[ts-7000] Using NVRAM on TS7250

["naturalwatt" <>]

Hi.  Some time ago I asked if there was a way of writing to Flash when a system 
was being 
powered down.  The replies convinced me to not even thinking about this as it 
was likely 
to lead to filesystem corruption.  Someone suggested usng the TS- NVRAM board, 
but I 
only needed to store a single timestamp of 8 bytes.

In discussion with Eddie, it looks like the right thing to do is use the 114 
NVRAM bytes 
available in the RTC - assuming you have one.  It so happens I do.

In order to access the NVRAM, you need the NVRAM driver. You can either compile 
the full 
kernel with the CONFIG_NVRAM=y or create a loadable module.  To do this, 

make ts7520_config
make old_config

to get the basic config there.  Then edit .config (carefully reading all the 
instructions 
telling you not to do this) and change
# CONFIG_NVRAM not set
to
CONFIG_NVRAM=m

note the m, for module.

Then run "make modules".  You certainly don't need to build the whole kernel.  
Unless you 
want to.

This will have created drivers/char/nvram.o. Copy this to the 7250 into
/lib/modules/2.4.26-ts11/kernel/drivers/char/nvram.o
It's md5sum is 031a3c521b089919e5fd7ded72e8f7a1 and size is 9488.

I am more than happy to post this somewhere if there is a good place to do so.

To load it, simply run insmod nvram.  You will have to do something to make 
sure this 
module is loaded at evey power up; I put a script and link in /etc/init.d

This will create /dev/misc/nvram, a character file you can read and write. 
Except that you 
can't until the checksum is initialised!  Until you do this, any access will 
give error 5, 
Input/Out Error.

In order to initialise the checksum you need to use a special IOCTL on this 
device. It only 
ever has to be done once, as the entire point of this RAM is that it is 
non-volatile.

Here is a small program to do this.  I can also post the source and a compiled 
version, if 
people are interested.

nvraminit.c

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <linux/nvram.h>

int main (int argc, const char * argv[]) {
        int fd;
        if (fd = open("/dev/misc/nvram", O_RDWR) < 0) {
                fprintf(stderr, "Open of /dev/misc/nvram failed %d %s\n", 
errno, strerror(errno));
                exit(errno);
        }
        
        if (ioctl(fd, NVRAM_INIT, 0) < 0) {
                fprintf(stderr, "Init ioctl failed %d %s\n", errno, 
strerror(errno));
                exit(errno);
        }
        close(fd);
    return 0;
}

Hope this helps.  I expect a similar approach will work on any TS system, not 
just a TS250.

Martin







 
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