Re: [avr-chat] Dragon: mega slow at dumping Flash, normal ?

[Vincent Trouilliez]

On Sat,  4 Jul 2009 00:03:19 +0200 (MET DST)
address@hidden (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