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    User name R. Michaels

    Log entry time 14:13:39 on February 26, 2006

    Entry number 164034

    Followups:

    keyword=CAEN 767 problem investigation

    I investigated the problem with the CAEN 767 decoding.
    There are several problems, though luckily it did not corrupt
    other crates. I wrote a detailed diagnosis in the analysis
    logbook : HERE

    Briefly, one problem is that there are many "bad chip" errors
    but this flag is ignored -- hence analysis workers are ignorant
    of how many errors except that they don't see data. Second
    problem is that because of the bad chip flags the decoder gets
    "lost" in this crate and ends up checking the high rate scaler
    clock, and since this sometimes has higher-order bits it thinks
    it might be a TDC, but the data are inconsistent so it rejects
    it (indeed it rejects the whole event !!). Third problem is
    the decoding is very inefficient; something to keep in mind
    for the future of VME is that we need clear header info for
    each slot, denoting the slot# and number of hits.

    I've explained techy details in the analysis logbook, but since we
    are presumably going to replace 767 with Fastbus anyway (because
    of the huge bad-chip rate) it is academic. I think the decoding
    for Fastbus will be faster, and we know it is quite reliable.

    A copy of this log entry has been emailed to: bogdanw@jlab.org,brads@jlab.org