Hello Dario,
We are creating a RFNoC block that inputs a continuous flow of data and
> needs to output an irregular burst of variable length.
>
> I tried to research a bit but didn’t found a final answer on the following
> questions:
>
>1. Packets to and from RFNoC blocks need to have a min/max/fixed
>length? Apparently not and if I didn’t misunderstand it is also possible to
>send packets without the length so that their length could be variable but
>just want to be sure
>
> If what you mean is that you might not have to deal with packet length in
your code... Then it is possible. Because the axi wrapper is the one who
forms packets for you, and it will calculate the length for you as well. As
long as you use axi stream with tlast correctly, you won't have to care
about packet length. Your code will only see axi going in and coming out.
About variable packet sizes within the same code from the host can mess up
a lot of things. The rfnoc infra might be supporting that. But some blocks
don't. Like the DDC or the DUC blocks. So if you use them with your block,
it just wont work.
Is there any timing related requirement on when packets are sent/received?
It's not clear what you mean by "timing" here exactly. Your design should
meet FPGA timing, and that is an implementation requirement in order to
avoid undefined behavior. If you are asking about "timed commands", then it
depends on your application. If you need synchronized channels, then you
required timed commands, for example.
My output port would basically resemble a message port… I seem to
> understand that there is some work in progress to support message outputs
> from RFNoC blocks but didn’t really understand if this is really feasible
> or not. If it is where can I find some examples?
>
There are some implementations that have done something alike to a message
port [1]. However, message ports are *not* supported yet in the RFNoC
framework, although there are plans to implement this feature. You might
want to check how rfnoc-fosphor has an alike implementation with the
method rfnoc_fosphor_c_impl::handle_cfg_message, which could be helpful for
what you want to achieve.
The code for rfnoc-fosphor can be found within gr-ettus [2]
On the host side I need to add some custom C code so was looking for the
> tutorial here (http://gnuradio.org/redmine/projects/gnuradio/wiki/Guided_
> Tutorials) but this link does not seem to work anymore and on git there
> seem to be no trace of it. is there any sample skeleton with the block
> implementation to just manage data from a stream and read/write registers?
You might be better off with the RFNoC development guided tutorial here
[3].
Regards,
- Nicolas
[1] https://archive.fosdem.org/2015/schedule/event/rfnocfosphor/
[2] https://github.com/EttusResearch/gr-ettus
[3] https://kb.ettus.com/Getting_Started_with_RFNoC_Development
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