[ltp] Storing data in /dev/nvram

[Onno Benschop]

Watching this list with protracted discussions about how batteries work=20
and how bits and pieces hang together at a low level, I thought I'd jump =

in with a low-level question of my own.

I have a need to store two bytes of data between reboots. The machine is =

built into a car and the hard-disk is read-only. I don't want to=20
particularly setup my machine to write to the hard-disk, and if I could=20
make that the head never writes, I would.

I hit on the idea of storing data in CMOS somewhere, don't really care=20
where, as long as I can store two bytes every five minutes or so, and=20
read them when the machine boots.

I investigated using libsmbios, even downloaded and compiled it, but=20
then found that it needs a later kernel, and all manner of other stuff=20
would need to happen - way too complicated.

I then thought of storing the two bytes in the RTC, but my chosen=20
location - epoch - only works on Alpha's, and I'm using an x86 board.

So, then someone suggested I investigate /dev/nvram.

I did.

I can read from it, store the data into a file, presumably modify the=20
read file, then write it back.

What I don't know is what else is stored there, which bytes I can play=20
with - I come from a 6502 world where you can PEEK and POKE, but that's=20
a story for a different email :-)

So, who can tell me what I can read to get some answers, or can I just=20
store what ever I want in those 114 bytes?

If it matters, the board is an Intel D810EMO.

If my suggestion for writing into /dev/nvram doesn't work, what about=20
modifying the boot logo?



Cheers in anticipation,

--=20
Onno Benschop

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