Subject: Re: Support for 16650?
To: None <port-i386@netbsd.org>
From: Thor Lancelot Simon <tls@rek.tjls.com>
List: port-i386
Date: 09/29/2000 22:36:10
On Fri, Sep 29, 2000 at 04:30:30AM +0000, Geoff Wing wrote:
> Gregg C Levine <hansolofalcon@worldnet.att.net> typed:
> :Hello again from Gregg C Levine usually with Jedi Knight Computers
> :I suppose it is too much to ask, if you saw my message? The part may indeed be
> :genuine, but the board design may not be. Let us wait and see if Kevin P. Neal
> :takes my advice.
> 
> Yes, however it's not entirely correct.
> 
> The NS16450 has a 1 byte memory space.  (The 8250 is similar to this)
> The NS16550 has a 16 byte buffer.
> The NS16650 has a 32 byte buffer.
> The NS16750 has a 64 byte buffer.
> The NS16950 has a 128 byte buffer (and external clocking).

That's not correct.

The 16650 is a StarTech (now "Exan" or something like that) part.  They
also make the 16850, which is like a 16650 with some more useful features.
Both have automatic control of RTS/CTS triggered by a threshold FIFO level,
which is a major, major win at high speeds.  These require some special
support in the driver, and I'm not personally convinced that the 16650 
support in our "com" driver actually DTRT at the moment (it did once).

Without that support, the parts act like a 16550 with a "magic" FIFO that
just gives you twice as much depth as you expected so you're less likely
to drop characters.

Different members of the 16[68]50 family have different amounts of FIFO
per-channel.  IIRC, the 1- and 2- channel parts have 32 bytes per channel,
and the 4- and 5- channel parts have 64 bytes per channel, probably on the
reasonable assumption that if you're doing that much I/O through what are
still pretty dumb serial controllers, you're going to need a lot of 
buffering.

The 16570 is a different beast made, as I recall, by TI.  It's not
compatible with the StarTech parts, though it does offer the same basic
features implemented differently.  IIRC all variants of the 16750 have
64 bytes of FIFO per channel.  The 16750 isn't very popular and may not
be in production any more.