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Altera_Forum's avatar
Altera_Forum
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21 years ago

HW Multiplier

Who was the xyz! who took out the hardware multiplier in NIOS2 ???? That person did not think. I know the plan it to use the HW Mult units in CycloneII BUT consider the following.... NIOS is flui...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
21 years ago

Tim

Excellent !!

http://forum.niosforum.com/work2/style_emoticons/<#EMO_DIR#>/biggrin.gif

Only one thing to remember...

I have entered the &#39;overriding&#39; code in one of my SDK (I still using legacy code) libraries and compiled via &#39;make all&#39; in the lib directory.

The thing to remember is to make the function global otherwise the old __mulsi3 will stick like mud on a bumper! 

.global __mulsi3
.type __mulsi3, @function
__mulsi3:
              custom 0,r2,r4,r5
ret

I haven&#39;t done major code benchmarks but I did see serious improvements with the custom instruction.

Be careful of the compiler! It is smart. Don&#39;t just multiply something and then check the speed. Make sure that your code can&#39;t be optimized out into add instructions. Look at your .objdump to see if the code really uses <__mulsi3>.

"Now go forth and multiply..."

Victor