brian@ucsd.EDU (Brian Kantor) (06/10/88)
I'm in the process of porting Xinu V7 to an 80186-based network controller - the SANDPAC PS-186. This is a fast little board designed to be a dedicated network controller for the Amateur Packet Radio Network. It has four serial channels capable of running async or HDLC at up to 1 Mbit/S each simultaneously, 256K of static battery-backed RAM, and some other nifty things related to its intended purpose as an automated unattended radio-system controller (probably living in some weatherproof box on a snow-covered mountaintop). The architecture doesn't look much like a PC or AT - the interrupt controller and DMA are QUITE different - and there's no console nor keyboard. The timers, time-of-day clock, and parallel ports are different too. We couldn't have kept the hardware the same as a PC or AT and still gotten the kind of performance out of it that we need. Oh, it does have an NCR SCSI controller, so it IS possible to attach a hard drive controller to it (a DTC or Xebec are available here), but the final system will probably be loaded from EPROM - or uploaded over the radio network link by a simple loader in EPROM, since ordinary disks won't take the environment. I've started by using as much of the V7 Xinu as seems to port directly, and grabbing large pieces of the V6 8086 Intel-board port. The intent is to have a box that is a very efficient IP switch that knows how to do ARP, speak AX.25 over HDLC (that's the legally-required radio networking protocol) and to provide some services like Telnet. As you might guess, I've never ported something quite this large before, and I'd like to reduce the amount of error in the inevitable trial-and-error part. It would help if it weren't quite such a trial, too. I'd appreciate any suggestions on methods of attack. Clearly the first thing to do is get some of the very low-level kernel stuff working - I've already got kputc and kprintf working. I suspect that interrupt handling is next. I'm told we may have an 80186 in-circuit emulator available in a few months, but that's not certain yet. I'd also like to know what the restrictions would be on giving away copies of the software when it's all working. Brian Kantor WB6CYT UC San Diego brian@ucsd.edu
comer@PURDUE.EDU (Douglas Comer) (06/10/88)
Brian, You're off to a good start with kprintf and kputc. The rest of the advice is common sense: add one device driver at a time, testing as you go. Lot's of people boot Xinu from ROM or upload it, so that shouldn't be a problem. You might be able to squeeze it into EPROM (V7 on the LSI fits into 56K bytes, and that includes data, bss, and stack). As for giving it away, that's fine. You can even charge for a product that contains Xinu as long as you charge only for the other parts and not for Xinu itself. Is the SANDPAC board generally available? How much does it cost? What speed will the radio links support? Regards, Doug
brian@UCSD.EDU (Brian Kantor) (06/10/88)
I'm told that the SANDPAC board will be marketed in kit form for something around $200 or so by the Tucson Amateur Packet Radio group, and in some fully-assembled version (probably around $500 or so) by a ham radio manufacturer. It's primarily aimed at the ham radio market, but every other ham packet radio product has been snapped up by non-ham users, so I wouldn't be surprised if that happened with this one too. I have one of 10 prototypes. The others are out at various places around the country where similarly demented people such as myself are porting things to it: other kinds of networking code, such as the Net/Rom product (a proprietary datagram forwarding system); and Phil Karn at Bellcore has one he's playing tcp/ip with. I'm told that the board has also been made to run some version of MS-DOS (ecch). The radio link speed is limited by legal bandwidth restrictions for the most part. 1200 bps is by far most widely used, since with inexpensive modems it occupies about the same radio bandwidth as a voice signal and so is well tolerated by the other users of the ham bands. 9600 bps is used in some less-dense areas of the ham bands. A prototype 56Kbit radio modem is available from some experimenters in Florida for about $200 or so in partial-kit form, but you have to add about $500 of parts and radio to complete that. More information on the SANDPAC PS-186 board is probably available from the developers (write to mike@net1.ucsd.edu). A paper discussing the hardware design issues was published in the 6th ARRL Computer Networking Conference Proceedings, available for under $20 from the American Radio Relay League in Newington, Connecticut, or at large ham radio stores in your hometown. Those Proceedings and earlier ones also present the evolution of digital communications in the ham radio field, and might be interesting reading. There is also a USENET newsgroup and corresponding Internet mailing list for ham packet radio topics. Thanks for the advice! - Brian