Re: [Discuss-gnuradio] How can I read the value of RSSI?

[George Nychis]

Hi Calogero,

address@hidden wrote:
> Hi,
> the PC receives packets BULK of 512 byte by USB. I have seen the form of packet
> and in several fields there is the field RSSI. 

Do you mean the in-band USB packet?  I think the default USB packet does 
not carry the RSSI.

> I want to read the value of RSSI
> by packets but I don't understand where I can read this value by code C++. Could
> you suggest where I can read this value by files C++?
> Thank you very much.

You're in luck, we have been working on in-band signaling through the 
use of the new m-block which can get you this value in 1 of 2 ways.  But 
you need to checkout the SVN trunk.  It is not in the current GNU Radio 
release:

svn co http://gnuradio.org/svn/gnuradio/trunk

First, build the code.

Then, travel into this directory:
usrp/host/apps-inband

At line 312, there is an if() statement, write this else statement to it:
else {
    if(pmt_t rssi = pmt_dict_ref(properties,
                                 pmt_intern("rssi"),
                                 PMT_NIL)) {
      if(!pmt_eqv(rssi, PMT_NIL) && verbose)
        std::cout << "RSSI: " << rssi << std::endl;
}

One more change at line 104:
"nanocell9.rbf" to "usrp-inband.rbf"

Then, download this file:
http://www.andrew.cmu.edu/user/gnychis/usrp-inband.rbf

...and put it in the appropriate USRP RBF directory, which is usually:
/usr/local/share/usrp/rev2/

Rebuild and:
./test_usrp_inband_rx

... you will see the RSSI field being dumped for every packet you 
receive from the USRP.

Note that you can only use basic TX/RX daughterboards with this code 
currently.

You can use this as a building block for whatever you want to do.  But I 
strongly suggest you read this thread to really understand what RSSI 
value that is:
http://lists.gnu.org/archive/html/discuss-gnuradio/2007-08/msg00085.html

If you really want the 32-bits (if you read the thread, you'll 
understand)... you can use a read_reg command.  We have mapped the RSSI 
register to a local register that you can read from.  But, I'd have to 
look up where we mapped this too, double check that it's still mapped, 
and then you can use this as a building block:
host/apps-inband/test_usrp_inband_registers.cc

Let me know if you want the full 32-bits and I will explain.

- George