Thread (44 messages) 44 messages, 12 authors, 2009-11-01

RE: Accessing flash directly from User Space

From: Jonathan Haws <hidden>
Date: 2009-10-28 14:39:03

On Tue, Oct 27, 2009 at 04:24:53PM -0600, Jonathan Haws wrote:
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How can I get that pointer?  Unfortunately I cannot simply
use
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the
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address of the flash.  Is there some magical function call
that
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gives me access to that portion of the memory space?

$ man 2 mmap

You want MAP_SHARED and O_SYNC.

To use that I need to have a file descriptor to a device, do I
not?  However, I do not have a base flash driver to give me that
file descriptor.  Am I missing something with that call?
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/dev/mem
Okay, I now have access to the flash memory, however when I write
to it the writes do not take.  I have tried calling msync() on the
mapping to no avail.  I have opened the fd with O_SYNC, but cannot
get things to work right.
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Here are the calls:

int fd =3D open("/dev/mem", O_SYNC | O_RDWR);
uint16_t * flash =3D (uint16_t *)mmap(NULL, NOR_FLASH_SIZE,
		(PROT_READ | PROT_WRITE), MAP_PRIVATE, fd,
		NOR_FLASH_BASE_ADRS);
=20
What board and CPU are you using?  Is your flash really at
0xFC800000, or is
that the virtual address that VxWorks puts it at?
I am using a custom board based on the AMCC Kilauea development board.  It =
uses a 405EX CPU.  Yes, the flash is really at 0xFC000000.
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