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Nexys 4 DDR always is busy


PartyArty

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Hello,

Next to the VGA connector you can find the MODE jumper block. There are two things I want to ask you to try.

1. Set the jumper to QSPI and power on the board. The BUSY led should light up for ~ 1 second and then it should turn off and the board should be running the Demo project stored in its flash memory. 

2. Set the jumper to JTAG and then power up the board. Again, the BUSY led should light up for a short time and then turn off. You should then be able to use the board in the Vivado hardware manager.

Please let me know how the board behaves in these circumstances. 

Sergiu

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I did that and the demo project ran. However, when I connect it to Vivado and open up the hardware manager, I get the following message: 

 [Labtoolstcl 44-494] There is no active target available for server at TCP:localhost:3121.
 Targets(s) ", jsn-Nexys4DDR-210292744880A" may be locked by another hw_server.
 

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I don't mean to crash your party Arty but I am chasing a very similar issue with a different Digilent part. I was curious if my symptoms matched yours. I am using a Digilent JTAG-SMT2 board with a Xilinx Kintex Ultrascale XCKU060 target. If I power down the Target and the JTAG-SMT2 while Vivado 2015.4 has the target open, once I power things up again I get exactly the same messages you showed above. I am only able to reconnect with the target if I either reboot my server (repeatable on multiple servers), or disconnect and then reconnect the USB cable serving the JTAG communication.

Have you tried either of these remedies to see if you can reconnect to your device?

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Hi, PartyArty,

I think I've run into similar issues before, and the fix has been a reboot of the hw_server. Specifically, I think I went into task manager while Vivado was closed and found that a hw_server task was still running. Ending this task and relaunching Vivado usually fixed the issue, if I recall correctly. Not sure if you've tried this specifically, or something to the same effect.

Thanks,

Arthur

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I don't think my issue was the same as PartyArty since a reboot or power cycle apparently does not allow Vivado to rediscover his FPGA device. However in case others land on this thread that have similar symptoms I thought I would post what I discovered my issue to be.  Turns out many USB cable powered devices (like JTAG, serial console, etc.) remain powered from the server they are connected to even if the target FPGA are powered off. This means they can continue to drive signals to the target FPGA. In my case there was a parasitic path from an adjacent USB serial console signal through the ESD protection devices in the FPGA (powered down), which then partially powered a voltage rail shared by the Digilent JTAG-SMT2. The 3.3 voltage rail on the Digilent part measured about 1.3 volts. This apparently was enough to make the server think the JTAG was there but unresponsive. This state is not cleared when power is restored to the Digilent part (bug?). Thus the reboot, or cable pull.

We added some circuits to address this parasitic path in our hardware such that the power to the JTAG-SMT2 is driven below 0.4 volts when the target is powered down. Voila!, Vivado automatically reconnects with the Target FPGA when power is restored.

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