|
From: Jeff W. <jef...@nt...> - 2014-12-18 21:36:55
|
On 12/18/2014 08:49 AM, Gilles Chanteperdrix wrote: > On Thu, Dec 18, 2014 at 08:35:32AM -0600, Jeff Webb wrote: >> On 12/17/2014 04:31 AM, Gilles Chanteperdrix wrote: >>> On Tue, Dec 16, 2014 at 03:51:16PM -0600, Jeff Webb wrote: >>>> I am using rtnet without rtmac/tdma. I previously sent a patch >>>> that allows one to use the "rtnet" script and rtnet.conf in this >>>> configuration. I would also like to be able to specify a list of >>>> IP addresses in rtnet.conf that are passed along to "rtroute >>>> solicit". I have attached patches for the rtnet and >>>> xenomai-3.git/next repositories. I think others will find them >>>> useful. >>> >>> Well, you should probably be using "nomac" if you are not interested >>> in tdma. >>> >> >> Thank you for your response. I appreciate your advice, Gilles, and >> even more so, since I am new to RTnet. I am somewhat confused by >> the rtmac/nomac configuration, since I haven't found a lot of >> documentation on it. Something I read indicated that the primary >> purpose was for use as skeleton when writing new MAC >> implementations, but it also seems that it is useful for other >> purposes. I have a couple questions that might clarify things for >> me a bit. >> >> There are a couple of ASCII-art drawings at the beginning of the >> README.rtmac file in the rtnet documentation. The first one seems >> to indicate that rtnet can be used without rtmac, if all >> communication is done from RT applications. I see that with rtmac >> inserted, standard linux programs can also send information over >> the real-time interface. The RTmac.spec document indicates that >> the rtmac layer wraps data sent through rtmac with an rtmac frame >> header, and specifies how the non-real-time packets can be >> tunneled through a real-time network. My first question is: does >> the rtmac/nomac configuration still add the rtmac header? I >> assumed the answer was "yes", but perhaps I am wrong. > > The answer is yes, but only for the packets sent from non real-time > applications. The UDP packets sent using RTnet sockets are plain IP > packets compatible with normal IP stacks. > >> >> My initial RTnet application is to send UDP packets in real-time >> to a hardware device manufactured by someone else. Since I am not >> in control of the receiving device, I cannot have any additional >> headers added to my packets. Can I do this without the rtmac >> module inserted? Can I do this with rtmac and nomac inserted? If >> so, what would be the advantage in my application? At some point I >> may need to send/receive TCP and UDP packets for non-real-time >> configuration purposes, but I don't see any need to communicate >> from standard linux programs at this time. >> >> Thank you again to everyone for their input. The documentation is >> not very clear on how (or even if) rtnet can be used to do what I >> need. > > To be able to send plain IP packets using Linux sockets without the > rtmac tunneling, you can use rtnetproxy. The problem with rtnetproxy > is that it creates only one linux interface, and then routing is > done by rtnet. While it may be sufficient for typical applications, > it is insufficient for network oriented equipments which need > NAT, or per-interface QOS settings. > > A solution to this need is to create, like rtmac does, one linux > interface by rtnet interface, but do not do the tunneling that rtmac > does. A long time ago, when I worked for a company which was using > RTnet, I did exactly that, modifying the nomac policy, but the > patches did not went far into rtnet (you can probably find them in > rtnet archives though). > > My plan is to do the same thing, but adding a new mac policy which > would be dubbed xmac (like cross-mac) in xenomai 3 tree. I can not > make any promise on that though, since I have plenty to do already > with rtnet, as I have posted. Ideally, what I would like to do, is > to have, for each NIC, one RT interface which gives good latencies, > and a plain linux interface which allows high throughput. > Thanks, Gilles. That explanation helps a lot. -Jeff |
