Hi Bruce, Yes - at this point an external processor is not a real option.
Are you aware of open source code that I could try out? In hind sight, I should've put a microprocessor core onto the FPGA to do all the management kind of tasks. Regards, Stephan. No need to use an external processor just implement a processor within the FPGA. VHDL code for suitable processors is readily available. Bruce Bruce 2008/11/19 Bruce Griffiths <[EMAIL PROTECTED]> > Tom Van Baak wrote: > > Stephan, > > > > Ah, it's not a stupid question -- I think all of us who have written > > code to interface with GPS receivers have had to deal with this. > > > > Some GPS protocols use escape characters, but the Oncore > > binary protocol doesn't. There are five clues to robustly parsing > > a complete message: > > > > 1) starts with @@ > > 2) ends with <cr><lf> > > 3) message length is known, based on message header > > 4) valid checksum > > 5) there may be a pause between sentences > > > > You can use all of these clues to "sync" to a serial data stream > > and accurately determine the start of the next message. > > > > As you already observed, just looking for @@ or <cr><lf> is > > not sufficient. Checking for <cr><lf>@@ is better, but still not > > perfect. To do it right you also need to include message length > > and checksum into the calculation. The length is knowable by > > looking at the message type in the header as it arrives. > > > > If you use a millisecond-level serial timeout that can help even > > more (since if the first two bytes after a pause are @@ you > > know it is a message start, not 16-bits of 0x4040 embedded > > binary data). There is a timing gap between some, but not all > > messages, so use this technique with care. You can also use > > the 1PPS pulse as a start of message hint. > > > > True, a robust solution is not FPGA-friendly, but probably not > > impossible, either. If you can't solve it, consider using a $1 > > microcontroller (where this sort of message handling is trivial) > > between the receiver and your FPGA which would parse, edit, > > or reformat the messages to the FPGA's liking. > > > > /tvb > > > > > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
