Non-volatile counter implementation

On Thu, 17 Aug 2006 20:20:42 GMT, "andrew queisser"
<andrewdotqueisser@hp.com> wrote:

>Hi all,
>
>I'm thinking of ways to implement a nearly non-volatile counter using flash 
>and RAM. Idea is to count events in a RAM counter and write the count to 
>flash every n times. At first I thought I'd just use successive locations in 
>flash until I need to reformat the entire sector but I'm thinking it may be 
>better to flip single bits from 1 to 0 with each bit indicating n events. 
>That way I don't waste an entire DWORD for each update.

If count only [m/n] , can you live with the fault between successive
runs ?

E.g. a zero-bit means 8 runs, so
0xfe => 1..8 runs
0xfc => 8..16 etc.

But the main problem stays, you have to erase the flash at a time in
the future.

But why not realy storing the 32bit value (btw. DWORD on an ARM CPU
would mean 64bit :-)

Assume an (flash) array of 128 elements, all initialized to 0xff,
if an element is 0 => take next
if an element is > 0 && < 0xffffffff => last count stored
if an element is 0xffffffff => free
(Note: count of 0xffffffff cannot be stored, special handling
is needed.)

If you no free element, erase all and start with first.

After storing a new count, clear all bits of the last.

Sound fairly easy to implement.

-- 
42Bastian
Do not email to bastian42@yahoo.com, it's a spam-only account :-)
Use <same-name>@monlynx.de instead !

On 17-Aug-2006, "andrew queisser" <andrewdotqueisser@hp.com> wrote:

> I'm thinking of ways to implement a nearly non-volatile counter using
> flash
> and RAM. Idea is to count events in a RAM counter and write the count to
> flash every n times. At first I thought I'd just use successive locations
> in
> flash until I need to reformat the entire sector but I'm thinking it may
> be
> better to flip single bits from 1 to 0 with each bit indicating n events.
> That way I don't waste an entire DWORD for each update.
>
> Does anybody know of a ready-made solution for this kind of thing?
>
> Thanks,
> Andrew

I use a "power going down" interrupt, and save off counters (and other
things)
as the power is going down.

-Hershel

"42Bastian Schick" <bastian42@yahoo.com> wrote in message 
news:44e5aaf9.367450565@news.individual.de...
>
> If count only [m/n] , can you live with the fault between successive
> runs ?
>
> E.g. a zero-bit means 8 runs, so
> 0xfe => 1..8 runs
> 0xfc => 8..16 etc.
>
> But the main problem stays, you have to erase the flash at a time in
> the future.
>
> But why not realy storing the 32bit value (btw. DWORD on an ARM CPU
> would mean 64bit :-)
>
> Assume an (flash) array of 128 elements, all initialized to 0xff,
> if an element is 0 => take next
> if an element is > 0 && < 0xffffffff => last count stored
> if an element is 0xffffffff => free
> (Note: count of 0xffffffff cannot be stored, special handling
> is needed.)
>
> If you no free element, erase all and start with first.
>
> After storing a new count, clear all bits of the last.
>
> Sound fairly easy to implement.

That's exactly what I had in mind. I would flip a bit every 10 cycles. If 
the power goes down between cycles I lose 10 events. My flash is good for 
about 1 million erase cycles so I really don't need to worry about erase 
cycles as much as the time hit to erase a sector. The events happen about 
every second so I could really afford to flip a bit after every single cycle 
but then I might have to worry about having to erase the sector while I'm 
doing a time-critical operation instead of waiting for the next power cycle 
which would happen when the battery gets disconnected for recharge.

Andrew

"Hershel Roberson" <hrjunk01@moment.net> wrote in message 
news:ec4fbt01hk9@enews1.newsguy.com...
>
> On 17-Aug-2006, "andrew queisser" <andrewdotqueisser@hp.com> wrote:
>
>> I'm thinking of ways to implement a nearly non-volatile counter using
>> flash
>> and RAM. Idea is to count events in a RAM counter and write the count to
>> flash every n times. At first I thought I'd just use successive locations
>> in
>> flash until I need to reformat the entire sector but I'm thinking it may
>> be
>> better to flip single bits from 1 to 0 with each bit indicating n events.
>> That way I don't waste an entire DWORD for each update.
>>
>> Does anybody know of a ready-made solution for this kind of thing?
>>
>> Thanks,
>> Andrew
>
> I use a "power going down" interrupt, and save off counters (and other
> things)
> as the power is going down.
>
> -Hershel

Hmm, I don't have one of those but maybe we should add something like that.

Thanks,
Andrew 

On Fri, 18 Aug 2006 14:20:00 GMT, "andrew queisser"
<andrewdotqueisser@hp.com> wrote:

>but then I might have to worry about having to erase the sector while I'm 
>doing a time-critical operation instead of waiting for the next power cycle 
>which would happen when the battery gets disconnected for recharge.


I think to be (power)fail-safe you'll need 3 sectors, two management
sectors and one data sector.

Only one data sector, as you are only flipping bits, you might store
the actual count in a management sector while erasing.

Two management sectors, since you sometimes have to erase one.
-- 
42Bastian
Do not email to bastian42@yahoo.com, it's a spam-only account :-)
Use <same-name>@monlynx.de instead !