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Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
14 years ago

Linux with MMU acessing registers

Hello i need to acess my registers from userspace, i am developing a

critical timing application and i can't consider the time needed to

call the device driver and read my timestamp register.

I need to read my timestamp register from userspace, how can i do

that? I know that 0x8 is for uncached, therefore peripherals adresses

will have the 8 in the adress.

I am trying to use inl(0x000024e0 (my adress), 0);

however i get a segmentation fault... i tried to include io.h but with no sucess

# define inl(addr)

({

unsigned int __res;

__asm__ __volatile__(

"ldwio %0, 0(%1)"

: "=r"(__res)

: "r" (addr));

__res;

})

//-----------------------------------------------------------------------

# define inb(addr)

({

unsigned int __res;

__asm__ __volatile__(

"ldbio %0, 0(%1)"

: "=r"(__res)

: "r" (addr));

__res;

})

//-----------------------------------------------------------------------

# define outl(b,addr)

({

__asm__ __volatile__(

"stwio %0, 0(%1)"

: : "r"(, "r" (addr));

})

//-----------------------------------------------------------------------

# define outw(b,addr)

({

__asm__ __volatile__(

"sthio %0, 0(%1)"

: : "r"(, "r" (addr));

})

//-----------------------------------------------------------------------

# define outb(b,addr)

({

__asm__ __volatile__(

"stbio %0, 0(%1)"

: : "r"(, "r" (addr));

})

4 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    Please don't cross-post between the mailing list and the nios2-dev list. Or if you do so, please at least link put a link to the other, so people searching for answers to the same or similar questions can find it in the other place too.

    As already stated on nios2-dev, this won't work (for obvious reasons). Please see http://article.gmane.org/gmane.linux.uclinux.nios2.devel/189 for the full answer.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    This is my final code

    memfd = open("/dev/mem", O_RDWR | O_SYNC );

    if (memfd < 0)

    {

    log_msg("Cannot open /dev/mem\n");

    exit(1);

    }

    pgoff = (unsigned int) (MENOS_BASE & (sysconf(_SC_PAGE_SIZE)-1));

    map_len = 16 + pgoff;

    mapped = mmap(NULL, map_len, (PROT_READ | PROT_WRITE),

    MAP_SHARED, memfd, MENOS_BASE - pgoff);

    if (mapped == MAP_FAILED )

    {

    log_msg("Cannot map registers\n");

    }

    ts_my = mapped + pgoff;

    inl(ts_my);