jbn@wdl1.UUCP (07/10/84)
We have had full IP/TCP via Ethernet on a PDP 11/70 since the beginning of this year, but we run System V with our own version of 3COM's UNET package using a 3COM Ethernet board. It works quite well for us (Internet host FORD-WDL2.ARPA is such a machine) but there are a few things to watch for if you are bringing up something using that board. 1. You have to modify the PDP 11/70's MMU board with a soldering iron! 3COM provides instructions on how to do this. Still, many sites may not want to. The problem is that the Ethernet board provides memory on the UNIBUS, a concept foreign to the PDP 11/70, and so one must change some jumpers on the MMU board to allow the CPU to address addresses below the top 4K of the UNIBUS address space. 2. You need a good copy routine to copy the data to and from the Ethernet board's memory, out in high physical address space, and there is a nice convenient assembler routine in UNIX system V for doing exactly that, which has a nice little hole where it momentarily releases interrupt lockout while ineptly manipulating the PS. This has been reported to AT&T, which proposes to fix it in a future release, perhaps. The routine that does this is new in system V, and it follows the UNIX convention of not commenting the assembly code, but the people coding in the kernel nowadays don't seem to be good enough to get away with that. This little gem cost us three months work to find. 3. You have to modify the kernel not to use all the Unibus mapping registers so that it doesn't try to use the space you took away to allow the Ethernet controller memory to occupy UNIBUS address space. There isn't a problem with UNIBUS contention with this card, since it is shared-memory, not DMA, and the processor requests are of course preempted by the NPR requests. But the Interlan card probably integrates more easily into UNIX, being a DMA card, which both UNIX and the PDP 11/70 understand better. On VAXen, both ways work fine, by the way. We still need a PTY handler for system V, preferably a 4.1BSD conversion. Anybody have one?