From spl(9):

     splhigh()        blocks all hard and soft interrupts.  It is used for
                      code that cannot tolerate any interrupts, like
                      hardware context switching code and the ddb(4)
                      in-kernel debugger.

     splserial()      blocks hard interrupts from serial interfaces.  Code
                      running at this level may not access the tty
                      subsystem.

From sys/arch/i386/include/intr.h (and other similiar):

#define IPL_HIGH        1       /* everything */
#define IPL_SERIAL      0       /* serial */

Which is correct?

Regards,

David Querbach
Real-Time Systems Inc.