mmap : please help !

mmap : please help !

[scarayol]

Hi all,

I need somme help : I wrote driver like /dev/mem to read and write into=

physical memory at specific addresses. For that, I use instruction mmap=

like that :


    if((mem_mc_fd =3D open("/dev/map_mc",O_RDWR | O_SYNC)) < 0)
    {
        printf("\nProbleme pour ouvrir /dev/map_mc\n");
        exit(-1);
    }

 // mapping de la zone correspondante
    pmapMC =3D (DisqueMC *)mmap (0,MC_SIZE, PROT_READ | PROT_WRITE |
PROT_EXEC, MAP_SHARED, mem_mc_fd, MC_BASE_ADDRESS);
    if (pmapMC =3D=3D MAP_FAILED)
    {
        printf("Erreur de mmap pour MC:%d,%s\n",errno, strerror(errno))=
;
         close(mem_mc_fd);
 }

I use function pread, pwrite to access datas within the driver function=
s
but, I should prefer to use pmapMC pointer (by the mean of this virtual=

address) that points to a structure. I thought that it was the same to
access to the physical memory to use the pointer or to use read, write =
on
the file (by mem_mc_fd), but it seems to have different results. What i=
s
wrong ? What is the good manner to read or write in the physical memory=
?

Thanks a lot.

----------------------------------------------------------
Sophie CARAYOL

TECHNOLOGIES & SYSTEMES
50 rue du Pr=E9sident Sadate
F - 29337 QUIMPER CEDEX

T=E9l: +33 2 98 10 30 06
mailto:scarayol@assystembrime.com
----------------------------------------------------------
=

mmap : please help !

[scarayol]

Hi all,

I need somme help : I wrote driver like /dev/mem to read and write into=

physical memory at specific addresses. For that, I use instruction mmap=

like that :


    if((mem_mc_fd =3D open("/dev/map_mc",O_RDWR | O_SYNC)) < 0)
    {
        printf("\nProbleme pour ouvrir /dev/map_mc\n");
        exit(-1);
    }

 // mapping de la zone correspondante
    pmapMC =3D (DisqueMC *)mmap (0,MC_SIZE, PROT_READ | PROT_WRITE |
PROT_EXEC, MAP_SHARED, mem_mc_fd, MC_BASE_ADDRESS);
    if (pmapMC =3D=3D MAP_FAILED)
    {
        printf("Erreur de mmap pour MC:%d,%s\n",errno, strerror(errno))=
;
         close(mem_mc_fd);
 }

I use function pread, pwrite to access datas within the driver function=
s
but, I should prefer to use pmapMC pointer (by the mean of this virtual=

address) that points to a structure. I thought that it was the same to
access to the physical memory to use the pointer or to use read, write =
on
the file (by mem_mc_fd), but it seems to have different results. What i=
s
wrong ? What is the good manner to read or write in the physical memory=
?

Thanks a lot.

----------------------------------------------------------
Sophie CARAYOL

TECHNOLOGIES & SYSTEMES
50 rue du Pr=E9sident Sadate
F - 29337 QUIMPER CEDEX

T=E9l: +33 2 98 10 30 06
mailto:scarayol@assystembrime.com
----------------------------------------------------------

=

RE: mmap : please help !

[Fillod Stephane]

Sophie CARAYOL wrote:
[...]
> What is the good manner to read or write in the physical memory?

Please have a look at Denx's FAQ for accessing memory bus:

=20
http://www.denx.de/twiki/bin/view/PPCEmbedded/DeviceDrivers#Section_Acce
ssingPeripheralsFromUserSpace
or shorter: http://tinyurl.com/6c7th

Depending on the O_SYNC flag passed to open, the mmap'ed memory will be
accessed through non guarded cache or not. See linux/drivers/char/mem.c.
The ppc instruction "eieio" deals with I/O ordering.


Kenavo
--=20
Stephane

PS: be careful not sending twice the same mail to the list=20