Re: [Discuss-gnuradio] Message passing as input and output in block (C++ coding)

[Jose Torres Diaz]

Hi Josh, 

I've checked this information and it is very useful. I've solved several issues that I had before. However, it is still complaining when I post a BLOB_METADATA (which is a pmt_list) downstream. What I have is the following:

BLOCK 1  --- > BLOCK 2 (both blocks use message passing as blobs)

In BLOCK 1 (work function):

 while (_offset == 0){
         _msg = this->pop_msg_queue(); //Reading the incoming blob
           if (pmt::pmt_is_blob(_msg.value))
         {
         std::cout << std::endl << "found a blob in BLOCK 1" << std::endl;
         break; }
       }
       if (pmt::pmt_blob_length(_msg.value) == 0)
     {
     std::cout << std::endl << "empty blob in BLOCK 1" << std::endl;
     return -1;}    

    pmt::pmt_t BLOB_METADATA = pmt_list3(blob_key,blob_key2,blob_key3);
    //For debugging
    std::cout << std::endl << "Making a list" << std::endl;
    std::cout << std::endl << "this is the list:" <<BLOB_METADATA<< std::endl;

     this->post_msg(0,BLOB_METADATA,_msg.value,_id);  //BLOB_METADATA is a list


In BLOCK 2 (work function):

 while (_offset == 0){
        _msg = this->pop_msg_queue(); //Reading the incoming blob
             if (pmt::pmt_is_blob(_msg.value)) 
           {
         std::cout << std::endl << "found a blob in -BLOCK 2" << std::endl;
         break; }
    }
         if (pmt::pmt_blob_length(_msg.value) == 0) 
       {
         std::cout << std::endl << "empty blob in BLOCK 2" << std::endl;
         return -1;} //empty blob, we are done here

this->post_msg(0,_msg); //Pass the message as it is

//For debugging
     std::cout << std::endl << "posting a message downstream" << std::endl;
     std::cout << std::endl << "DEBUG FROM BLOB TO BLOB 10/10" << std::endl;
     std::cout << boost::format("value previous block=%8d, id previous block=%16s ")
     %_msg.value
     %_msg.srcid

I'm passing a message from BLOCK 1 to BLOCK 2, then I changed the key value and I replaced it as a list (BLOB_METADATA). Everything is running, but it seems to be that the message is not passed from BLOCK 1 to BLOCK 2, here is my errors in GNU Radio Companion:

thread[thread-per-block[8]: <gr_block msg_sourcer (9)>]: gr_block_detail::add_item_tag key: wrong_type : (st2_uplink burst_start_key burst_bb_gain)

Note: st2_uplink burst_start_key burst_bb_gain is the value inside blob1, blob2 and blob3 in the list

Is there any restrictions passing a pmt_list from one block to another?, or is there any constraint when I read the incoming blob from BLOCK 1 into BLOCK 2?.

Thanks a lot for your help, 

Regards, 

Jose

On Wed, Oct 10, 2012 at 9:14 AM, Josh Blum <address@hidden> wrote:

> I generated the BLOB_METADATA as pmt::pmt_t type. However, I cannot post
> blob_data because is related to _msg (in the previous example), which is a
> gr_tag_t type.
>

There are two post_msg methods. The key/value version of the method is a
convenience method that makes a gr_tag_t and sets key and value

https://github.com/guruofquality/grextras/blob/master/include/gnuradio/block.h#L208

> If a copy this blob for example to a new blob as you suggested previously,
> can I then post using: this->post_msg(0, BLOB_METADATA,blob_data, _id); ?.
> I mean, will it change to pmt_t type?.

The value parameter has to be type pmt::pmt_t

There is a function to create a blob from ptr and length:
http://gnuradio.org/cgit/gnuradio.git/tree/gruel/src/include/gruel/pmt.h#n330

-josh