Re: [Discuss-gnuradio] [GSOC17 - Draft proposal] Implement SigMF functionality for GNU Radio

[Bastian Bloessl]

Hi,

On 03/24/2017 07:33 PM, Ben Hilburn wrote:
>    - I wonder what would be the workflow when creating a SigMF recording.
>     An issue might be that you cannot immediately write the SigMF meta file
>     during recording. (For example, the hash has to be calculated after the
>     recording. Or the annotations have to be written after the capture
>     segments.). Did you plan to create the meta data in memory and write the
>     file when the flow graph shuts down (which might cause data loss when
>     you experience a segfault) or do you write meta data to disk in an
>     intermediate format that you have to post-process manually to create the
>     final SigMF files.

> 
>     > So the SigMF spec is designed specifically to enable writing the
>     > metadata and dataset files in a streaming manner.
> 
>     Can annotations and capture segments be interleaved or how is it
>     possible to write the metadata in a streaming manner?
> 
> 
> No, they cannot. If your capture details aren't changing (center
> frequency, bandwidth, etc.,), then you can stream the annotations as
> they are continuous, but you can't hop back and forth between them.

But that means in all but the simples case the metadata cannot be
written in a streaming manner. And worse, you cannot know in advance.
If the SigMF sink wrote thousands of annotations and the SDR experiences
an underrun, it creates a new segment and invalidates basically the
whole file. So, AFAIS, we're back at the problem above, i.e., the sink
needs a way to deal with that.

Best,
Bastian