Copyright (c) 1993 Christopher G. Demetriou
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from: npx.4,v 1.1 1993/08/06 10:58:03 cgd Exp
$FreeBSD: head/share/man/man4/man4.i386/npx.4 90325 2002-02-06 21:42:58Z markm $

.Dd August 28, 1993 .Dt NPX 4 i386 .Os .Sh NAME .Nm npx .Nd Numeric Processing Extension coprocessor and emulator .Sh SYNOPSIS .Cd "device npx" .Cd hint.npx.0.at="nexus" .Cd hint.npx.0.port="0x0F0" .Cd hint.npx.0.flags="0x0" .Cd hint.npx.0.irq="13"

p For hosts without a FPU coprocessor add: .Cd "options MATH_EMULATE" or .Cd "options GPL_MATH_EMULATE" XXX this is awful hackery to get it to work right... -- cgd
What the heck does he mean? - cracauer
.Sh DESCRIPTION The .Nm driver enables the use of the system's Numeric Processing Extension coprocessor, if one is present. Numeric processing extensions are present in systems with .Sy 486DX CPUs and in systems with .Sy 387 or .Sy 487SX coprocessors. The .Nm driver is required for proper system functioning regardless of whether or not a NPX is present.

p If there is no NPX present in the system, the MATH_EMULATE or GPL_MATH_EMULATE option must be defined in the kernel configuration file. It will provide support for the instructions normally executed by the NPX. If there is no NPX in the system and the kernel is not built with math emulation, the system will not boot.

p You can choose to use a much more fully-featured math emulator (under the GPL license) by including the option GPL_MATH_EMULATE in your kernel configuration file instead of the MATH_EMULATE option.

p The .Sy GENERIC kernel configuration uses the MATH_EMULATE option.

p The flags for npx0 are: l -tag -width xxxxxxxxx -compact t 0x01 don't use the npx registers to optimize bcopy. t 0x02 don't use the npx registers to optimize bzero. t 0x04 don't use the npx registers to optimize copyin or copyout. t 0x08 use emulator even if hardware FPU is available. .El

p The npx registers are normally used to optimize copying and zeroing when all of the following conditions are satisfied: l -enum -compact t I586_CPU is an option t the cpu is an i586 (perhaps not a Pentium) t the probe for npx0 succeeds t INT 16 exception handling works. .El Then copying and zeroing using the npx registers is normally 30-100% faster.

p The flags can be used to control cases where it doesn't 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). Flag 0x08 automatically disables the i586 optimized routines. .Sh CAVEATS The emulator is much slower than the NPX coprocessor. This will result in poor floating-point math performance if the emulator must be used.

p The non-GPL emulator does not support the whole set of npx instructions. It is sufficient for booting and configuring a system, but it cannot support a system with normal workload unless care is taken to compile the whole system (including third-party packages) with compiler options that avoid the use of the non-emulated instructions. .Sh 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. If this is the case, the emulator must be used if consistent system operation is desired.

p When using the default MATH_EMULATE option, transcendental function instructions are not implemented. Emulation of other instructions is suspect.