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From: bruce@balilly (Bruce Lilly)
Newsgroups: comp.sys.3b1
Subject: Re: more on the HFC saga
Message-ID: <1991May23.003857.8878@blilly.UUCP>
Date: 23 May 91 00:38:57 GMT
References: <102086@becker.UUCP> <1991May22.041659.13189@fithp>
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Organization: Bruce Lilly, Flushing, NY
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In article <1991May22.041659.13189@fithp> mhw@fithp (Marc Weinstein) writes:
>
>I'm beginning to think that there *ARE* select PCs out there which may
>just be able to handle these higher throughputs.  I know of at least
>one 3b1 which can communicate with a Sun using V.42bis, 19200 port rate,
>and sees ~1800 Bps with no data corruption.  Mine can't do this, and I'm
>not sure what the difference is.  Perhaps the port rate is not exactly
>19200 on some systems - perhaps the CPU clock is just a bit faster.
>
>Anyone care to speculate?

OK (remember, this is speculation, not hard facts): According to the
Device Driver Development Guide, the last driver to be installed has its
interrupt service routine(s) placed at the beginning of the interrupt
"chain". If one is using a combo board, with few other drivers, and if the
cmb driver is last to be installed, it might result in somewhat better
interrupt response than if there are many loadable drivers (particularly
huge ones like the ether driver) with the cmb driver loaded early (so that
its interrupt routine only gets characters after the other routines have
been polled).  I'm not sure how the built-in driver for /dev/tty000 is
linked into the interrupt service chain, but that might be another
pertinent factor.

Other possible factors are the version of the OS, hardware revision
levels, kernel modifications (such as the patch to speed up response to
keyboard input, which might slow down response to tty interrupts), the
number of installed serial boards, the type of serial boards (EIA or
combo).

I've re-ordered the loadable drivers here a few weeks ago to load the cmb
driver last in order to be able to see if that has makes any noticable
difference in handling serial response on the combo boards, but I haven't
had the time to test the response yet.  However, the system has stayed up
since the change, with no noticeable problems:

balilly.UUCP  up 17+02:56,     1 user,   load    0.14,    0.23,    0.16

 DEVNAME  ID  BLK CHAR  LINE   SIZE    ADDR     FLAGS
    wind   0   -1    7   -1  0x9000   0x4d000 ALLOC BOUND 
   ether   1   -1   10   -1 0x13000  0x360000 ALLOC BOUND 
    nipc   2   -1   -1   -1  0x7000  0x373000 ALLOC BOUND 
      xt   3   -1    9    1  0x3000  0x37a000 ALLOC BOUND 
     dup   4   -1   18   -1  0x1000   0x5f000 ALLOC BOUND 
     cmb   5   -1   -1   -1  0x3000  0x37d000 ALLOC BOUND 

-- 
	Bruce Lilly		blilly!balilly!bruce@sonyd1.Broadcast.Sony.COM