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Altera_Forum
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10 years ago

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

hi i want to compare the speed difference of floating point calc between custom instruction floating point and software. this is my code:# include <stdio.h># include <altera_avalon_pio_regs....
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
10 years ago

That is very weird. With floating-point hardware inserted and BSP re-generated, c=b*a should directly infer "custom 252". Can you try to delete BSP and create a new one?

I tried c=ALT_CI_NIOS_CUSTOM_INSTR_FLOATING_POINT_0(0,b,a) ;, it gives me 0.0 as well. I am curious why there is the additional fixsfsi. It is trying to convert single precision to integer operation, which could mess the operation up.

2f0: 00003900 call 390 <__fixsfsi>

2f4: 9009883a mov r4,r18

2f8: 1023883a mov r17,r2

2fc: 00003900 call 390 <__fixsfsi>

What version of Quartus are you using? I tried 14.1/15.0 works for me,