SCT Bytestream Hacking Bruce Gallop RAL High mu upgrade - 16 th May 2012

ROD Dataflow 96*40Mbs links into ROD – 3.84Gbps 32*40Mbs S-Link out of ROD – 1.28Gbs It doesn’t fit!! ABCD format has redundancy – Fixed header, trailer – BC and L1ID should be the same on all links – Three time bins -> 4 bits per hit

SCT Bytestream The ROD formatter converts data from ABCD bitstream to “bytestream” Sent to ROS over S-link Becomes a ROD event fragment Wrapped up by ROS and put into the ATLAS event Interpreted offline by bytestream decoder

ROD Event Fragment 9 32-bit words header: – Header, size, version, RODID, run, L1, BC, ttype, event type DATA (n*16-bit words) – Link header (present if hits on link) – Hit words – Link trailer (present if errors in trailer) 5 32-bit words trailer – 2*status, size, nwords, format

Data Words Link header “following words are from this link” Clusters of hits (within a chip) stored in sequence – Expanded: Start of cluster 1FFFFCCCCCCC0DDD 1 hit cluster 1xxxxxxx0xxx1DDD 2 hit cluster 1xxxxxxx1DDD1DDD 3 hits = S + 2, 4 hits = S etc – Condensed: One hit 1FFFFCCCCCCCxfx0 Two hit 1FFFFCCCCCCCsfx1 3 hits = 2 + 1, 4 hits = etc Trailer “there were errors in the trailer”

Unused Bits ROD fragment header/trailer – But only once per fragment In data words (x on previous page) Condensed mode assumes 1 or 2 hit clusters – 3 or more hits repeats the chip and channel Error flags – Link header/trailer

New Format Strawman Keep fragment header/trailer One of many possibilities Based on bits – Link header 8 bits (0) + 7 bits – Cluster 12 + n*2 bits (1) + 11 (chip+channel) + 2 bits per hit – No error bits (still have fragment trailer) Simulation suggests (qv Susumu’s talk) – ~15% improvement 44-58

Variations Drop link header for “no hits on this link” Cluster: chip+channel + 4bits n-hits (16bits) – cluster of 16 or more uses more words Restore some bits for errors Fragment H/T based on ATLAS format 3 – Can be substantially reduced in 4 – L1, BC absolutely required, check others

Why Not? ROD is stable – Last format change was a bit in the link header to signify a disabled link Lots of software to update – Histogramming engine in ROD DSP – Byte stream converter in offline – ROS monitoring code Possibly lose details of errors Needs lots of testing

Time estimates ROD FPGAs – Formatter converts bitstream to stream of words – EFB collects link fragments and checks some errors – Router transfers data to SLink 16-bit words: – Changes mostly in formatter, also handling of errors Couple of months for firmware Testing a few months (schedule permitting) Software similar Irregular words: – Changes to other parts of datapath Affects Pixel too (formatter only detector specific code) Estimate at least double time for implementation

Conclusions There is room for improvement in the bytestream mainly due to the packing of larger clusters Suggestion from simulation is a gain of 15% with a naive scheme Quite a bit of disruption to different areas – Significant ROD firmware update – Different software

ABCD format Header – Counters – LLLLBBBBBBBB Hits – 01CCCCccccccc(0xxx)* No hit – 001 Trailer –

Hit data Header: 001ptlbKdMMMMMMM Trailer: 010zhvxxxxxxxxxx 1 hit condensed 1FFFFCCCCCCCxfx0 2 hits condensed 1FFFFCCCCCCCsfx1 1st hit cluster expanded 1FFFFCCCCCCC0DDD 1 hit cluster expanded 1xxxxxxx0xxx1DDD 2 hit cluster expanded 1xxxxxxx1DDD1DDD Flagged error 000xxxxxxFFFFEEE Raw data 011nnnxxWWWWWWWW