Question regarding NIOS II custom registers

Altera_Forum · ‎04-01-2005

I read the Nios2 custom instruction reference book online, and found that the only way I could read or write data from custom registers is to change the assembly code (change rA or rB to cA and cB).

However, if I were to load the C program directly to the Nios board, the IDE will never know that I use custom registers. (because when it compiles, IDE automatically assign all the variables to Nios registers)

so my question is how do I let the IDE compiler know that some of my custom instructions use custom registers instead of Nios registers?

any suggestions will be very appreciated http://forum.niosforum.com/work2/style_emoticons/<#EMO_DIR#>/smile.gif

Altera_Forum · ‎04-01-2005

I'm not sure exactly what you mean here.

What assembly code do you want to generate? And what's being generated?

The best way to get custom instructions emitted is to use a function from the __builtin_custom family, or the wrapper which is built around it within system.h.

If this isn't flexible enough then you can also use asm() statements within C code but you must make sure you get your constraints right as otherwise the generated code will be very inefficient or wrong.

Altera_Forum · ‎04-02-2005

okei let me rephrase my question in a simpler way:

after I use the __builtin_custom functions, how do I let the compiler know that I am using custom registers instead of NIOS2 registers?

__builtin_custom only tells the compiler that I am using custom instructions, but it does not give informations to custom REGISTERS~

Altera_Forum · ‎04-02-2005

The compiler won't be able to use your custom registers. You'll have to manage them yourself explicitly.

Altera_Forum · ‎04-03-2005

Thanks James & wombat~

I guess I'll use asm() to do it...