Atomic compare_and_swap function

--- Quote Start ---

originally posted by kwokwong@Nov 2 2006, 10:14 PM

hi all,

according the header file (d:\altera5\kits\nios2_50\bin\eclipse\plugins\com.microtronix.nios2linux.uclibc_1.4.0\include\bits\atomicity.h),

the implemented function is only stub (not really atomic!).

does anyone know how to do it really atomic?

i thought that the simplest way is to disable the interrupt when doing this function and re-enable the interrupt afterwards.

so i need to know how to enable/disable interrupt ??

regards,

kwok wong

<div align='right'><{post_snapback}> (index.php?act=findpost&pid=19104)

--- quote end ---

--- Quote End ---

It is not implemented, so we need a nios2 version in,

uClibc/libc/sysdeps/linux/nios2/bits/atomicity.h

Look at other arch, eg, arm,m68k,mips,i386, they use locked exchange instead of disable interrupt.

Are there locked instructions in Nios2?

--- Quote Start ---

originally posted by hippo+nov 2 2006, 11:52 pm--><div class='quotetop'>quote (hippo @ nov 2 2006, 11:52 pm)</div>

--- quote start ---

<!--quotebegin-kwokwong@Nov 2 2006, 10:14 PM

hi all,

according the header file (d:\altera5\kits\nios2_50\bin\eclipse\plugins\com.microtronix.nios2linux.uclibc_1.4.0\include\bits\atomicity.h),

the implemented function is only stub (not really atomic!).

does anyone know how to do it really atomic?

i thought that the simplest way is to disable the interrupt when doing this function and re-enable the interrupt afterwards.

so i need to know how to enable/disable interrupt ??

regards,

kwok wong

<div align='right'><{post_snapback}> (index.php?act=findpost&pid=19104)

--- quote end ---

--- Quote End ---

It is not implemented, so we need a nios2 version in,

uClibc/libc/sysdeps/linux/nios2/bits/atomicity.h

Look at other arch, eg, arm,m68k,mips,i386, they use locked exchange instead of disable interrupt.

Are there locked instructions in Nios2?

<div align='right'><{post_snapback}> (index.php?act=findpost&pid=19108)</div>

[/b]

--- Quote End ---

$ find uClibc -name "atomic*.h"

uClibc/libc/sysdeps/linux/sh/bits/atomic.h

uClibc/libc/sysdeps/linux/arm/bits/atomicity.h

uClibc/libc/sysdeps/linux/i386/bits/atomic.h

uClibc/libc/sysdeps/linux/i386/bits/atomicity.h

uClibc/libc/sysdeps/linux/m68k/bits/atomicity.h

uClibc/libc/sysdeps/linux/mips/bits/atomic.h

uClibc/libc/sysdeps/linux/mips/bits/atomicity.h

uClibc/libc/sysdeps/linux/alpha/bits/atomic.h

uClibc/libc/sysdeps/linux/alpha/bits/atomicity.h

uClibc/libc/sysdeps/linux/h8300/bits/atomicity.h

uClibc/libc/sysdeps/linux/sparc/bits/atomicity.h

uClibc/libc/sysdeps/linux/common/bits/atomic.h

uClibc/libc/sysdeps/linux/common/bits/atomicity.h

uClibc/libc/sysdeps/linux/x86_64/bits/atomic.h

uClibc/libc/sysdeps/linux/x86_64/bits/atomicity.h

uClibc/libc/sysdeps/linux/powerpc/bits/atomic.h

uClibc/libc/sysdeps/linux/powerpc/bits/atomicity.h

uClibc/include/bits/atomic.h

uClibc/include/bits/atomicity.h

uClibc/include/atomic.h

If we create uClibc/libc/sysdeps/linux/nios2/bits/atomicity.h ,then it will become uClibc/include/bits/atomicity.h . Otherwise, it will come from uClibc/libc/sysdeps/linux/common/bits/atomicity.h, which is a stub.

If nios2 does not have lock, then we can use disable/enable interrupr, with inline assembly.

Look in include/asm (ie, asm-nios2nommu) /system.h

Use,

local_irq_save(x) // to disable global irq

then,

local_irq_restore(x) // to enable/restore global irq

--- Quote Start ---

originally posted by hippo@Nov 7 2006, 12:47 AM

look in include/asm (ie, asm-nios2nommu) /system.h

use,

local_irq_save(x) // to disable global irq

then,

local_irq_restore(x) // to enable/restore global irq

<div align='right'><{post_snapback}> (index.php?act=findpost&pid=19239)

--- quote end ---

--- Quote End ---

Thank you, hippo!

F.Y.I.

Use the macro COMPARE_AND_SWAP in stead of the function compare_and_swap.

E.g.

static inline int __compare_and_swap(volatile int *p, int old_val, int new_val)

{

int result;

unsigned long int_context;

/* save int. and disable all interrupts */

local_irq_save(int_context);

result = compare_and_swap((volatile long*)p, old_val, new_val);

/* re-enable interrupt */

local_irq_restore(int_context);

return result;

}

# define COMPARE_AND_SWAP(addr, old_val, new_val)

__compare_and_swap(addr, old_val, new_val) http://forum.niosforum.com/work2/style_emoticons/<#EMO_DIR#>/smile.gif