Hi Nick, without looking into the details of this patch: According to your description, I see two possible issues, depending on the real flash device used:
1.) Some devices data sheets explicitly allow only ONE program cycle per byte/word after an erase cycle. Background: - Even when programming a '1' into a cell, some charge may trickle and if that happens multiple times, a '1' may come closer to the '1'->'0' boundary. Charge leakage over the years may then loose the intended content of the cell much earlier than the data rentention time mentioned in the data sheet specifies. -> You may see data loss already after e.g. 2 years, and not only after 10 years. - When a '0' is programmed into a cell multiple times without erasing it first, it may get overcharged and therefore hold a voltage outside the intended voltage band. This may overstress the device, reducing the lifetime of the device. 2.) Some devices store a hidden ECC signature together with the user data. For these devices, a flash line (e.g. 64 bit) can only be programmed once without an intermediate erase, because even if only some user data bits flips from 1 to 0, the new data pattern may end in a ECC signature that switches some bits from 0 to 1. ----- Since your patch is shared code, it should only be applied if you made sure that its behaviour is allowed for ALL devices that are handled with this code. wkr, Thomas. Am 17.01.2014 02:50, schrieb Nick Withers: > Hi all, > > The attached patch makes a (n admittedly not very pretty, but minimal) > change to powerpc/shared/flash/flash.c so that it won't try to erase a > flash segment just because the existing contents aren't all-1s. Now, so > long as no bits would have to be changed from a 0 to a 1 an erase is not > necessarily required. > > With this change I've been able to use the spansionFlash driver to bring > up a JFFS2 file-system, reading and writing files, which failed without. > > > > _______________________________________________ > rtems-devel mailing list > rtems-devel@rtems.org > http://www.rtems.org/mailman/listinfo/rtems-devel > -- -------------------------------------------- embedded brains GmbH Thomas Doerfler Dornierstr. 4 D-82178 Puchheim Germany email: thomas.doerf...@embedded-brains.de Phone: +49-89-18 94 741-12 Fax: +49-89-18 94 741-09 PGP: Public key available on request. Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG. _______________________________________________ rtems-devel mailing list rtems-devel@rtems.org http://www.rtems.org/mailman/listinfo/rtems-devel
