user access to physical memory

user access to physical memory

[David Ho]

Hi all,

I know this question has been asked before, but I can't seem to find it in
the archive.

How do I get access to physical memory from user space?  I want to write a
simple test problem to access the frame buffer directly on the LCD
controller.

Thanks,

David Ho
Nanometrics Inc.


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Re: user access to physical memory

[Wolfgang Denk]

In message <OFD0681AD7.24E6EB05-ON85256E8B.004961BC-85256E8B.0049B26E@nanometrics.ca> you wrote:
>
> I know this question has been asked before, but I can't seem to find it in
> the archive.

You mean a simple search for "physical memory" like this one:

http://lists.linuxppc.org/results.html?restrict=linuxppc-embedded&words=physical+memory

didn't give you any results? Strange... I get quite a lot of messages.

> How do I get access to physical memory from user space?  I want to write a
> simple test problem to access the frame buffer directly on the LCD
> controller.

See the archives.

Best regards,

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
A conservative is a man with two perfectly good legs  who  has  never
learned to walk.                              - Franklin D. Roosevelt

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Re: user access to physical memory

[David Ho]

> >
> > I know this question has been asked before, but I can't seem to find it
in
> > the archive.
>
> You mean a simple search for "physical memory" like this one:
>
> http://lists.linuxppc.org/results.html?restrict=linuxppc-
> embedded&words=physical+memory
>
> didn't give you any results? Strange... I get quite a lot of messages.
>

searching for /dev/mem gave me more useful results.

David


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devfs with ramdisk problem

[dong in kang]

 I've had trouble with ramdisk with devfs.
I've used the Linux Linux v.2.4.22 for months on a custom PPC board.
I frequently changed the kernel and the content of the ramdisk.
Sometimes, booting fails with the following error messages.
--------- error messages -------
RAMDISK: Compressed image found at block 0
RAMDISK: nblocks = 0
RAMDISK: crd_load, kmalloc(4096, 496)
Freeing initrd memory: 5204k freed
VFS: Mounted root (ext2 filesystem).
Mounted devfs on /dev
VFS: Cannot open root device "rd/0" or 00:00
Please append a correct "root=" boot option
Kernel panic: VFS: Unable to mount root fs on 00:00
--------- end of error messages ---------
When it happens, sometimes I could make it work with the same kernel and
ramdisk but with different kernel configuration (esp. turning on/off
debugging flags of Kernel hacking menu).
However, now it keeps failing.

 Can anybody help me?

The RAMDISK size is 30M, the memory of the system is 128M, and the size of
zImage.initrd is about 7M. And the kernel command line is:
mem=128M load_ramdisk= 1 ramdisk_size=30720 console=ttyS0,57600
root=/dev/rd/0 init=/bin/sh


 Thanks,

 Dong-In


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