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Re: [Discuss-gnuradio] Expected behavior during underruns

From: Josh Blum
Subject: Re: [Discuss-gnuradio] Expected behavior during underruns
Date: Wed, 15 Dec 2010 11:04:26 -0800
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20101208 Thunderbird/3.1.7

> It would be really nice if the send-function in the API have a TDMA
> mode where fragments of samples are dropped when an underrun occur so
> that the majority of the samples are aligned to the
> start_of_burst_time (see above example (1) and (3)). With this
> feature it is not necessary for the programmer to know if an underrun
> has occurred and how to handle this. Instead the programmer knows
> that if an underrun occurred some samples are dropped but the rest of
> the sample are transmitted at the expected time without any offset.
> Is this doable?

This should already be the case. If you timestamp every packet, then the
underflow recovery is handled by hardware. That is, the FPGA will drop
until the timestamp is <= current time, and then wait until the
timestamp == current time, so realignment is automatic.

Are you timestamping every packet? This calculation should be
last_time_spec + time_spec_t(0, num_samps_in_last_packet, host_sample_rate)

Let me know if you are not seeing this behavior.

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