How do I access nvRAM from user space?

How do I access nvRAM from user space?

[Bruce_Leonard]

Sorry for the dumb question, I just can figure out the right google search 
to find what I'm trying to do.  I'm running 2.6.27-rc4 on an mpc8347 with 
a 32KiB nvSRAM (Cypress CY14B256L) on the local bus.  We just want to be 
able to access this memory from user space seperately from "main" memory. 
We've got a process that needs to be able to remember info through power 
cycles.  Can anyone point me to an article or some code snippet that does 
something like this so I can sink my teeth into it?

Bruce

Re: How do I access nvRAM from user space?

[yanjun.luo]

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Hi Bruce,
You can use mmap to access NVRAM from user space, but you should config 
local bus first, like width, speed etc.

Regards,
Yanjun Luo.




发件人： Bruce_Leonard@selinc.com 
发送时间： 2008-09-25  11:44:56 
收件人： linuxppc-embedded@ozlabs.org 
抄送： 
主题： How do I access nvRAM from user space? 
 
Sorry for the dumb question, I just can figure out the right google search 
to find what I'm trying to do.  I'm running 2.6.27-rc4 on an mpc8347 with 
a 32KiB nvSRAM (Cypress CY14B256L) on the local bus.  We just want to be 
able to access this memory from user space seperately from "main" memory. 
We've got a process that needs to be able to remember info through power 
cycles.  Can anyone point me to an article or some code snippet that does 
something like this so I can sink my teeth into it?
Bruce
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Re: How do I access nvRAM from user space?

[David Hawkins]

Hi Bruce,

> Sorry for the dumb question, I just can figure out the right google search 
> to find what I'm trying to do.  I'm running 2.6.27-rc4 on an mpc8347 with 
> a 32KiB nvSRAM (Cypress CY14B256L) on the local bus.  We just want to be 
> able to access this memory from user space seperately from "main" memory. 
> We've got a process that needs to be able to remember info through power 
> cycles.  Can anyone point me to an article or some code snippet that does 
> 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.

Cheers,
Dave

Re: How do I access nvRAM from user space?

[Bruce_Leonard]

Dave,

> > Sorry for the dumb question, I just can figure out the right google 
search 
> > to find what I'm trying to do.  I'm running 2.6.27-rc4 on an mpc8347 
with 
> > a 32KiB nvSRAM (Cypress CY14B256L) on the local bus.  We just want to 
be 
> > able to access this memory from user space seperately from "main" 
memory. 
> > We've got a process that needs to be able to remember info through 
power 
> > cycles.  Can anyone point me to an article or some code snippet that 
does 
> > 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

Bruce

Re: How do I access nvRAM from user space?

[Bruce_Leonard]

> 
> 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
> 

Never mind.  I figured out how to use mmap.  It's all in the parameter 
'off' not 'addr' :).  Thanks to everyone who responded with help.

Bruce

Re: How do I access nvRAM from user space?

[David Hawkins]

Hi Bruce,

> 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

Its pretty much:

	/* Open /dev/mem and map it */
	printf(" * open /dev/mem\n");
	fd = open("/dev/mem", O_RDWR | O_SYNC);
	if (fd < 0) {
		printf("Open /dev/mem failed - %s\n",
			strerror(errno));
		return -1;
	}
	printf(" * map %d page(s) (%d-bytes) at address 0x%.8X\n",
			mem_pages, mem_size, mem_phys);
	mem_addr = (char *)mmap(
		0,
		mem_size,
		PROT_READ|PROT_WRITE,
		MAP_SHARED,
		fd,
		mem_phys);
	if (mem_addr == (char *)MAP_FAILED) {
		printf("Error: mmap failed\n");
		close(fd);
		return -1;
	}

I'll send you the code I ripped that from, and another
example from the Busybox code.

Cheers,
Dave