100m JTAG cable

This might be slightly OT for an FPGA group, but maybe someone has run
into a similar problem before:

I'd like to connect my FPGA, via JTAG, to my PC, 100m away.  Due to a
hazardous environment, putting the PC any closer isn't feasible

I'm using a Xilinx parallel cable III, which I extended with RS485
drivers to get to required distance, before converting back to TTL to
drive the original cable.

Currently, Impact (correctly) finds the correct number of devices on
the JTAG chain on two different boards, but identification fails.

A bit of exploration with a scope shows data flowing pretty much as
expected, with a clean wave arriving at the board.  Another, rather
worrying, aspect is that the transmission delay through the systems is
about 800ns - rather a lot on a 200kHz communication system.

Does someone perhaps know whether impact will get upset with the delay?
 Is there away around it?  (As far as I can see, my cable doesn't
respond to the speed setting in Impact)

Any suggestions would be appreciated.

johannes

http://www.ee.sun.ac.za/~jvdh

jvdh wrote
> This might be slightly OT for an FPGA group, but maybe someone has run
> into a similar problem before:
>
> I'd like to connect my FPGA, via JTAG, to my PC, 100m away.  Due to a
> hazardous environment, putting the PC any closer isn't feasible
>
> I'm using a Xilinx parallel cable III, which I extended with RS485
> drivers to get to required distance, before converting back to TTL to
> drive the original cable.

Could you switch to using a USB cable, extended via off-the-shelf fiber 
optic USB extenders?

I like the (off the shelf) simplicity of your suggeston :)

The way I see it, the main options would be changing the medium (esp to
fibre), or slowing the comms down - the later would probably be
preferable from a cost point of view...

But I'm first trying to confirm that it definitely is the transmission
delay that's messing me around.

Thanks!

Tim wrote:
> jvdh wrote
> > This might be slightly OT for an FPGA group, but maybe someone has run
> > into a similar problem before:
> >
> > I'd like to connect my FPGA, via JTAG, to my PC, 100m away.  Due to a
> > hazardous environment, putting the PC any closer isn't feasible
> >
> > I'm using a Xilinx parallel cable III, which I extended with RS485
> > drivers to get to required distance, before converting back to TTL to
> > drive the original cable.
>
> Could you switch to using a USB cable, extended via off-the-shelf fiber
> optic USB extenders?

jvdh <johannes.vanderhorst@gmail.com> wrote:
> I like the (off the shelf) simplicity of your suggeston :)

> The way I see it, the main options would be changing the medium (esp to
> fibre), or slowing the comms down - the later would probably be
> preferable from a cost point of view...

> But I'm first trying to confirm that it definitely is the transmission
> delay that's messing me around.

Isn't there an option to set the JTAG CLK speed in impact? 

Another option beside the USB Extender is to convert the levels to a
RS422/485 signal and use a twisted pair cable.
-- 
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

jvdh wrote:
> This might be slightly OT for an FPGA group, but maybe someone has run
> into a similar problem before:
> 
> I'd like to connect my FPGA, via JTAG, to my PC, 100m away.  Due to a
> hazardous environment, putting the PC any closer isn't feasible

Can you clarify hazardous - is this electrically noisy, or soemthing 
else. If it is electrically noisy, RS485 may not be enough.

> 
> I'm using a Xilinx parallel cable III, which I extended with RS485
> drivers to get to required distance, before converting back to TTL to
> drive the original cable.
> 
> Currently, Impact (correctly) finds the correct number of devices on
> the JTAG chain on two different boards, but identification fails.
> 
> A bit of exploration with a scope shows data flowing pretty much as
> expected, with a clean wave arriving at the board.  Another, rather
> worrying, aspect is that the transmission delay through the systems is
> about 800ns - rather a lot on a 200kHz communication system.
> 
> Does someone perhaps know whether impact will get upset with the delay?
>  Is there away around it?  (As far as I can see, my cable doesn't
> respond to the speed setting in Impact)
> 
> Any suggestions would be appreciated.
> 
> johannes
> 
> http://www.ee.sun.ac.za/~jvdh

You could create a deliberate bench-delay, ( schmitt buffers and RC 
elements ) and see if that is ok in your lab. It should also let you 
test various download software's delay tolerances.

- that helps isolate delay effects from other noise effects.

You may need an isolated link system, RS485 has finite common mode 
limits - but isolation will add to your delay budget...

I think analog devices have some high speed isolators ?

-jg

Jim Granville <no.spam@designtools.co.nz> wrote:
...

> You may need an isolated link system, RS485 has finite common mode 
> limits - but isolation will add to your delay budget...

> I think analog devices have some high speed isolators ?

I use the ADUM1401 for that task, in connection with SPI transfers. Jtag
shouldn't be too different. 

-- 
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

Uwe:

> Isn't there an option to set the JTAG CLK speed in impact?
The speed setting in impact apparently doesn't apply to my Parallel
Cable 3.

> Another option beside the USB Extender is to convert the levels to a
> RS422/485 signal and use a twisted pair cable.

This is exactly what i'm doing, with an RS485 driver and receiver on
each end of my cable. I'm getting 230kbps on the system for serial
communication:), but I think my transmission delay is too large for
Impact to be happy.  I measured the duration of a clock pulse to be as
little as 1us - with a delay of 800ns, the reading of data fails.

Jim:
Hazardous as in high energy particles, especially protons and neutrons.
 The board will be used to test radiation tolerance techniques, but
background radiation is too high to put a PC nearby for control. (and
want to use it afterwards:)  It is inside a faraday cage, so even very
high speed wireless options are also out.

I'm using a differential line pair for every input signal - the R485 is
only used as a repeater and receiver pair, with no other 485 protocol
on top of it.

Right now I'm looking into the open source options, hoping I can do
(slower) readback with openwince-jtag.

thank you!

jvdh (johannes.vanderhorst@gmail.com) wrote:
: This might be slightly OT for an FPGA group, but maybe someone has run
: into a similar problem before:

: I'd like to connect my FPGA, via JTAG, to my PC, 100m away.  Due to a
: hazardous environment, putting the PC any closer isn't feasible

One approach, nicely agnostic to the deviecs and manifactuers etc, would 
be to extend the physical JTAG signals with fibre transcievers.  I guess 
that doesn't work for Vref directly... :-)

Assuming fibres aren't killed by the radiation...

jvdh <johannes.vanderhorst@gmail.com> wrote:
> Uwe:

> > Isn't there an option to set the JTAG CLK speed in impact?
> The speed setting in impact apparently doesn't apply to my Parallel
> Cable 3.

> > Another option beside the USB Extender is to convert the levels to a
> > RS422/485 signal and use a twisted pair cable.

The FTDI FT2232 happily generates serial protocols. I have a modified version
of Andrew Rogers's xc3sprog thats talks JTAG to XC3S and XCF via FT2232. It
knows about JTAG speed. Let me know if you are interested (and willing to
give feedback).

-- 
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

Uwe Bonnes schrieb:

>>The speed setting in impact apparently doesn't apply to my Parallel
>>Cable 3.
> 
> 
>>>Another option beside the USB Extender is to convert the levels to a
>>>RS422/485 signal and use a twisted pair cable.
> 
> 
> The FTDI FT2232 happily generates serial protocols. I have a modified version
> of Andrew Rogers's xc3sprog thats talks JTAG to XC3S and XCF via FT2232. It
> knows about JTAG speed. Let me know if you are interested (and willing to
> give feedback).

I guess the point is, that the OP want a quick & dirty solution, wich is 
most probably not possible due to the high delay of 100m cable (which is 
~500ns). Even optical fiber would be that slow.

Regards
Falk