Subject: Re: Modem Board recommendations for NetBSD - i386
To: None <>
From: Charles M. Hannum <>
List: current-users
Date: 10/28/1999 03:23:30
Thor Lancelot Simon <> writes:

> Try to find one that uses one of the multi-port 16650 chips.  They have
> up to 64 bytes of FIFO per channel and RTS/CTS flow control in hardware;
> this takes a *lot* of load off the CPU by reducing the number of interrupts
> generated, and also eliminates the possibility of dropped characters.

A belated addition to this thread...

Technically, they do not `reduc[e] the number of interrupts', unless
you increase the FIFO threshold for generating an interrupt.  But
doing so in turn limits the possible RTS/CTS threshold, and thus you
don't necessarily get any better protection against FIFO overflows.

Optimizing the combination of interrupt threshold and RTS/CTS
threshold is complicated (and by nature is dynamic, since it's
affected by other interrupt load), and the driver does not currently
attempt to do this.  (Nobody else's does either, AFAIK.)