[OpenBIOS] serial console

[Dean Gaudet]

On Thu, 19 Feb 1998, Benjamin Scott wrote:

> Dean Gaudet wrote:
> > The best idea I've ever heard for a serial console on a PC is an ISA video
> > card that behaves like text-mode VGA only,
> 
>   While it would be a good idea, it has two problems: Cost and kludge. 
> Such a thing is going to cost a good amount of bucks, being so rare, and
> it really is a kludge to support weirdness on IBM-PCs.

rare?  Every PC in use at any ISP that has any sense could use one of
these.  Consider the current situation -- in order to have a farm of
machines you need to use expensive video/keyboard multiplexing devices or
deal with the pain of switching cables all the time.  Plus you have no
remote administration of your machines -- telnet doesn't count, it's only
useful when the system is in multiuser mode. 

> > Remember that ISA/PCI cards have bioses on them, and those bioses expect
> > to play with a video card.
> 
>   I have seen a system boot headless (no video at all), but yes, most
> software and some hardware expects to be able to play with video
> memory.

booting isn't what it's all about.  What if during the boot your scsi card
gave you a diagnostic?  It'd sure be nice to see the diagnostic. 

> One solution is to just not use (or fix) such
> hardware/software.

Good luck. 

> Another is a software version of your above serial
> console card.  Hardware and software doesn't really want to talk to a
> video card, just be able to write directly to video memory (and maybe
> play with a couple of video registers).  I am fairly sure we can create
> a region of "video memory" from the BIOS for such stuff.  We could then
> either attempt to convert it to serial, or just ignore it, depending on
> specific needs.  The video registers I'm not sure about; can we hack
> together an emulator for them using just BIOS code, or do we need actual
> hardware?

Won't work.  Your VGA emulation needs to react to reads and writes.  You
"can't" do that -- ok I lie.  If you build your system so that it goes
into protected mode, and then do a v86 emulation to totally fake out the
bios then you can do it.  But you still won't be as solid as a hardware
card. 

> > Plus you've got a more reliable method of generating an NMI/reboot which
> > you'll absolutely need.
> 
>   Why?

Without reboot control remote administration is useless.  The serial ports
on a PC have no way of generating an NMI (or an SMI), so you have no way
of ensuring that the system is recoverable from a kernel failure. 

If you haven't done it before, try administrating a sun box over serial. 
Enjoy the ability to halt and reboot the system, to upgrade the kernel
without fear, to even reinstall the system completely without being at the
physical console.  sun's serial ports and boot prom are designed to be
able to control the system -- a break will send the equivalent of an NMI
and bop you into the prom, from anywhere.  PCs do not have this luxury. 

Granted there are probably some easy hardware hacks that would let you
trigger an NMI (or better yet, an SMI) in response to a serial event.

Dean




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