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

[Bruce Evans]

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