how to use the floating point hardware in nios II custom instructions

thank you very much!

when i change the system.h file, the objdump file becomes:

c=a*b;

1082c0: e13ffd17 ldw r4,-12(fp)

1082c4: e17ffe17 ldw r5,-8(fp)

1082c8: 01083c00 call 1083c0 <__mulsf3>

1082cc: 1007883a mov r3,r2

1082d0: e0ffff15 stw r3,-4(fp)

c=ALT_CI_NIOS_CUSTOM_INSTR_FLOATING_POINT_0(0,b,a); //*

10832c: e0bffe17 ldw r2,-8(fp)

108330: e0fffd17 ldw r3,-12(fp)

108334: 10c5ff32 custom 252,r2,r2,r3

108338: e0bfff15 stw r2,-4(fp)

and the c=ALT_CI_NIOS_CUSTOM_INSTR_FLOATING_POINT_0(0,b,a); return the right result, and the calc time is much lesss than the c=a*b

how do you know to change the inii to fnff in system.h file?

i am new to altera and nios, i want to learn more.

it seems like my project still has some problems, but at least i know how to use the floating point hardware in nios II custom instructions

but i still do not understand why the system.h in my project have to change manually? and why i can not use c=a*b.

may be i can try floating point hardware2.

thanks again!