On Sun, Oct 20, 2013 at 8:55 PM, Paul Sokolovsky <[email protected]> wrote:
> Hello,
>
> On Sun, 20 Oct 2013 20:21:19 +0200
> Andreas Fritiofson <[email protected]> wrote:
>
> []
>
> > > > Who would use ATMega if it costs _more_ than modern controllers
> > > > but allows to do much, much _less_?
> > >
> > > Probably those who have paid for it already. Also those, who keep
> > > using awfully expensive FT232* stuff...
> > >
> > >
> > I don't get what you mean with "awfully expensive"... A suitable FTDI
> > chip is about the same price (+/- 50%) compared to a ATMega series
> > AVR chip.
>
> Well, I mean just that - some dumb USB-UART/bitbang converter costs
> like a whole general-purpose MCU (while there're other USB-UART
> converters which cost much less).
>
Yes, but it doesn't matter how general-purpose your MCU is if you're going
to use it as a JTAG adapter. The FTDI chip already IS a JTAG adapter, no
firmware development needed, the support is already in place in OpenOCD,
just plug'n'play, and it does the job much much better than the 8-bit MCU
will.
> And a complete development module with a FT232H is the same
> > price as an Arduino Micro. And by the same reasoning, why would you
> > bother with making a lousy JTAG adapter out of an AVR if you already
> > are "using awfully expensive FT232* stuff"?
>
> The original talk was of using something else besides that, and yet
> there's whole bunch of FT-based JTAG adapters, and I'm not sure they're
> going to be displaced soon - because they work, and work kinda well.
> But we digress here. My aim is not to compare different hardware (I
> don't challenge that some is more suitable for JTAG than other), but
> to support it all, without placing arguably arbitrary cutovers.
>
>
Ok, we can skip the FTDI-vs-MCU discussion. It's just that, for me, FTDI
based stuff is what I "have lying around" if I wanted to make my own JTAG
adapter. I don't have any Arduino boards. Most "LCB" I have already come
with embedded debug adapters. And many of those can be reflashed as
BlackMagicProbe or CMSIS-DAP interfaces if I should want to.
What I don't understand from your series of mails was the rationale for
creating yet another (low-performance) protocol for host-to-JTAG. And the
rationale for actually using it.
/Andreas
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