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Honored Contributor

15 years ago

Writting floating point numbers using IOWR IORD

Hi,

I'm trying to read a custom register which has a 32 bit floating point value, from the NIOS in the c-code using the Macro IORD(base,offset).

If I assign this to a variable defined as float and Add it with 2.

And write the result into another custom register using IOWR Macro.

I'm not getting equivalent IEEE-754 value in the register.

Can anybody suggest what might be the problem?

Code is as below:

float x,v;

x= IORD(IOREG_BASE,0); // Reading from the register1 defined in H/W

v= x+2;

IOWR(IOREG_BASE,1,v); // Writing to register2 defined in H/W

11 Replies

Altera_Forum
Honored Contributor
8 years ago
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In my opinion the compiler sees the IORD result as an integer, and will cast it to a float value. I think the only way you could get around this is by using pointers and changing the pointer type. Something like (not tested):
float x,v; *((unsigned int*)&x)= IORD(IOREG_BASE,0); // Reading from the register1 defined in H/W v= x+2; IOWR(IOREG_BASE,1,*((unsigned int*)&v)); // Writing to register2 defined in H/W

I don't know if there is a more elegant way to do it...
--- Quote End ---

Thanks a lot! This solved my problems too