Forum: GNU Radio streaming from file

Hi all,

I am working on a custom block that tags a stream based on a binary file 
stretched into unpacked form:

(1)                              (2) 
(3)
gr_file_source(repeat=false) --> gr_packed_to_unpacked(1, gr.MSB_FIRST) 
--> my_block

I want to come up with a good way to detect in my_block whether the 
stream input from (2) is finished. I guess gr_file_source will return 
WORK_DONE first, but I don't know if/how that ripples down to my_block. 
Basically I want to be able to tag the last incoming sample with an 
end-of-burst tag, but I don't know how to do this without having advance 
knowledge about the size of the source file.

Thanks,
Sean

On Tue, Nov 13, 2012 at 4:32 PM, Nowlan, Sean
<Sean.Nowlan@gtri.gatech.edu> wrote:
> (3)
> but I dont know how to do this without having advance knowledge about the
> size of the source file.
>
>
>
> Thanks,
>
> Sean


Sean,

Yeah, you won't be able to tell if you're at the end of the file or if
the scheduler just passed you 0 items to process. There's no
indication of that.

Probably the easiest thing for you to do is quickly edit the file
source block to generate the tag when it reaches EOF. That should be
pretty straight-forward.

Tom

Good point. That's probably what I'll do.

Is there any way to check whether upstream blocks are done? From 
examining gr_block_executor, it knows how to do this, so would it make 
sense to have it alert downstream blocks?

On Wed, Nov 14, 2012 at 9:35 AM, Nowlan, Sean
<Sean.Nowlan@gtri.gatech.edu> wrote:
> Good point. That's probably what I'll do.
>
> Is there any way to check whether upstream blocks are done? From examining 
gr_block_executor, it knows how to do this, so would it make sense to have it 
alert downstream blocks?

I was thinking about this and then forgot to reply. The answer is, I'm
pretty sure, no (at least, not without added overhead). You'd break
some of the independence of blocks if you tried to organize something
like. What the scheduler does is look to see if anyone has returned
-1, which will happen if a source is finished (like after reading a
file) or from someone like a gr_head block. This propagates down to
the scheduler who uses this info to start cleaning up, which means
pushing through any more existing items through the blocks and to the
sinks. You couldn't really put something into another block because
there still might be items coming to it from upstream even if the
source(s) is(are) finished.

Tom