Digital Discovery and Platform Cable

[wlevans]

I am working an a design based on a microZed, which requires me to interface to it via JTAG with a Platform Cable USB II from Xilinx. I am using the Digilent Digital Discovery to verify the SPI signals from the microZed. My problem is that when the Digital Discovery is connected, it interferes with the Platform Cable. The SDK connects to the Platform Cable, but it cannot find the target (microZed). Once I unplug the Digital Discovery, the SDK finds the targets as expected.

Has one else ran into this problem and overcome it?

Willy

[attila]

Hi @wlevans

Which Xilinx software and version are you using?

 

Hi @malexander 

Did you notice such conflicts?

[wlevans]

Hello Attila,

I am using Xilinx Vivado and SDK 2016.4.

WaveForms version 3.7.5 64 bit.

 

Willy

 

[malexander]

@attila

I couldn't get the Platform USB Cable II that I found in our office to work at all (not in impact or Vivado on Windows 7 or Windows 10) regardless of what devices I have plugged into my PC. I think it's physically damaged in some way because iMPACT keeps saying it can't detect VREF on pin 2 but the XUP USB Cable I have works fine plugged into the same target. The XUP USB cable is pretty much equivalent though so it should work for testing scenarios like these.

I was able to replicate the behavior described by @wlevans one time, and only one time, by connecting the XUP USB cable and Digital discovery to my PC and then running Auto connect in Hardware Manager 2016.4. Hardware manager incorrectly tried to open the Digital Discovery, and for whatever reason, made no attempts to open the Xilinx cable. After I opened the Digital Discovery in Waveforms, which locks the USB interface, Vivado stopped trying to open it and would then correctly open the XUP cable. I tried closing all software, disconnecting everything, and reconnecting it to see if I could repeat this behavior but now Vivado does not see the Digital Discovery even when it's not open in Waveforms and it manages to open the XUP cable.

The initial behavior I observed leads me to believe that Xilinx is giving preference to Digilent JTAG cables over their own cables, that they are incorrectly opening the Digital Discovery (they shouldn't because the firmware ID and PDID are wrong), and that they give up after the first failure to initialize a scan chain. This is definitely a bug in Vivado and at the moment there are two workarounds I can recommend:
1. Connect only the platform USB cable initially, start hardware server, and connected to the MicroZed. Then connect the Digital discovery to the PC.
2. Connect both devices but open WaveForms and have it connect to the Digital Discovery prior to launching hardware server. This will lock the USB interface and cause Vivado to skip over it.

If I can figure out how to reproduce this behavior more consistently then it should be possible to have it fixed in future versions of Vivado... probably 2018.3 or later.

[wlevans]

Based on the advice from tiem 1 above, I can get it working (most of the time, but not always) by doing the following:

1. Plug in Platform Cable (wait until all enumeration "beeps" stop).

2. Start SDK.

3. Program FPGA.

4. Plug in Digital Discovery.

5. Start up WaveForms.

Though it doesn't work all the time, it usually does after 1 to 3 attempts. I could not get it working by following item 2 at all.

Thanks for the advice!

Willy