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     npx — Numeric Processing Extension coprocessor


     device npx"nexus"


     The npx 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 npx 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:

     1.   cpu I586_CPU is an option
     2.   the CPU is an i586 (perhaps not a Pentium)
     3.   the probe for npx0 succeeds
     4.   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 hints works correctly (the optimizations are not used until later in the
     bootstrap when npx0 is attached).


     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.