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Date: Sun, 14 Nov 2004 12:11:48 +0200
From: Danny Braniss <danny@cs.huji.ac.il>
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cc: freebsd-hackers@freebsd.org
Subject: Re: boot serial console speed 
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[...]
> This is the value passed in the AL register to the Int 14/AH=3D00h
> BIOS function:
> 
> 	http://www.ctyme.com/intr/rb-0811.htm
> 
> : Bit(s) Description     (Table 00300)
> : 7-5    data rate (110,150,300,600,1200,2400,4800,9600 bps)
> : 4-3    parity (00 or 10 =3D none, 01 =3D odd, 11 =3D even)
> : 2      stop bits (set =3D 2, clear =3D 1)
> : 1-0    data bits (00 =3D 5, 01 =3D 6, 10 =3D 7, 11 =3D 8)
> 
> 0xE3 =3D 111-00-0-11 =3D 9600 bps, no parity, 1 stop bit, 8 data bits
> 
> But I think it's not possible to set it to anything above 9600 bps
> using this BIOS call.

yes, you are probably correct. Assuming then, that if we want speeds above
9600bps,  and assuming that the bios set the bauds correctly,
how about setting BOOT_BOOT0_COMCONSOLE_SPEED=0 and if so
in boot0.S

#if defined(SIO) && COMSPEED != 0
/*
 * Initialize the serial port.  bioscom preserves the driver number in DX.
 */
		movw COMSPEED,%ax		# defined by Makefile
		callw bioscom
#endif