Scope - record - after stop position not aligned

[kojak]

Hello @attila

I think this is a bug. My setup looks like:

• Wavegen is started by Script
• Scope is triggered by Wavegen configured to record 2 Msamples. Trigger set to 10%
• Logic is triggered by Signal and configured to measure very short period of time

In a script I Start Logic, then Scope and wait for scope to prefill. Then I start Wavegen, which triggers Scope. After some time Signal triggers Logic which is Done a little after that. Then Wavegen and Scope is stopped by Script. After that Scope data are shown correctly, but they are shifted from the defined trigger position. Do you think that it will be possible to align them to the right position?

Thank you

[attila]

Hi @kojak

Could you post the workspace?

[kojak]

Hello @attila

No, I can not provide it, it is confidential. What informations do you need?

[attila]

Hi @kojak

I'm not sure how exactly you are configuring the interface, but stopping the capture from Script has a few milliseconds of uncertainty.

I think it would be easier to configure the Wavegen to trigger on Scope and have in Scope trigger None, like this:

[kojak]

Hello @attila

I do not write it clearly. I do not have an issue with delay caused by Script, but when Scope is stopped (by Script) in the middle of measurement. Then when data re displayed, then they are not aligned to the trigger.

[attila]

Hi @kojak

Don't stop the recording process, let it stop automatically.

The recording continuously captures data and stops after it collects the required post trigger samples. Then it aligns the data according the trigger position.
If you force stop it it does not have sufficient samples, it can't align the data.

[kojak]

Hello @attila

I can not let it stop automatically as I need to stop it as soon as event on Logic appears in order to have measurement as short as possible.

But trigger should be in measured data, so I think that alignment should be possible. Do you think that it will be possible to implement?

[attila]

Hi @kojak

You could use the Scope in mixed mode, with Logic Analyzer in it and trigger on digital signal, set the trigger position to 90%, to be a record stop condition.
If you prefer you can use Scope and Logic separately and select one to trigger the other.
You could also hook the digital signal to the trigger signal and select trigger source External 1/2

Scope.run()
wait(Scope.Time.Base.value) // make sure to have pretrigger data
Wavegen.run()
Scope.wait()
Wavegen.stop()

[kojak]

Hello @attila

please see my modified workspace.

Scope_offset_issue_no_data.dwf3work

[attila]

Hi @kojak

In case you want to stick to your triggering method, leave more prefill time for the scope, so when you stop it to have at least the specified number of samples collected. This way when stopped it can align the data, such a way that the last captured sample to be at the end. In case it does not have sufficient samples it won't perform this alignment.

[kojak]

Hello @attila

How much samples should I let to capture? I think samples up to trigger point should be sufficient? Is there in data from FPGA information when trigger appear?

[attila]

Hi @kojak

The recording process streams in data into a circular buffer, similar to scan screen.
Normally after the trigger event it collects the remaining samples, according trigger position (like 50%), then stops and aligns the data so the last sample to be on the right.
When you stop the recording, it it should have at least the specified number of samples for recording in order to perform alignment, so the last recorded sample will be on the right.

[kojak]

Hello @attila

Now I understand how this is working. So I need to have all samples which I defined to capture.

Do you think that it will be possible to transfer information at what sample is trigger and align samples to this point (if there are missing samples after trigger) or this will be much work to be done?

[attila]

Hi @kojak

In case the record does not collect suffice data, it is stopped before it reaches the specified number of samples, it can't do alignment. The right side of the buffer won't have data.

[kojak]

Hello @attila

OK, I will use your the first proposal. There is little about 2 us offset (measured signal from Wavegen on Scope is about 2 us delayed after trigger), but this is acceptable.

Thank you

On 1/29/2019 at 6:15 PM, attila said:

Hi @kojak

I'm not sure how exactly you are configuring the interface, but stopping the capture from Script has a few milliseconds of uncertainty.

I think it would be easier to configure the Wavegen to trigger on Scope and have in Scope trigger None, like this: