# How do I use the Gnuradio GRC XML RPC client or server components? **URL:** \ **Category:** GNU Radio\ **Created:** [April 23, 2015, 5:22am UTC](https://www.ruby-forum.com/t/how-do-i-use-the-gnuradio-grc-xml-rpc-client-or-server-components/241677 "2015-04-23T05:22:34Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\ **Post date:** [April 23, 2015, 5:22am UTC](https://www.ruby-forum.com/t/how-do-i-use-the-gnuradio-grc-xml-rpc-client-or-server-components/241677/1 "2015-04-23T05:22:34Z")
Please understand, I know nothing about networking, client, server, rpc, marshaling, sockets, Python and all newer programming environments. However; I do know C,C++ and understand Windows messaging, wait for single object, wait for multiple objects and similar Windows API stuff. Not sure if there is a counterpart in Linux. I want to use an external program, written in Pascal, running on the same machine and independent from Gnuradio, to control variables on the GRC flow graph. Specifically, I want to control the frequency, gain and more as needed of an Ettus B200 SDR. The Pascal program runs natively, on Ubuntu Linux; it does not require wine or any other Windows emulation. I know this may be difficult, as most examples are scripted in Python. Any help is greatly appreciated. – View this message in context: [http://gnuradio.4.n7.nabble.com/How-do-I-use-the-Gnuradio-GRC-XML-RPC-client-or-server-components-tp53427.html](http://gnuradio.4.n7.nabble.com/How-do-I-use-the-Gnuradio-GRC-XML-RPC-client-or-server-components-tp53427.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![robredford](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/7ea924/32.png) [@robredford](https://www.ruby-forum.com/u/robredford)\ **Post date:** [April 23, 2015, 9:38am UTC](https://www.ruby-forum.com/t/how-do-i-use-the-gnuradio-grc-xml-rpc-client-or-server-components/241677/2 "2015-04-23T09:38:05Z")
Hi numeric, bad news first: considerable amount of work goes into making GNU Radio, which, at its core, is a C++ library, work with python, up to the point that you can actually use python classes inside the GNU Radio framework. The same level of integration won’t (without massive effort) be attainable for pascal. However, the xmlrpc blocks just use standard-conforming XML-RPC calls, so maybe this “official recommendations” document is of interest to you [1]. Now, for almost any language out there exist XML-RPC implementations, I guess – however, if that is the case for Pascal (I guess you’re using freepascal?), I don’t know. Maybe you’ll have to swallow the pill and either write a “Pascal-writes-stuff-into-a-pipe” to XML-RPC converter in your language of choice (in python, that would be but this much code, approximately, untested: #!/usr/bin/python2 import xmlrpclib s = xmlrpclib.Server(‘[http://localhost:8080](http://localhost:8080)’) commanddict = { “frequency”: lambda x: s.set\_freq(float(x)) , “gain”: lambda x: s.set\_gain(float(x)), “taps”: lambda x: s.set\_filtertaps(list(map(float,x.split(“,”)))), “stop”: lambda x: s.stop() } inputfile = open(“/path/to/the/fifo”, “r”) while True: line = inputfile.readline() if line.lower().startswith(“exit”): break command, valuestring = line.split(“:”) #now, get command from dictionary and apply it to string try: commanddictcommand except: #this happens if the command is not in the dict, or something went wrong doing RPC pass # don’t do anything, just wait for the next command Now, of you’ll need to mkfifo /path/to/the/fifo and have your pascal program write lines of the scheme gain:34 taps:1,2,3,4.0 stop:nowtheflowgraphdiesandthiscommandjustneedsaparameter exit to that filename. I assume things are equally easy in C++, but I’ve never tried XML-RPC from C++, and all the string-juggling really gets easy in python, imho. Best regards, Marcus ---
**Author:** ![robredford](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/7ea924/32.png) [@robredford](https://www.ruby-forum.com/u/robredford)\ **Post date:** [April 25, 2015, 8:21am UTC](https://www.ruby-forum.com/t/how-do-i-use-the-gnuradio-grc-xml-rpc-client-or-server-components/241677/3 "2015-04-25T08:21:20Z")
Thank you Marcus for your reply. Yes; to answer your question. The Linux version is Freepascal with the Lazarus IDE. It is very much like Delphi with a useful exception. No BDE (Borland Database Engine) is required. You have given me an idea for a plan to solve my question. If the XMLPRC is a DLL then freepascal can directly import the DLL and gain access to it’s functions. No need to pipe the string to a convertor. Today my USB drive got messed up. I have to re-load Linux, gnuradio and Lazarus to continue the effort. A day or two should complete the restoration; the "BOSS " (not the boss at work) permitting. Rob Marcus Müller-3 wrote > while True: > > to that filename. > > I assume things are equally easy in C++, but I’ve never tried XML-RPC > from C++, and all the string-juggling really gets easy in python, imho. > > Best regards, > Marcus – View this message in context: [http://gnuradio.4.n7.nabble.com/How-do-I-use-the-Gnuradio-GRC-XML-RPC-client-or-server-components-tp53427p53471.html](http://gnuradio.4.n7.nabble.com/How-do-I-use-the-Gnuradio-GRC-XML-RPC-client-or-server-components-tp53427p53471.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com).