Re: [Discuss-gnuradio] Read and Write a PMT input/output GNURadio C++

[Marcus Müller]

Hi Cristian,

you need to subscribe a handler to the message port. See:

https://wiki.gnuradio.org/index.php/Guided_Tutorial_Programming_Topics#5.3.2_Adding_Message_Passing_to_the_Code

It's absolutely up to you what kind of PMT you're publishing over a message port, but it's canonical to have a PMT dict that maps

pmt::mp("propertyname") -> pmt::whateversuitsyourproperty.

As an example, see what the gr-uhd blocks accept [1]

Best regards,

Marcus

[1] https://gnuradio.org/doc/doxygen/page_uhd.html#uhd_command_syntax

On 06/26/2017 07:35 PM, Cristian Rodríguez wrote:

Hi all,

I'm not sure about how to read and write PMT ports from and to local variables. I'm going to expose what i'm doing, and if someone can help me i would be very greatful.

I've created an input and an output of PMT type.

message_port_register_in(pmt::pmt_t in_threshold)

message_port_register_out(pmt::pmt_t out_threshold)

Now i want to read the port, and save the data in a local variable, do operations with that variable, and later write it in the output,

I create the variables,

double d_threshold;
pmt::pmt_t target;

I read it, I don't know how to do it. But I suppose:

message_port_sub(pmt::pmt_t in_threshold,pmt::pmt_t target);

d_threshold= pmt::to_double(target);

And, I think i can write it as follows:

msg=pmt::from_double(d_threshold);

message_port_pub(pmt::pmt_t out_threshold,pmt::pmt_t msg);

What do you think, i've seen several examples, and they do this, message_port_pub(pmt::mp("symbols"), pmt::cons(pmt::make_dict(), pmt::init_c32vector(48, symbols)));
      

But I don't understand why it is necessary to use pmt::make_dict().

Thanks in advance.

Best regards,

Cristian

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