[U-Boot-Users] flash question

[Wolfgang Denk]

In message <200412041407.32014.mail at stefan-roese.de> Stefan Roese wrote:
> 
> On Saturday 04 December 2004 13:51, jack W wrote:
> >     i am a newer  i have a question about flash  , i have a nor flash and
> > its type is SST39VF160 . I don't know how to set the CFG_MAX_FLASH_SECT.

Jack: there is a standard way of finding out thing one doesn't  know:
RTFM!!!

In this case the Manual is the SST39VF160 datasheet, which can easily
be found (first hit when googeling for "SST39VF160"). It's at
http://www.sst.com/downloads/datasheet/S71145.pdf

> > the flash's sector is 2k .and i think that the CFG_MAX_FLASH_SECT is
> > 4096/2=2148  right?

No. This flash can be operated in sector mode, with a uniform  sector
size  of  2 KWords, or in block mode, with a uniform block size of 32
KWords. The datasheet uses "x16" or 16 bit "words". So one sector  is
4  KiB  (Kibibyte - to use the official SI unit), and the size of one
block is 64 KiB. Given a total size of 2 MiB or 2048 KiB,  there  are
512 sectors or 32 blocks on the chip.

So any number between 32 and 512 may be correct for your system...

Depending on how you want to use your flash  device  you  can  either
decide  to  use sectors (fine grid; advantage: low cut, disadvantage:
many sectors to erase, thus long erase  times),  or  blocks,  or  any
combination of it.

I'd recommend to use blocks normally, but secors for one block (using
one or more sectors to store the  U-Boot  envrionment).  For  such  a
configuration, CFG_MAX_FLASH_SECT = 47 would be correct.

> No! You have to configure the maxmium sector count with this define (and _not_ 
> the sector-size!). Most of the time I set this to 256. This should sufficient 
> for most flash's.

Stefan: as you can see, this is actually a bad advice, as it would be
wrong here.

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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