Messages in this thread | ![/](/images/icornerl.gif) | | From | "Cigol C" <> | Date | Mon, 17 Mar 2003 11:11:52 +0530 | Subject | RE: RS485 communication |
| |
Thannks for the info. Can i acheive IP over RS485 if i use SOCK_PACKET. I need some more info on this if u could provide that. If this option is set in the socket call will i have an option the choose the hardware interface.
----- Original Message ----- From: Chris Fowler Date: 15 Mar 2003 10:42:53 -0500 To: Robert White Subject: RE: RS485 communication
> I think using SOCK_PACKET an an ethernet chip may be the best choice. > You can use IP or you can use RWP (Rober White Protocol). > > > On Sat, 2003-03-15 at 03:07, Robert White wrote: > > Yes, that, but that is only part of it. > > > > The RS485 is a proper bus, so this custom program (or programs) will have to > > act as full bus arbiters and a kind of router. Each PPP daemon must receive > > ONLY the data that its peer daemon transmits. That means that each slave > > must know to ignore the data not destined for it. Further, the master, > > which would have multiple PPP instances running on it, will need to decide > > which of those instances get which of the receiving bytes. > > > > So just like an Ethernet transceiver puts a protocol frame around the data > > to get it to the destination, the transport program will have to put > > envelopes around the data. THEN the master transport program will tell each > > slave when and how many of its envelopes it may send. The only way that can > > work (because there is no "ring" you can't pass a "token") is for the master > > to ask each slave in turn: "Got anything to send?" > > > > This usually devolves to a sequence of "#1, say your piece", "#2 say your > > piece" etc. That is a very bad performance model. > > > > So every frame of data will need to be arbitrarily wide, meaning a length > > code, and will need an in-multiplexor address. > > > > So the master, for instance, will say "slave 1, go". The slave 1 will send > > a packet (not necessarily a PPP packet, as the multiplexor will have > > overhead data etc.) > > > > The master will look at the address and decide which local pty the data is > > for and send it there. (Think a simple byte pump here) > > > > When that pty has response data, and when the master says "slave 0 (e.g. me) > > go" it will frame a message that slave #1 will receive and put through to > > its local pty. Slave 1 also has the job of ignoring data for slaves 2 > > through N and the Master (Slave 0). > > > > In short, he has to write a distributed application that pumps data into and > > out of a broadcast medium, and makes sure that each participant gets only > > the data intended for itself. (This is what both the Ethernet hardware > > layer, and the IP protocols do.) > > > > In communications you almost always put protocols inside of protocols to > > some significant depth. > > > > For instance, when you play Unreal Tournament 2003: > > Unreal Tournament's data is carried by UDP, > > The UDP is carried by IP, > > The IP is carried by the Ethernet hardware access layer (raw Ethernet), > > Those packets may go to your cable modem which either wraps the Ethernet > > hardware packets or decodes them and reencodes the IP into whatever it > > does. > > > > >From there, if your cable modem is doing PPPoE there are even more layers. > > > > This guy will only have to write a multiplexing layer, but it won't be fun. > > > > Then again, the Ethernet people have done all that, which is why it is > > cheaper and easier to just get the Ethernet hardware and use it. > > > > Rob. > > > > -----Original Message----- > > From: Chris Fowler [mailto:cfowler@outpostsentinel.com] > > Sent: Thursday, March 13, 2003 3:31 PM > > To: Robert White > > Cc: Ed Vance; 'Linux PPP'; linux-serial@vger.kernel.org; 'linux-kernel' > > Subject: RE: RS485 communication > > > > > > Are you saying that for him to to use PPPD that he will have to write a > > program that will run on a master and tell all the slave nodes when they > > can transmit their data. In this case it would be ppp data. Hopfully > > in block sizes that are at least the size of the MTU ppp is running. > > > > Chris > > > > > To unsubscribe from this list: send the line "unsubscribe linux-serial" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- ______________________________________________ http://www.indiainfo.com Now with POP3/SMTP access for only US$14.95/yr
Powered by Outblaze - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| ![\](/images/icornerr.gif) |