Accessing flash directly from User Space [SOLVED]

[Jonathan Haws]

> > On Tue, Oct 27, 2009 at 04:24:53PM -0600, Jonathan Haws wrote:
> > >> >>> How can I get that pointer?  Unfortunately I cannot simply
> > use
> > >> the
> > >> >>>
> > >> >> address of the flash.  Is there some magical function call
> > that
> > >> >> 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?
> > >> >
> > >>
> > >> /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.
> > >
> > >Here are the calls:
> > >
> > >	int fd = open("/dev/mem", O_SYNC | O_RDWR);
> > >	uint16_t * flash = (uint16_t *)mmap(NULL, NOR_FLASH_SIZE,
> > >			(PROT_READ | PROT_WRITE), MAP_PRIVATE, fd,
> > >			NOR_FLASH_BASE_ADRS);
> >
> > 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.

I have found the problem.  It occurred to me in the shower (okay not really, but most good ideas happen there).

What was happening is that I was in fact able to write to the correct registers.  However, I would try and write to them in a batch.  But the way mmap works (at least according to the man page) with MAP_SHARED is that the file may not be updated until msync() is called.  Now, I thought that O_SYNC would take care of that when I open /dev/mem, but that was not the case.

Anyway, to make a long story short, I inserted an msync() after each assignment to the flash.  This resolved my problem and I can now program my flash.

Thanks everyone for your help!

Jonathan