Scan vectors--pattern generation problems (PXI-6541)

[jcao]

Hi,
 
I would like to use PXI-6541 (HSDIO) to send scan vectors to the DUT. The pattern file generated by the designers group are in four possible formats: WGL, STIL, VERILOG_SERIAL, VERILOG_PARALLEL.
 
Question:
Which software should I use to import the pattern file?  I tried "Digital Waveform Editor". I am not sure whether this is the right software to use. It seems like it can only accept ASCII or VCD file. Maybe I am not using the right software?
 
Thanks a lot,
Jing
 

[jcao]

HI Jaime,
Thanks for your reply. Finally I got a VCD file and imported it into the Digital Waveform Editor. However, I got the following message:
"To respect the timing information defined in the VCD file, the imported waveform must be generated with the following frequency: 20 GHz."
What does this mean? My clock signal is only 500Hz. Why do I need to change the rate into 20GHz?
Thanks a lot!
Jing

[Chris J B]

Hi jcao,


The Digital Waveform Editor imports VCD files and formats
them in such a way that HSDIO devices can use them. This formatting includes
setting up the necessary resolution to take into account the accuracy of each
signal?s edge transitions and their relative positions to the clock edges. I
believe the issue you are referring to is a result of the timing resolution
that has been implemented in your VCD file.  For example, if you are using Pico- or Femto-
second precision you would need a possibly unrealistic device sample clock to
handle it.


Below is another post which I think might be related to your
issue. Although the primary topic concerns another error code involving the
importing of VCD files, it goes on to discuss the resolution and accuracy of
digital edge transitions in a VCD file and how this might affect the necessary
sample clock rates.


<a href="message?board.id=70&amp;message.id=1811&amp;view=by_date_ascending&amp;page=1" target="_blank">Can't
import VCD file in Digital Waveform Editor</a>


If possible, it would be helpful to post an example VCD file
that results in this error. I would be happy to take a look at the file and see
if I can confirm that this is the cause of your troubles. &nbsp;

[JaredW]

jcao,
Whenever we see the Digital Waveform Editor wanting to import a VCD file&nbsp;with an elevated generation frequency, it is almost always due to the fact that the VCD file has edge transistions that don't align to a specific cyclized boundary.
In your case you mention that your test pattern should be generating at 500Mhz. Therefore you would expect that edge transitions in your VCD file are only occuring every 2ns. However, what is actually happening, is that your VCD file has some edges that transition ~50 picoseconds before or after the 2ns boundary. This is causing the DWE to want to oversample data from your VCD file and generate at a higher frequency (20GHz) in order to preserve this precise timing.
Based on the warning message you mentioned in your post, I believe you are using an older Digital Waveform Editor. Possibly v1.0.&nbsp; I'd recommend updating to atleast v2.0. Version 2.0 added some new features to the VCD importing tool to address this oversampling issue. The new feature allows you to import data from your VCD file at specific intervals of time. The specific internval can be based on a clock signal within the VCD file, or based on a user specified interval. The benefit of using a specific interval or clock signal for importing is that any edge that is just a few picoseconds outside of the expected boundary will be either pulled into the previous boundary or pushed out to the next boundary.
You can download a trial version of the DWE v2.0 from our website, NI.com.<a href="http://sine.ni.com/nips/cds/view/p/lang/en/nid/13050" target="_blank">http://sine.ni.com/nips/cds/view/p/lang/en/nid/13050</a> Look for the Resources tab, and you will see a link to Evaluation Software.
The last post from Chris J B refers to a very old post which does not detail how to get around the issue, but that post does contain a detailed description of why the DWE is trying to import your VCD file with a 20Ghz clock.Message Edited by JaredW on 10-15-2007 03:30 PM

[jcao]

Hi,
I downloaded DWE 2.0 demo and tried to import VCD file.
As a first try, I imported only a 500HZ CLK signal at "select signals", "Select Sampling Method" as "Fixed Timebase or Rate", choose "Cycle Time for Sampling" as 10ns, "Frequency for Sampling" for 100MHz, "Sampling Starting Position" as 5ns, "Configure X and Z states" all as default. After I click "Finish", the error message is
"Waveform must contain 2 or more samples."
Can anybody help me on this? This is so frustrating. It's supposed to be a fairly simple process. I don't understand why DWE just can not do it!
Thanks,
Jing

[JaredW]

Jing,
Your settings sound resonable assuming the signal you selected in import really is a 500Hz signal.
The DWE has a requirement that any waveform it has open in memory must contain no less than 2 samples of data. If a waveform file or imported VCD file only has 1 or 0 samples of digital data, the DWE will give an error and cancel the open/import operation.
There may be an issue in your VCD file. Maybe the timing that you expect the VCD file to have is not the actual timing. I would like to get two pieces of info from you.
1)&nbsp;Go to&nbsp;the VCD Wizard configuration page were you set the import timing. Instead of doing 100MHz, could you instead click the "Retrieve From File" button and then post the results that it finds into the message post. This button will scan the file and try to find the best import timing for the signals you selected to import.
2) I would like to get a look at your VCD file. Maybe not the entire thing, but a snippet of the first handfull of timestamps. Could you either add your VCD text file to this thread, or maybe edit it in a text editor such that we could atleast see the header for the file and a handfull of timestamps?
Thanks,Jared
&nbsp;

[jcao]

Hi JaredW,
Thank you so much for&nbsp; your help!
1. Yes, I indeed tried to "retrieve from file" to get the information of sampling frequecy. Unfortunately I got this error message:
"Import sampling configuration is invalid. The selected cycle time or frequency may be invalid."
The "Cycle Time for sampling" is 0s, Frequency is Inf Hz, while Sampling start position is 0s.
2. Attached please find the vcd file. It's a short version, the first 5 vectors only.
&nbsp;


VECTORS_SHORT.zip:
http://forums.ni.com/attachments/ni/70/7672/1/VECTORS_SHORT.zip

[jcao]

Hi JaredW,
I imported the new VCD file with DWE2.0. Strangely the CLK500H signal I got is an all-ONE signal. Attached please find the VCD file.
Thanks,
Jing


VECTORS_SHORT.zip:
http://forums.ni.com/attachments/ni/70/7685/1/VECTORS_SHORT.zip

[JaredW]

Jing,
&nbsp;
I just imported your vcd file using the following values: 2us Cycle Time or 500kHz Fequency for Sampling. (These are the values that the DWE importer suggests using the "Retrieve From File" button)
&nbsp;
First thing you should notice about the DWE is that after an import operation, the waveform editor is only displaying the first 100 sample or so. Be sure you are zooming out to see the entire waveform. When I first imported your VCD file, I too only saw all 1's, but when I zoomed out to see the entire waveform I started to see some edges.
&nbsp;
After looking at both your VCD file and the imported DWE waveform that I get using the above timing, it looks like the CLK_500H signal is not a perfect clock. It is mostly high execpt for 2 very short periods of time where it drops to low. It is only low for about 4-6 microseconds then goes back to high for 4000-5000 microseconds. These 2 moments where the clock goes low are also not on a 500Hz boundary. Therefore, if you are trying to import this signal using a 500Hz sample rate, you will only see all 1's. I'm not sure if this CLK_500H signal is supposed to be a perfect 50% duty cycle 500Hz clock, but looking at your VCD file in notepad, I can tell you it is not. There may be an issue with how you are are simulating the VCD file.
&nbsp;
Looking at the VCD file in notepad, I found that the CLK_500H signal changes state at the following timestamps: X at 0 microseconds, 1 at 40 microseconds, X at 1370 microseconds, 1 at 1374 microseconds, 0 at 4110 microseconds, 1 at 4116 microseconds, 0 at 9598 microseconds, and 1 at 9604 microseconds. A 500Hz signal should be transitioning around every 2000 microseconds.
&nbsp;
-Jared
&nbsp;
&nbsp;
&nbsp;

[jcao]

Thanks a lot JaredW. That solved the problem.
I realized that importing a VCD file into the DWE takes very long time (hours for a 50Mb file). My computer is PXI-8106. Is there any way to speed it up?
Thanks,
Jing

[jcao]

Hi JaredW,
I just realized that I never replied your post. Yes, I have upgraded to Waveform Editor Version 3.0, and it indeed helps.
Thanks a lot for the nice suggestion!
Jing