[OpenBIOS] serial console

[Dean Gaudet]

On Thu, 19 Feb 1998, Benjamin Scott wrote:

>   Oh, I agree the need for a serial console in some for exists.  But
> consider: Such server farms are pretty much going to be running either
> some flavor of Windows, some flavor of Unix, or Novell Netware.  Windows
> is out, as it *requires* GUI.  Unix (Linux and BSD) should be able to
> use a serial console without any sort of goofy video emulation
> hardware.  That leaves Netware as the only benificiary of such a
> hardware-based product, and I can't say I see a big demand for it.  :-)

No, the linux serial console requires linux to be running.  I want a
serial console the most when the operating system *isn't* running.

>   I covered the software above.  Do we actually know how much hardware
> writes directly to video memory?  I know of some stuff that uses BIOS
> calls for the very reason of compatability; BIOS is guarenteed to be
> there.  If your SCSI card's (or whatever) BIOS is well-behaved, it isn't
> a problem.

Grab a buslogic or adaptec scsi card and watch them put up full screen
menus from their bios.

>   While you can't respond *directly* to such activity, you could run a
> timer loop that checks the video memory emulation region for changes
> periodically and refreshes the VT screen every so often.  Good old DOS
> DOORWAY did something very like that.  And you would only need to do
> this if you have hardware that ignores BIOS and writes directly to
> memory.

It's trivial to map the display itself, yes.  But what you can't do this
way is react to vga register writes.

There's nothing critical about using vga though, the card could emulate
hercules.

>   Much cheaper, though.  :)

But doesn't solve the problem.  It's not reliable, so you can't really
trust it to pull you out of critical situations. 

>   The RESET button works for me.  :)  Now, if you don't want to go over
> and press the button on the system, then yes, things are more
> difficult.  Your serial-console card could include a remote way to reset
> the machine.  The BIOS alone can't do that.  But I think it would be
> cheaper to run a long length of twin-lead wire to the reset-switch
> connector on the mainboard then design and manufacture a whole new
> hardware product.  :-)

What if the system is 60? 100? 600? 1000? miles away from you?

>   Yes, Sun has many advantages over the PC.  As does SGI, DEC, HP, and
> the like.  The primary advantage of the PC has always been *cost*.  And
> special hardware defeats that goal.  :-)

Not really.  In truth you could do most of what I've suggested so far with
a UART, and some lead that lets you trigger SMI.  If you can get yourself
into SMM then you don't need to have anything special on the card.  Once
in SMM the bios has complete control of the system... which leads to
software solutions. 

That gets you remote console for reboots, and for unix once its booted. 
But it still doesn't get you support for scsi cards which do direct screen
writes.

Dean



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