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Re: [c6x] Re: [c55x] CC and JTAG with other devices in the scan chain

Started by Jerry \Signum\ June 5, 2003
Jeff,

If you are having problems with noise on long JTAG chains,
try to buffer the JTAG lines. I have seen boards with 16 C6000
DSPs on a single chain that worked just fine.
I guess the trick may be in keeping the JTAG lines well laid out on the PCB.

If it is too late for adding buffers, you can use an emulator that buffers the
JTAG signals right at the JTAG target header, before they go into
the several inches of the emulator cable.
I believe Signum is the only company that does it -see
www.signum.com/jtagjet.htm
It also lets you change the JTAG clock in steps from 1 kHz to 30 MHz
with software.
You can send us your board and we will test it at the desired JTAG clock
at no charge.

Jerry Lewandowski
Signum Systems Corp.
www.signum.com ----- Original Message -----
From: "Jeff Brower" <>
To: "Gagan Singh" <>
Cc: <>; <>; <>
Sent: Wednesday, June 04, 2003 8:36 AM
Subject: [c6x] Re: [c55x] CC and JTAG with other devices in the scan chain > Gagan-
>
> > The JTAG clock freq control is provided
> > in the POD only. It is for the manufacure to give
> > some kind of interface to do so. In my case we did
> > use flexds emulators. They did provided control to
> > change JTAG clock by jumper settings in the POD
> > itself.
>
> Ok, score one for Flexds emulators, that is an excellent feature. I think I
will
> e-mail the Mike and Danny at Spectrum Digital and see what is their suggestion
on how
> to do it with their units.
>
> Jeff Brower
> system engineer
> Signalogic > > Plus u have to specify the same in ur config file
> > placed mostly in ..\ti\cc\bin
> >
> > Regards
> > Gagan



Jerry-

> If you are having problems with noise on long JTAG chains,
> try to buffer the JTAG lines. I have seen boards with 16 C6000
> DSPs on a single chain that worked just fine.

We do that as much as possible, but in many cases we don't have room for
buffers, or
at least more than one set. The boards are typically small and dense, 10 layer
to
16-layer, two examples are shown at:

http://www.signalogic.com/sigc67xx_sodimm.htm

http://www.signalogic.com/sigc5441_sar_ptmc.htm

The first one gave us a lot of JTAG trouble because we needed a bus switch to
select
between CPLD JTAG and DSP JTAG chain, so we sacrificed the buffer, relying on
the
buffer on the base board. Bad move. The buffer is back on now, wedged in there
somehow.

> I guess the trick may be in keeping the JTAG lines well laid out on the PCB.

Yep we always pay very careful attention to that. We also leave zero-ohm Rs to
allow
the chain to be shortened at several points. But even an inch or so on a
gnd-protected clock trace layer can still be enough to cause problems with TCK,
it's
just very sensitive to any acquired noise. I would say this signal is not a
favorite
of our engineers.

> If it is too late for adding buffers, you can use an emulator that buffers the
> JTAG signals right at the JTAG target header, before they go into
> the several inches of the emulator cable.
> I believe Signum is the only company that does it -see
www.signum.com/jtagjet.htm
> It also lets you change the JTAG clock in steps from 1 kHz to 30 MHz
> with software.

With software? Those are very good features.

> You can send us your board and we will test it at the desired JTAG clock
> at no charge.

Yes I will keep this in mind! Thanks Jerry.

Jeff Brower
system engineer
Signalogic

> ----- Original Message -----
> From: "Jeff Brower" <>
> To: "Gagan Singh" <>
> Cc: <>; <>; <>
> Sent: Wednesday, June 04, 2003 8:36 AM
> Subject: [c6x] Re: [c55x] CC and JTAG with other devices in the scan chain
>
> > Gagan-
> >
> > > The JTAG clock freq control is provided
> > > in the POD only. It is for the manufacure to give
> > > some kind of interface to do so. In my case we did
> > > use flexds emulators. They did provided control to
> > > change JTAG clock by jumper settings in the POD
> > > itself.
> >
> > Ok, score one for Flexds emulators, that is an excellent feature. I think I
will
> > e-mail the Mike and Danny at Spectrum Digital and see what is their
suggestion on how
> > to do it with their units.
> >
> > Jeff Brower
> > system engineer
> > Signalogic
> >
> >
> > > Plus u have to specify the same in ur config file
> > > placed mostly in ..\ti\cc\bin
> > >
> > > Regards
> > > Gagan