I just wonder if I do not have one flipflop after the MUX and before the output buffer, it follow the standard or not? And does it affect to output TDO (fanout/delay/anything)?
If any of your chains sync to the neg edge then you must sync all of them before muxing them out to the TDO pad. If all of your chains are pos edged synced then you can add a neg edge flop
between the mux and the tdo pad.
If your tdo is going to an internal daisy chain then you can simply pass on the pos edge synced signals. Synthesys will handle the hold time issues
You can send a neg edged synced TDO to an internal daisy chain but it cuts your max clock rate in half.
John Eaton