General Technical Discussion

[abie_anaton]

Hello,

My question regards the SPARTAN-6 FPGA PLL device.

I am developing a project that uses PLL, which is rives with one of its output clocks to a BUFPLL device.

When implementing the design, the PAR (Place And Route) tool fails to route the design.

The error message is the following:

  Unroutable signal: CLKx10_sig pin:  my_interface/my_interface/ioclk_buf/PLLIN 

In essence, the output clock from the PLL (signal CLKx10) cannot be routed to the BUFPLL (ioclk_buf).

I verified in the SPARTAN-6 CLOCK RESOURCES GUIDE that the two cites (PLL and BUFPLL) can be 

routed together, so this is not the problem.

As far as I understand, the PLL output clock should be connected directly to the BUFPLL input port (PLLIN).

What am I doing wrong here?

Can someone advise me what to do?

Thanks,

Abie Anaton

[eteam00]

The Spartan-6 has an interesting set of interconnect resources.

Please list all of your clocks, and how they are buffered, and any constraints you have placed on those clocks and bufffers.  You may be exeeding your buffer budget, or you may have run out of interconnect.

-- Bob Elkind

[abie_anaton]

Hello again,

I run the following clocks:

1 - the PLL input clock (CLOCKIN) is routed from an external clock pad through a BUFIO  buffer.

2 - the PLL output clock (CLOKOUT) drives the FPGA logic and is routed with a BUFG buffer.

3-  the PLL second output clock (CLOCKOUT1) is connected to a BUFPLL primitive (GCLK port) and is  routed with a BUFG. 

4- the PLL third clock (CLOCKOUT2) is connected directly to a BUFPLL primitve (PLLIN port)

 My design implements a DVI transmission (Tx) controller. I take a pre-defined pixels data and transmit them using

 a DVI encoder outside to the TDMS FPGA ports, which in turn are connected in my board to an external cable port.

Any advice to my problem will be helpful. Thanks

Regards,

 Abie

[eteam00]

I'm guessing that this is the clock signal which isn't routing.

4- the PLL third clock (CLOCKOUT2) is connected directly to a BUFPLL primitve (PLLIN port)

Here's a suggestion:

"Comment out" the pin assignments for the TMDS output pins which are driven by the BUFPLL/OSERDES2 blocks.  Let the ISE tools auto place these pins.  I guessing that the pins assignments for these TMDS outputs may be the underlying interconnect problem.  Of course, the location of the BUFPLL must be unconstrained as well.  See it the map/place/route processes complete successfully.

Just a guess.

-- Bob Elkind

[abie_anaton]

Hello Bob,

Your guess is right, the BUFPLL PLLIN input port signal is the one that the PAR tool cannot route.

Unfortunately, I cannot comment out the TDMS FPGA pins, as their locations are dictated by me by the SPARTAN-6 FPGA

ATLYS board (Digilent Inc.).

However, I verified that the PLL buffer primitive location cite complies with my PLL primitive location (by reading

table 3-1 in the SPARTAN-6 clocking resources guide).

I have a question, though:

1 - Are their any limitations about which PLL output clock ports can be routed to a BUFPLL primitive?

     Is it possible that I routed a non-allowed CLOCKOUT port to the BUFPLL input PLLIN port?

Best Regards,

Abie

[eteam00]

Are their any limitations about which PLL output clock ports can be routed to a BUFPLL primitive?

Is it possible that I routed a non-allowed CLOCKOUT port to the BUFPLL input PLLIN port?

BINGO!  You found the problem.

From UG382 page 96:

BUFPLL and BUFPLL_MCB input clocks can be connected to either CLKOUT0 or CLKOUT1 from the PLL.

An example of a not-entirely-useful error message.

-- Bob Elkind

[abie_anaton]

Thanks Bob.

You really helped me solve it.

I'll look into it soon and give you a feedback if it will be solved.

Best Regards,

Abie

[abie_anaton]

Hello Bob,

I made the changes we discussed upon, and indeed the problem was solved.

I was able to synthesize the project with the ChipScope project, and now I'm prepared to check the design.

I now hope that my design will be able to drive the DVI data through the board's connectors outside in the correct manner.

Thank you again for your kindly help and support.

Regards,

Abie Anaton

[laxus]

hello

I want to run a simple programe on spartan 6 (I work with ise 12.3)

and I don't know what need to be connected (which cables).

do I need anyway 2 cables of USB?

please write in detail.

thank you

[eteam00]

laxus,

Please start a new thread.  When multiple topics are discussed in a single thread, it makes a mess of both discussions.

-- Bob Elkind