On Sat, 4 Jul 2009 00:03:19 +0200 (MET DST) j...@uriah.heep.sax.de (Joerg Wunsch) wrote:
> Apart from that, JTAG is pretty fast. I remember that you told me (a year ago maybe..) not to expect JTAG to be very fast because its protocol included many delays which slowed things down. Hence why I was a little surprised, but pleased, to see that it is fast enough to my taste despite these delays. > On the plus side, the JTAG programming speed is completely independent of the > target's clock > speed (the target is not even required to have a working clock at > all), as JTAG has its own clock. Yes, that's one of the reasons I fancied JTAG.. because if you get the clock fuses wrong, it's easy to correct them via JTAG... but not so easy/convenient with ISP.. been there done that ! ;-) That said, ISP does have a clock signal too ! So fundamentally, I don't understand why ISP requires the target to also have its clock working ? Nevermind... > (Only when debugging through JTAG, > the JTAG clock must (again) not exceed fCPU/4.) Oops, didn't know that, thanks for the info... > Even though the ISP implementation that is embedded into the JTAG ICE > and AVR Dragon is basically the same as an AVRISPmkII, for some reason > it cannot reach the ISP speed of the AVRISPmkII. My guess is this is > due to wrapping the AVRISPmkII protocol within the JTAG ICE mkII > protocol, causing additional overhead. Hmm, I don't think I will leave my Dragon to go back to a pure ISP programmer. Tonight JTAG has proved to be fast enough to my taste, and most of all it has so many advantages/features over ISP, that I would have to be dumb to go back to ISP I think ! ;-) I think I will rework my PCB to suit ! :-) -- Vince, happy bunny _______________________________________________ AVR-chat mailing list AVR-chat@nongnu.org http://lists.nongnu.org/mailman/listinfo/avr-chat
