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1)I did an experiment and compiled OpenBTS with clang yesterday, which immediately highlighted two potential bugs in the Transceiver52 code. I'm not sure they are indeed bugs and not the intended behavior, but they look very much like that. The first one is below and the second one is in the following mail. GSM::Time() arguments are defined like #define USB_LATENCY_INTRVL (10,0), which means that they are expanded into GSM::Time((10,0)). This expression is a GSM::Time() with a single parameter where (10,0) return value of the last argument, 0 in this case. I.e. GSM::Time((10,0)) is equivalent to GSM::Time(0). I think this was not the intention. 2) Printing \n after every complex number breaks output when you want to print it in a single line, e.g. in many debug output. I do not claim any copyright over this change, as it's very basic. Looking forward to see it merged into mainline. git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@4515 19bc5d8c-e614-43d4-8b26-e1612bc8e597
The Transceiver The transceiver consists of three modules: --- transceiver --- radioInterface --- USRPDevice The USRPDevice module is basically a driver that reads/writes packets to a USRP with two RFX900 daughterboards, board A is the Tx chain and board B is the Rx chain. The radioInterface module is basically an interface b/w the transceiver and the USRP. It operates the basestation clock based upon the sample count of received USRP samples. Packets from the USRP are queued and segmented into GSM bursts that are passed up to the transceiver; bursts from the transceiver are passed down to the USRP. The transceiver basically operates "layer 0" of the GSM stack, performing the modulation, detection, and demodulation of GSM bursts. It communicates with the GSM stack via three UDP sockets, one socket for data, one for control messages, and one socket to pass clocking information. The transceiver contains a priority queue to sort to-be-transmitted bursts, and a filler table to fill in timeslots that do not have bursts in the priority queue. The transceiver tries to stay ahead of the basestation clock, adapting its latency when underruns are reported by the radioInterface/USRP. Received bursts (from the radioInterface) pass through a simple energy detector, a RACH or midamble correlator, and a DFE-based demodulator. NOTE: There's a SWLOOPBACK #define statement, where the USRP is replaced with a memory buffer. In this mode, data written to the USRP is actually stored in a buffer, and read commands to the USRP simply pull data from this buffer. This was very useful in early testing, and still may be useful in testing basic Transceiver and radioInterface functionality.