Serial console only works after reboot?

[Bruce Evans]

On Mon, 5 Jan 2004, Bruce M Simpson wrote:

> On Sun, Jan 04, 2004 at 04:41:03PM -0700, M. Warner Losh wrote:
> > Somewhere along the way, it gets set to 115200.  Maybe it is
> > initialized to 115200 by the boot blocks?  I think once there's a
> > divisor programmed into the serial port, the kernel console code
> > doesn't change it.  I could be wrong about this, however....

sio always uses the current divisor iff:
- the kernel was booted with RB_SERIAL, and
- the current divisor is nonzero.  A divisor of 0 "can't happen", but is
  most likely after a cold boot when everything neglects to set the
  divisor (since the contents of the divisor registers is undefined
  after 8250-16x50 reset).  However, anything that sets RB_SERIAL
  should set the divisor.  sio cannot check that the port that it reads
  the divisor on is the same one that the boot program set RB_SERIAL on.

> Try installing boot0sio as your boot manager. It specifically requests 9600
> 8-N-1 via BIOS calls. However this does mean that boot selection has to
> happen over COM1.

It should use BOOT_COMCONSOLE_PORT and BOOT_CONSOLE_SPEED like boot2
does.  These are standard -- see make.conf(5).  boot2 doesn't use the
BIOS, so BOOT_COMCONSOLE_PORT can be a port not understood by the BIOS.
boot0sio would have problems with this, and mapping BOOT_COMCONSOLE_PORT
to a BIOS port number might take more code than fits.  boot2 also supports
setting the character format (B2SIOFMT macro), but this is nonstandard and
not supported by the sio console.

Bruce