Re: [Discuss-gnuradio] packet_pad_impl in gr-foo

[Bastian Bloessl]

Hi,


> On 3 Mar 2017, at 07:15, Nikita Airee <address@hidden> wrote:
> 
> I would like to time synchronize transmission in two USRPs. I understand that 
> after synchronizing pps and 10MHz, I would have to make use of time tags. For 
> that I looked to packet_pad_impl in gr-foo.
> 
> When I use the block with a flowgraph, specifically the example flowgraphs in 
> gr-ieee802-11, it really just blocks the transmission, meaning no data is 
> transmitted from the USRP. The loopback too doesn't work. Tag debug also 
> doesn't show the presence of any tags(tx_eob, tx_sob, tx_time etc).
> 
> Is the block not working or am I doing something wrong? If at all I 
> completely misunderstood the purpose of the block, could you please point me 
> in the right direction for implementing time tags as well? 

I don’t get what you mean. Could you please describe a bit more detailed what’s 
happening.

The gr-ieee802-11 flow graph uses “Packet Pad 2”, a Tagged Stream Block that 
just pads some 0s. It doesn’t block. When you enable the delay option, it will 
add a “tx_time” tag that can be used to delay the transmission. (The delay is 
added by the USRP, i.e., also in that case it doesn’t block).

Best,
Bastian