Date: Sat, 18 Mar 1995 01:50:51 +0200 From: Heikki Suonsivu <hsu@cs.hut.fi> To: terry@cs.weber.edu (Terry Lambert) Cc: freebsd-questions@freefall.cdrom.com Subject: Re: Frame Relay.. Message-ID: <199503172350.BAA27934@shadows.cs.hut.fi> In-Reply-To: terry@cs.weber.edu's message of 17 Mar 1995 20:32:18 %2B0200
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> Frame Relay demands synchronous serial ports..Is there outside
> any commercial available synchronous serial card???
The AppleTalk and TOPS networking software for PCs uses Zilog
UARTS like those found in Sun serial ports. These are capable of
doing sync I/O and some can be had for quite cheap.
No wonder, the junk they are. The chip can only interrupt when either the
first character of a frame arrives, for each character or on a buffer
overrun. For each packet, you need to set up DMA transfer quickly before
you loose any data, as there is no chaining or ring buffering. Appletalk
and other 8530 cards don't usually do DMA bidirectionally, if at all (it is
difficult, unless one wants to hog two DMA channels for each connection).
This is fine for Tetris-loaders like DOS as busy-looping is not an issue,
but hardly a good idea for operating systems.
Digiware in Finland is prototyping a board which also might be of interest,
contact kate@digiw.fi. Its based on motorola communications chip (built
around 68k).
Cyclades and Cronyx have got synch cards but they only spec up to 256k.
There is a 64570 based board available from SDL Communications, or, was
available for about a year ago. I haven't got any experience with these.
The driver needed cleanup but apparently has been in production use. It is
a bit pricey, though, but has got two ports (64570 has two channels). The
chip can max at 7.1 Mbps according to the manual and does chaining to avoid
DMA startup problems.
The address I got is
> SDL Communications Inc.
> 46 Eastman Street
> Easton, MA 02334-1303
> Phone: 508-238-4490
> FAX: 508-238-1053
> Contact: Robbie Dhillon
I have got a driver for NetBSD 0.9 received from Ken Robinson
<robinson@nrnsinc.on.ca>, but I didn't obtain an SDL card and thus never
looked at the driver more intensively than glancing around. The driver
went through freebsd-questions in last october.
Cheap ethernet bridges are popping around and might seem to be a kludge
solution for this kind of problems. I'm testing a pair in week or so. It
needs prioritizing the traffic before sending it over the pridges (there is
a group working at HUT to add IP prioritizing into FreeBSD 2, currently in
early prototype-stage).
I'm interested on any other pointers.
--
Heikki Suonsivu, T{ysikuu 10 C 83/02210 Espoo/FINLAND,
hsu@cs.hut.fi home +358-0-8031121 work -4513377 fax -4555276 riippu SN
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