Re: [Discuss-gnuradio] UHD USRP Sink Stream Tagging

[King Qiu]

在 2012-07-19Thu的 11:38 -0700，Josh Blum写道：
> 
> On 07/17/2012 08:31 PM, King Qiu wrote:
> > Hi Josh,
> > I have done the same work as Alex. I modified the code in
> > gr_message_source. I added a tx_sob tag and a tx_time tag to the first
> > byte of the message, and a tx_eob tag to the last byte of the message.
> > Assuming:
> > 1. there are 100 bytes in a message(or we call it a packet)
> > 2. bpsk modulation is employed
> > 3. set samples_per_symbol to 2
> > So there are 800 symbols or 1600 samples in the packet. 
> > In the output of the gr_message_source block, the 0 byte is tagged with
> > the tx_sob and the tx_time, and the 99 byte is tagged with the tx_eob. 
> > 
> > Then in the output of the symbol map block, the 0 symbol is tagged with
> > the tx_sob and the tx_time, and the 792 symbol is tagged with the
> > tx_eob. 
> > 
> > After pulse shaping filter, the 0 sample is tagged with the tx_sob and
> > the tx_time, and the 1584 sample is tagged with the tx_eob.
> > 
> 
> I think its important to note that certain gnuradio blocks do not pass
> tags because it is undecided how to interpolate the sample index. Tom
> would have more to say about this.
> 
> > My questions are as follow:
> > 1. The 1599 sample is the last sample in the packet, but the tx_eob tag
> > are added to the 1584 sample. So, what will happen to the 1585-1599
> > samples in the usrp? Are they transmitted by the usrp immediately after
> > the 1584 sample? 
> > 
> 
> Yes, these samples will be send ASAP, and they will not have an EOB, so
> the device will regard this as underflow
> 
> > 2. Is it necessary to adding the tx_eob tag exactly to the last (1599)
> > sample? How can I do this?
> > 
> 
> The sample index is one of the parameters of the tag
> 
> -josh