Digital Discovery issue and question

[sintech 0]

Hi, I'm a new DD user.

WaveForms beta 3.11.25 (Windows 10) and 3.11.24 (Mac OS)

1. I have noticed that if I change acquisition mode in Logic Analyzer, manual order of bits in Bus got rearranged.

2. Is it possible to capture data for more than "base" amount of time in Record mode? For example, I would like to capture 20s of samples at 20Mhz in 16x400Mhz config for further analysis.

My expectations for Record mode were that DD streams captured samples via USB to WaveForms using DD's large 256M buffer as FIFO. So I thought the capture time would be limited only by PC memory size.

 

Thanks,

Konstantin

[attila 489]

Hi @sintech

1. Thank you for the observation. It is fixed for the next software release.

2. The number of samples is limited in the WF application for GUI performance reasons.
With the WF SDK you could record 'unlimited' number of samples. However the recording rate is limited due to USB 2.0 bandwidth to about 1MHz at 32bit sampling, 4MHz 8bit sampling.
With Digital Discovery you can record up to 256M samples with 8bit sampling up to 800MHz. The transfer of the captured data to computer will be at slower USB rate.

[sintech 0]

38 minutes ago, attila said:

With the WF SDK you could record 'unlimited' number of samples. However the recording rate is limited due to USB 2.0 bandwidth to about 1MHz at 32bit sampling, 4MHz 8bit sampling.

Thank you for the answer.

Do I take it right that it is not possible even using WF SDK to record more than one buffer size holds without skipping at high sample rates (more than 1Mhz at 32bit)?

Can you please clarify the example I mentioned (20s of samples at 20Mhz in 16x400Mhz)? If I use SDK, is it possible without sample skipping?

 

[attila 489]

Hi @sintech

It is not possible. Streaming over USB at 20MHz (>2MHz x16) is not supported. The 20MHz x 20s = 400M > 16x128M (2Gbits DDRAM of DD)
With DD you could capture 128M samples of 16 bits at up to 400MHz, or 128M at 20MHz (6.71sec) or record 'unlimited' at ~2MHz.

[attila 489]

Hi @sintech

The Bus order is fixed in the latest WF beta:
https://forum.digilentinc.com/topic/8908-waveforms-beta-download/

 

[sintech 0]

Ok, got it.

Does it make sense then to implement "Data Compression" for DD as it was done for AD2?

Because my device operates mostly in idle mode with short bursts of data exchange.

As I understand, the "Sync" mode can be used for this purpose. DD will fill it's buffer only when Enable signal is active while data will be transmitted to WF during idle state.

 

[attila 489]

With data compression half of the buffer size is used for storing time/delay. In worst case scenario, this reduces the buffer bandwidth to half.
In case you are not interested in sample timing, you could use 'sync' mode .