The
driver enables the use of the system's Numeric Processing Extension
coprocessor.
Numeric processing extensions are present in
systems with
486DX
CPUs and in systems with
387
or
487SX
coprocessors.
The
driver is required for proper system functioning.
If there is no NPX in the system, the system will not boot.
The flags for
npx0
are:
0x01
do not use the NPX registers to optimize bcopy.
0x02
do not use the NPX registers to optimize bzero.
0x04
do not use the NPX registers to optimize copyin or copyout.
The NPX registers are normally used
to optimize copying and zeroing
when all of the following conditions are satisfied:
cpu I586_CPU
is an option
the CPU is an i586 (perhaps not a Pentium)
the probe for
npx0
succeeds
INT 16 exception handling works.
Then copying and zeroing
using the NPX registers
is normally 30-100% faster.
The flags can be used
to control cases
where it does not work or is slower.
Setting them at boot time
using userconfig works correctly
(the optimizations are not used
until later in the bootstrap
when
npx0
is attached).
BUGS
There are lots of them, especially on old cheap motherboards.
In particular, some motherboards do not have the interrupt lines from
the NPX to the CPU wired properly.
