Re: [oc] EEPROM Programmers using FPGAs? now its EPROM vsFLASH ti me

[Daniel Haensse <daniel.haensse@alumni.ethz.ch>]

Chen,

David Woodhouse who is the GURU of linux jffs told me that it is not really a 
concern. The flash will survive a couple of year, even in a application where 
every couple of seconds some data is written. The file system is smart 
because it fills up the flash before it issues a flash erase. You don't need 
an additional SRAM. But of course it should be possible to use mainmemory 
SDRAM for write cache under uclinux. Anyway, the idea of jffs is that a 
sudden power failure will save the data, introducing a write cache will make 
those changes to be lost. So an SRAM with battery backup may be usefull, if 
the data are so precious, but the costs (see high end scsi controllers)...

Dani

Am Mittwoch, 9. Januar 2002 02.02 schrieben Sie:
> hi,Dani:
>
> you are right. In order to preventing frequent erasing the FLASH block or
> total FLASH chip we can
> use SRAM as write-cache which will effectivelly extend the lifetime of
> FLASH.
> However, the access times limitation must be remembered.
>
> chen.
>
> ===
>
> Am Dienstag, 8. Januar 2002 13.25 schrieben Sie:
> > It's very easy to use FLASH.
> > Martin has explained the speed of FLASH,but the one thing should be
> > carefully treated using FLASH, which is
> > it's life time.As you know FLASH has write access times limitation, when
> > a position in FLASH have been rewriten
> > up to 100,000 times it will be crashed that means you will lost your data
> > which stored in this position.So you need
> > schedule the writing access very soomthly to extend the total FLASH RAM
> > lifetime.
>
> ;-) Well if Paul would erase his eprom for 20 minutes each time. We has 4
> years of work ;-)
> There are also other types that last longer, but your right, we want to use
> jffs and we write tiny logs all the time. With such a setting the number of
> erase cycles of the chip is limited to 100'000 times. It is not that you
> can
>
> only write 100'000 times at the chip. You can write 1's down to 0's and if
> you filled up the chip, then you have to erase it again. That number of
> cycles is limited to 100'000.
>
> Dani
>
> > sincerely
> > chen
> >
> > Hi Paul,
> > <snip>
> >
> > >How easy is it to use FLASH? As easy as SRAM? What sort of access speeds
> > >do you get from them? And how much do typical units cost?
> >
> > It's as easy to read as SRAM, 80-120ns access times are typical.  Writing
> > is accomplished by sending (writing) a series of commands and data to the
> > device, for erasing pages of memory and then writing the data values and
> > write protecting and so-on.  AMD have good datasheets on their devices.
> > Dunno about prices, I tend to scrounge samples most of the time at the
> > moment :-)
> >
> > Cheers,
> > Martin
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