Oscilloscope Interleaving clarification

[diggit]

I am poking around Rigol Scope sources (#943) and Interleaving confuses me.
What is considered as interleaving? I noticed #578 where @azonenberg writes about automatic interleaving. Isn't that what scopes with single shared ADC are doing?

Reading though [Oscilloscope.h] header and it does not help.

scopehal/scopehal/Oscilloscope.h

Lines 538 to 546 in 80fdea6

	/**
	@brief Get the legal sampling rates (in Hz) for this scope in all-channels mode
	*/
	virtual std::vector<uint64_t> GetSampleRatesNonInterleaved() =0;
	/**
	@brief Get the legal sampling rates (in Hz) for this scope in combined-channels mode
	*/
	virtual std::vector<uint64_t> GetSampleRatesInterleaved() =0;

I understand the user docs and v0.1 are main focus now, but this topic really confuses me and I'd like to implement things properly.

[azonenberg]

So, this is a bit of a sticking point API wise.

The interleaving stuff in the API is generally based on the assumption that you have something similar to what e.g. most LeCroy scopes do, where you have one ADC per two channels and there is a manual, user-controlled switch between running all channels at the standard sample rate, or half the channels at double rate. Or alternatively, no interleaving control at all (one ADC per channel so sample rate is not dependent on which channels are active)

Other scopes (like Rigol and Pico) have more complex structures that are generally managed internally by the instrument, rather than exposed in a setting the end user can control. We thought about it for a while in #64 and for now have settled on the current situation: From the API's perspective, this is considered "not interleaving" at all times, but the set of available sample rates returned by GetSampleRatesNonInterleaved() is going to vary depending on which channels are currently turned on.

We recognize that this isn't ideal, but haven't come up with a better API for expressing this more complex interleaving model well.

[diggit]

So if I understand correctly, Interleaving API is for scenarios where you have to configure it manually (not handled automatically by the scope). In Case of Rigol scopes, HasInterleavingControls() should return false and all interleaving function could be kept empty/reject requests. Am I right?

[azonenberg]

Yes, that is correct.

Longer term we want to have APIs to at least expose the status/legal values of automatic interleaving (e.g. have some way to explain via the API that you can do 4x 250M / 2x 500M / 1x 1000M, but not 4x 1000M). But that's currently not possible, all you can do is set the requested sample rate and determine what rates are available right now with the currently active set of channels.