chari@nueces.UUCP (Chris Whatley) (04/24/89)
What is this that I read in the manual about the serial ports "suffering" overruns at 9600 baud or higher? Is this a software problem or a hard ware problem? I thought this machine was supposed to have good IO? I really want to stick a trailblazer+ on this thing now since the DSP-modem does not seem to be destined to exist. I suppose that two trailblazer+'s is out of the question. (You see I'm not fortunate enough to be directly connected to an ethernet) Is this common? I believe the Sun386i had similar input problems on its serial ports too. Why can I run my macintosh serial ports at 56,000 baud? (A macintosh plus to be exact) If I have misinterpreted the info in the library, then please ignore. Chris -- Chris Whatley | "dish... crab fingers... !bigtex!nueces!chari@cs.utexas.edu | dish of crab fingers..." chari@walt.cc.utexas.edu | 1607 Nueces,Austin TX 78723 - 512/453-4238 | (that'll teach you)
wtm@neoucom.UUCP (Bill Mayhew) (04/25/89)
I find it somewhat surprising that the Next has problems at 9600 baud and/or above. It is my understanding that the serial I/O for the two ports on the back is handled by a Zilog 8530 (or second sourced by AMD I think). That chip should be perfectly capable of dealing with it. Sounds like the driver needs some work. Maybe they are using an interrupt per character mode. Such programming would make a couple of context switches per character received. I've seen drivers on other Unix systems with similar problems, Sun systems for instance. I don't know too much about the Next's heart of mach, but I was under the impression that mach's forte is supposed to be dealing with quasi real-time environments. Hopefully, this will be fixed by the time 1.0 hits the streets indeed. There is no excuse for the Next not to be able to cut the mustard with the serial port. My Unix PC (10 MHz 68010) has an 8274 serial controller, which is similar to the 8530, and my Unix PC can achieve a sustained throughput of ~1400 char/sec when running uucp over a trailblazer modem. The 8274 is desinged to optionally implement DMA, but must be used with an external address generator; I don't think that was done in the Unix PC. By the way, can the Macintosh receive a steady stream of data at 56 kb/s? It is prettty hard to do that without a 2-port ram buffer or a DMA channel from the serial port .. or else shut the system down to all other operations while receiving. At that rate you start running up against interrupt latency problems if you don't. Bill wtm@impulse.UUCP