Path: utzoo!dciem!nrcaer!scs!spl1!ddsw1!bigtex!james From: james@bigtex.uucp (James Van Artsdalen) Newsgroups: comp.unix.microport Subject: Re: serial ports on the '286 Message-ID: <6067@bigtex.uucp> Date: 13 Aug 88 07:32:39 GMT Article-I.D.: bigtex.6067 References: <531@micropen> <4690@b-tech.UUCP> <5909@bigtex.uucp> <532@micropen> Reply-To: james@bigtex.UUCP (James Van Artsdalen) Organization: F.B.N. Software, Austin TX Lines: 34 In article <532@micropen>, dave@micropen (David F. Carlson) wrote: > The PIC (interrupt controller) doesn't "lose" interrupts, it allows them > to be masked long enough that the 1 deep fifo on the 8250 family is overrun. > Further interrupt events while a pending interrupt is still flagged does > nothing to the CPU but the events that they represent are possibly > irrevocably lost. This sounds like a distinction without a difference. I don't care *what* part is responsible for the fact that a character was lost ("overrun", if that's what you wanted). All I know is that a character came, an interrupt was signaled, but the CPU saw neither, and the character was lost. Fiddling with the PIC or using CLI are all the same to a lost character... > But raw mode is defined (often) to return in *less* than 10 characters. Specifically, uucp uses a VMIN of 6 when sending data (70 when receiving). Zmodem defaults to 133. Who knows what kermit does - it probably sets up a committee to decide. :-) > The "win" of the fifo is that overruns are nearly impossible [...] That's what I meant to say. But I also think you underestimate the load that 2000 interrupts/sec (19.2Kbps) places on the system - the kernel is rather slow about interrupts. If you reduce the interrupts by a factor of 10 or VMIN, whichever is less, you'll substantially cut system load. In any program that does sustained high-speed receiving (such as Zmodem or uucp), VMIN is already set greater than 1 to cut the potential load of 2000 read(2) calls per second, which probably the kernel couldn't handle anyway. bigtex appears to be able 30% loaded when uucico talks TB+: I imagine it's worse for the 286s. -- James R. Van Artsdalen ...!uunet!utastro!bigtex!james "Live Free or Die" Home: 512-346-2444 Work: 328-0282; 110 Wild Basin Rd. Ste #230, Austin TX 78746