Re: [Discuss-gnuradio] forecast method for HDLC transmit block

[Ed Criscuolo]

Eric Blossom wrote:
> Ed, 
>
> The problem is that you need to know when the output is about to
> underrun, and only then insert flags.
>
> Is there any external reference clock or other way to tell when the
> external stream needs data?   In general, GR has no tie to an external
> timebase, except indirectly through sinks or sources that consume data
> at a fixed rate (e.g., USRP, audio card, etc).  If there is some way
> to tell when the external world is ready for more data, we can solve
> this problem.  

The data stream needs to be at a fixed rate.  I was planning to add
a throttle block to insure this.

> Is the USRP the final sink for the modulated bits?

Yes, after it's upsampled and modulated, the USRP is the final sink.
I realize that this should pace things, but I figured the throttle
block would be a good idea in that it would allow me to test
without a USRP hooked up, just a spectrum display.

At this point, I think I'll embed all the packet reading AND
hdlc processing into a single source block with no flow
inputs.  This way the block can check for packets on the TUN
device, read them, bitstuff and hdlc frame them, and put them
into an internal ring buffer. Then it would return as many bits
as requested, or flags if the ring buffer was empty.

I'm assuming that the scheduler would keep asking for enough bits
from this source block to keep the flow going at the throttled rate.
(assuming I have enough CPU power to keep up).

Does this approach sound like it will work?

@(^.^)@  Ed