Re: [sigrok-devel] Several questions for supporting usbee dx

[Bert V. <be...@bi...>]

On Thu, 19 Dec 2013 14:42:29 +0900, Jong-Jin Kim
<jon...@gm...> wrote:

> I sent several patches for usbee dx yesterday, but I'm not sure that
> those meet your requirements.

I have some comments on those, will reply to the patches with comments
in line. Don't take them as criticism though: it's great to see
somebody taking on this hardware/clone.

> 1. usbee dx analog signal has some delay, compared with digital
> sample of the same signal, about 180ns when captured 1Mhz square wave
> signal with 12MHz sampling rate. Delay becomes longer with lower
> sampling rates. I think this can be synced on GUI front-end with
> analog signal drawing in a time-shifted way. I checked pulseview's
> signal drawing routines but it's beyond me. Could you give me any
> hint?

This really belongs in libsigrok.

We need to come up with a way to assign a time offset to data coming
from an sdi, and a way to link two sdis together. Since the time offset
can change during capture, for example after buffersize change or as in
your case, samplerate change, clearly it'll have to be via an
SR_DF_META packet.

Feel free to come up with suggestions, or join us on IRC as Joel
mentioned, to join in the discussion.

> 2. I think libsigrok supports several oscilloscopes and it might have
> a device configuration enumeration value for analog trigger level,
> but I can't find it. should it be defined as something like
> SR_CONF_TRIGGER_LEVEL?
> 
> I know sigrok and pulseview is designed for logic analyzer mainly, and
> supporting other devices like oscilloscope is in work-in-progress. I
> think generalized device configuration values for a specific device
> category like oscilloscope is useful, otherwise libsigrok would have
> a bunch of duplicated, device-specific configuration enumeration
> values. Of course, defining those values needs insight and knowledge
> of various measurement devices. Oh, its not an easy job.

Supporting oscilloscopes is indeed still a WIP as you noticed, and
we're still missing some config keys like that. Feel free to define
that key and use it in your driver. I'd suggest voltage as float, for
the value.

At some point we'll consolidate some of those keys and data types into
more sensible ones, but you shouldn't let that stop you -- part of
that job is fixing up all the drivers that use them.


-- 
Bert Vermeulen        be...@bi...          email/xmpp