Re: [Discuss-gnuradio] RTOS and GNU Radio

[Jane Chen]

Hi all,


Eric, thank you for your reply.
I ran the tunnel.py with the username "useSDR"  in group usrp and added
@usrp  - rtprio 50 in the  /etc/security/limits.conf.   gr.enable_realtime_scheduling() is in the orignial tunnel.py file.

However, I keep get an error as following:

File "tunnel_original.py", line 78, in open_tun_interface
    tun = os.open(tun_device_filename, os.O_RDWR)
OSError: [Errno 13] Permission denied: '/dev/net/tun'

I think it is because I did not set the authority right on my linux system.


I have tried many ways. I even set "root" in the group usrp.  The RTT of tunnel.py is still about 30 ms.

/etc/group
root:x:0:root,useSDR
usrp:x:501:useSDR,root


Does anyone have any idea what's wrong?


Thank you,
Jane

--- On Wed, 8/12/09, Eric Blossom <address@hidden> wrote:

From: Eric Blossom <address@hidden>
Subject: Re: [Discuss-gnuradio] RTOS and GNU Radio
To: "Jane Chen" <address@hidden>
Cc: address@hidden
Date: Wednesday, August 12, 2009, 6:20 PM

On Wed, Aug 12, 2009 at 11:05:19AM -0700, Jane Chen wrote:
> Hi all,
>  
> I ran the  tunnel.py, which is one of the gnuradio-examples, on two
> PCs (fedora 9 (kernel: 2.6.27), GNU Radio 3.2 and Intel Pentium
> D). The RTT is about 30ms. I read the paper "Enabling MAC Protocol
> Implementations on Software-Defined Radios" which is written by
> George Nychis and found that GNU radio needs 25ms in the user space
> in the example. I am wondering if I can use the real time OS to
> reduce the latency in the user space. However, I don't see any RTOS
> in the build guide on the GNU Radio Wiki
> (http://gnuradio.org/trac/wiki/BuildGuide ) . Does anyone know about
> if RTOS can reduce the RTT of tunnel.py to less than 1ms?

Before you go the RTOS route, I suggest that you simply try enabling
real-time scheduling on Linux.

Be sure you're in group usrp, then add this line to
/etc/security/limits.conf:

@usrp  - rtprio 50


Then in your GR program add a call to:

  gr.enable_realtime_scheduling()

There are several examples that do this.

Eric