misc/74786: Smartlink Modem causes interrupt storm onRELENG_4 and RELENG_5

[Bruce Evans]

The following reply was made to PR kern/74786; it has been noted by GNATS.

From: Bruce Evans <bde at zeta.org.au>
To: Mike Tancsa <mike at sentex.net>
Cc: freebsd-gnats-submit at freebsd.org, freebsd-bugs at freebsd.org
Subject: Re: misc/74786: Smartlink Modem causes interrupt storm on   RELENG_4
 and RELENG_5
Date: Fri, 10 Dec 2004 11:38:57 +1100 (EST)

 On Wed, 8 Dec 2004, Mike Tancsa wrote:
 
 > At 02:22 AM 08/12/2004, Bruce Evans wrote:
 >
 > >Try this fix.  For the uhci-sio conflict, it should avoid problem (1)
 > >(please try it with the RF_SHAREABLE flag removed so that if this is
 > ....
 > >115200 bps provided the UART is buffered and HZ >= 1000.  With
 > >unbuffered UARTs and HZ = 100, only 4800 bos mostly works.
 
 Oops.  "4800 bos" should be "600 bps" (a 1-byte fifo drained 100 times
 per second gives at most 100 cps or 1000 bps; 600 gives a safety margin).
 
 >
 > Note,
 > When removing the RF_SHAREABLE flag from the patch as applied to the
 > default src code for RELENG_5, the modem is not usable.
 
 RELENG_5 stil has a reasonable default for HZ (100) so the maximum cps
 wth a 16-byte fifo is 16 * 100 * 10 = 16000.  I guess you use the default
 and don't use a 2400 bps modem that would work with a max of 16000.
 
 > With RF_SHAREABLE,
 > all *seems* to work with the modem, but I dont have any real tests, other
 > than dialing up and doing a fetch of a large file.
 
 Lost characters would be reported as silo overflows.  Any protocol with
 error handling would recover from a few OK.
 
 Bruce