Isaac Marino Bavaresco wrote:

> Em 31/3/2011 23:36, Gerhard Fiedler escreveu:
>> Andre Abelian wrote:
>>
>>> From: Gerhard Fiedler=20
>>>
>>>> Andre Abelian wrote:=20
>>>>
>>>>> I started writing a test code for SST25VF032   32mb flash the
>>>>> problem I am facing is the counter I am using to add counts each
>>>>> time if I want to update I have to erase 4k block of memory so I
>>>>> have to waist 4k to keep counter going from 0 to 5000. Microchip
>>>>> eeproms any individual memory can be read or write. what would
>>>>> you guys do?=20
>>>> Put the counter on a different storage (e.g. an on-chip EEPROM)?=20
>>> that was my mistake I did. pic24 doesn't have internal memory and I
>>> put external eeprom first but I removed it. my next update I will
>>> put small size eeprom.
>> Well, then you have to use one page of the flash for that. There are
>> several ways to do this that don't require erasing and rewriting the
>> page all the time.=20
>>=20
>> For example, you can erase it (all bits set), then clear one bit
>> after the other as you write your record -- one bit per record. That
>> gives you in one 4k page 4k x 8 =3D 32k records. Not quite enough to
>> fill the whole 32MB flash with records. You'd need 7 pages for this.
>>=20
>>=20
>> As a variant, you can use the first byte as a "page counter". Set it
>> to 0 the first time, then increment it with each time you reach the
>> end of the index page and have to start over.=20
>>=20
>> Or you store the index number of the last record written in the
>> first page. The next time you write a record you search for the
>> first free position and store the next index number there. When you
>> reach the end of the first page, you erase it and start over at the
>> first position of the page.=20
>>=20
>> There are other variants of this type. It all depends on your
>> constraints.
>=20
> I don't know this particular device, and I think it is one of the
> smaller devices that have less complications in their operation.=20
>=20
> Beware of some FLASH memories (bigger ones), because they can only be
> erased in much larger blocks.=20
>=20
> One 2Gbit device I use for instance, it can be programmed in blocks
> of 2kbyte but can be erased only in pages of 128kbyte (64 programming
> blocks at once). Besides, it is strictly forbidden to program one
> block twice without before erasing the whole page it is located.=20
>=20
> For this type of device you will really need a suitable FLASH file
> system. We use yaffs2, but it is very memory consuming (in the range
> of Mbyte). Another option is jffs.=20

Good points. However, IIRC he said that after writing each 150 byte
block of data, the power is removed from the chip. In such a case, I
don't think that a flash file system will help much.

Gerhard
--=20
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