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Reduce sample resolution in streaming mode

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Reduce sample resolution in streaming mode

Postby jacob.larsen » Mon May 05, 2014 12:38 pm

Hi

We are currently ordering a 6404D, and I am exploring bonus features, e.g. streaming mode via SDK.

Is it possible to lower the sample resolution in order to be able to hit higher sample rates in streaming mode? For example if I am sampling a digital signal, then I might just be interested in knowing if each sample is above or below a threshold voltage (logic analyzer). It looks like you are currently sending 16 bit samples over USB3 in the standard API, but if that could be reduced to 1 bit per sample, we could get up to 16 times higher sample rates in the same setup.

I have previously used the small USBee logic analyzers and the feature where they capture to a huge buffer in the PC RAM is extremely useful (in the old software, their "Suite" broke some of that, also only the old SX/AX devices). It could be very useful if I could use the Picoscope as a high-powered version of these with high sample rates supported by USB3.

/Jacob
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Re: Reduce sample resolution in streaming mode

Postby Hitesh » Fri May 09, 2014 9:04 am

Hi Jacob,

The driver will only return 16-bit values (which are scaled from 8-bit values). You can use downsampling to return average, decimate or aggregated (min/max) data.

What sampling rates are you looking for? You should be able to achieve around 156MS/s with a single channel.

I will pass on your suggestion as a new feature request.

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Re: Reduce sample resolution in streaming mode

Postby jacob.larsen » Tue May 27, 2014 7:56 am

I am specifically looking at a digital signal clocked at 200MHz. So sample rates of about 800Msps with 1 bit resolution would be really useful here.
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Re: Reduce sample resolution in streaming mode

Postby Hitesh » Thu May 29, 2014 10:57 am

Hi Jacob,

How long do you need to capture data for?

You could use a block mode capture for data acquisition for a short period of time. The sampling rate would either be 625MS/s or 1.25GS/s although you might be able to use downsampling if you use the fastest timebase (single channel only).

The data will be 8-bit values over the USB connection and then scaled to 16-bit by the driver.

Hope this helps.
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Re: Reduce sample resolution in streaming mode

Postby jacob.larsen » Mon Jun 02, 2014 7:35 am

As long as possible, but the usual sweet-spot has been around 30-60 seconds when using the USBee's.

The signal would need at least 3 channels to get the most valuable information. A complete signal decode would require 6 channels, but we haven't found any hardware with that many channels in this class.
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Re: Reduce sample resolution in streaming mode

Postby Hitesh » Mon Jun 02, 2014 8:28 am

Hi Jacob,

A complete signal decode would require 6 channels, but we haven't found any hardware with that many channels in this class.


With regards to the above, are you referring to the sampling rates possible for streaming?

The PicoScope 4824 is an 8-channel oscilloscope with 12-bit resolution and has a maximum sampling rate (single shot) of 80MS/s.

http://www.picotech.com/picoscope4824overview.html

Best wishes,
Hitesh

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Re: Reduce sample resolution in streaming mode

Postby jacob.larsen » Mon Jun 02, 2014 8:59 am

The 4824 only has 20MHz bandwidth, which is what I was referring to when I said "in this class". We got a 6404D, which has 500MHz bandwidth. This fulfills our primary goal with the purchase, and my current investigation focuses on trying to see if we can get more out of the investment.

The specific case is 4-bit SDIO running at 200MHz. Obviously some information will be lost as we only have 4 channels available, but since you can get 95% of the information from 3 channels (CLK, CMD and D1/IRQ), this is not a big loss. It just means that the data cannot be decoded, but since debug that involves data normally comes at higher levels in the stack, this is not critical.

Anything that can get us closer to the 1-bit streaming mode on 3-4 channels with as high sample rate as possible will be helpful.
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Re: Reduce sample resolution in streaming mode

Postby Hitesh » Mon Jun 02, 2014 10:53 am

Hi Jacob,

Thank you for the information.

At the present moment, the driver/firmware will not be able to support the requirement for 1-bit values to be sent over the USB connection to the PC.

Best wishes,
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