> Other than the responses you've already gotten, likely you'll need to
> compile with -march=r3900(or -mcpu=r3900 if it's an old toolchain) since
> the 3900 is missing a couple of r3000 instructions iirc.
The 3900 family should run MIPS I code compiled for the R3000.
> If it's the 3912 I remember it also doesn't have an fpu, but I could be
> wrong there. If it is, then you need -msoft-float as well.
The 3912 has no FPU, but if you're running on any contemporary
MIPS/Linux kernel and library system, you neither need nor want
soft-float. The kernel does FP instruction emulation. Running soft-float
would make for faster, if larger, code, but requires that the whole
system, particularly glibc, be built for soft-float, which is rarely done
(and the last time I tried it, didin't quite work with the standard
glibc sources out-of-the-box).