input link to the FED (0-35);
0018 \item 5-bit ROC id, defines the ROC within one link (0-23);
0019 \item 5-bit Double-Column id, define the double column within
0020 on ROC (0-25);
0021 \item 8-bit Pixel id, define the pixel address within on
0022 Double-Column (0-179);
0023 \item 8-bit ADC value, the signal amplitude, extracted from a
0024 10-bit ADC.
0025 \end{itemize}
0026 Table~\ref{tab:pix1} summarizes the pixel format.
0027
0028 Note that in our data format the source id (FED number) is not
0029 included. We depend on the source id included in the DAQ S-link
0030 header. This header should be available in the code which will
0031 transform the raw data format to the format used in the reconstruction
0032 code.
0033
0034 % Pixel data format
0035 \begin{table}[htb]
0036 \caption{Pixel readout format}\label{tab:pix1}
0037 \begin{bittabular}{32}
0038 & \bitNumFourByte
0039 \bitline{pixel&\field{6}{LINK-ID}&\field{5}{ROC-ID}&\field{5}{DCOL-ID}&
0040 \field{8}{PIX-ID} & \field{8}{ADC}}
0041 \bitline{ & 5&4&3&2&1&0 & 4&3&2&1&0 & 4&3&2&1&0 & 7&6&5&4&3&2&1&0 &
0042 7&6&5&4&3&2&1&0}
0043 %% & \bitNumFourByte
0044 \end{bittabular}
0045 \end{table}
0046
0047 Based on this format the FED data volume in bytes is calculated as
0048 4 * (3 + number-of-pixels).
0049 The pixel barrel readout has been arranged in such a way to
0050 approximately fit the requirement of 2.0~kB per FED at high luminosity.
0051 For the low luminosity pp collisions, the pixel data volume for
0052 the barrel FEDs will be around 0.6~kB per event.
0053 The difference between various FEDs should be around 10\%.
0054 For the pixel endcaps the data volume per FED will be smaller,
0055 about 1.8(0.55) kB per event at high(low) luminosity.
0056
0057 When reading data over VME an alternative "raw" data format
0058 is foreseen in addition to the standard one. This format
0059 will be only used during the level calibration procedure
0060 performed in a XDAQ client application and will never be used
0061 in ORCA.
0062
0063 %%% Local Variables:
0064 %%% mode: latex
0065 %%% TeX-master: "DataFormats"
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