How the upstream block of TDMA engine get the current time of the network

GNU Radio
1

Previously, the pre-cog introduced a simple implementation of TDMA:
http://gnuradio.4.n7.nabble.com/Introduction-to-Pre-Cog-td37906.html

I read roughly the code in the tdma_engine.py.
For the transmitter, it seems that this tdma_engine works like a
throttle
to send the messages to the downstreams only when the time_update is
later
than the time_transmit_start.
And these time are computed based on the tags in the incoming items
inserted by upstream block.
My question is that, where does the upstream block get the correct time?
I
know that the usrp_sink can get_time_now but it is on the very
downstream,
and it is different block which means different thread.

If my question is not clear, please give your comments.

Thanks.

–

Alex,
Dreams can come true just believe.

2

On 02/04/2013 01:32 AM, Alex Z. wrote:

know that the usrp_sink can get_time_now but it is on the very downstream,
and it is different block which means different thread.

If my question is not clear, please give your comments.

time indication should be coming from the usrp source block. the rx
samples are timestamped, which allows the engine to line up with a time
slot

-josh

3

Hi Josh,

Sorry the unclear question. Actually I am asking how the transmitter
organize the TX samples to the specified time slot…

On Mon, Feb 4, 2013 at 9:45 AM, Josh B. [email protected] wrote:

than the time_transmit_start.

–

Alex,
Dreams can come true just believe.

4

Alex,

I’m on a machine without GNU Radio installed, so I have to confirm that
I’m
actually sending the right examples, but the attahced files may add some
insight.

The examples were intended for demonstration of the timed streaming
features and currently rely on a 1 PPS signal to provide synchronization
across multiple units.

-John

5

Hi John,

Thanks for these examples. I also read that yesterday.
Just want to confirm that:

  1. TDMA engine is only responsible for extract the time from the rx
    samples
    from the USRP resource.
  2. The burst gate block schedules the time for the tx samples.

Are they correct?

On Mon, Feb 4, 2013 at 11:20 AM, John M.
[email protected]wrote:

-John

For the transmitter, it seems that this tdma_engine works like a
and it is different block which means different thread.

Dreams can come true just believe.

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–

Alex,
Dreams can come true just believe.

6

Maybe I have misunderstanding on tdma_engine. Does it only handle the
incoming samples from the usrp source, which means rx samples? I really
want to figure out how the tdma transmitter works.

On Mon, Feb 4, 2013 at 9:45 AM, Josh B. [email protected] wrote:

than the time_transmit_start.

–

Alex,
Dreams can come true just believe.