How do I access nvRAM from user space?

Bruce_Leonard at Bruce_Leonard at
Fri Sep 26 03:18:48 EST 2008


> > Sorry for the dumb question, I just can figure out the right google 
> > to find what I'm trying to do.  I'm running 2.6.27-rc4 on an mpc8347 
> > a 32KiB nvSRAM (Cypress CY14B256L) on the local bus.  We just want to 
> > able to access this memory from user space seperately from "main" 
> > We've got a process that needs to be able to remember info through 
> > cycles.  Can anyone point me to an article or some code snippet that 
> > something like this so I can sink my teeth into it?
> Assuming your bootloader sets up the local bus access windows
> (physical address of the SRAM) and timing so that you can
> read/write to the SRAM, then once Linux boots, you should be
> able to just use /dev/mem as you would to access any other
> device registers at a specific address.

Thanks for the reply.  So if my nvSRAM device is located at 0xb0000000 in 
physical memory, what would the mmap() call look like?  Also, do I need to 
have a device tree entry for the kernel to know about the memory?  I can 
access the device in uboot so I know it works, but I can't figure out the 
mmap to get it from linux


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