some questions about registers in nios2

Hi wkongwkong,

Please see the "Nios II Processor Reference Handbook":

http://www.altera.com/literature/lit-nio2.jsp (http://www.altera.com/literature/lit-nio2.jsp)

Regards,

--Scott

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originally posted by wkongwkong@Jun 22 2006, 11:15 PM

i have some questions about registers in nios2

1: the gp(r26)' function like pc as in x86 architecture ?

2: (r15-r8) is named caller-saved registers ,their function ?

3:(r16_r23),their function ?

4: when call a function, the rule of saving registers is what? between r2 to

r25 ,which should be saved ?

5: when an interrupt happen or call function , the differences between the saving registers and restore register action.

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1. I&#39;m rusty on my x86 so I&#39;m not sure of the answer to this.

2. Caller saved registers have to be saved by the calling function. So if you&#39;re writing in assembler you don&#39;t have to bother saving them.

3. They&#39;re just registers that you can do with what you will

4. When calling a function if doing it from assembler you should save the caller saved registers. If you do the call from C the compiler looks after this for you.

5. If you want to know which registers are saved for an IRQ look in the file alt_exception_entry.S in the nios2 component