The history of this is that I needed a block number to signify "invalid
block". The value had to fit in with the use of 16 bits in the chunk grouping
mechanism etc. I could have used 0xFFFF/0xFFFFFFFFFF but that would have been
a bit messier in code and 0 was simpler.
Since block 0 is guaranteed to be good on NAND, it is sometimes used as a
special block to store information. Thus, I decided to use zero as "invalid
block" and "invalid chunk group".
You can potentially get around this by modifying the flash access code to map
start(-1) == physical block 0, and this **should** work - perhaps with minor
tweaks - but I have not tested this.
-- CHarles
On Thursday 17 June 2004 13:34, guxm wrote:
> Further,
> So I think such design is deliberate, strict, or to say correct. The
> dev->startBlock or endBlock is only a digital number. As for which physical
> block we map it to, we can just do it.
>
> Best regards
> GUXM
>
> Hi,
>
> I have the same question. I have tried to modify device.startBlock = 0, But
> I found that there is much code use 0 to check chunkId validation. So I
> have to map logical block n to physical block n-1. That is the
> dev->startBlock(=1) is mapped to physical block 0. It's OK now.
>
> For example:
> yaffs_PutChunkIntoFile()
> {
> existingChunk = tn->level0[chunkInInode & YAFFS_TNODES_LEVEL0_MASK];
>
> ... ...
> if(existingChunk == 0)
> {
> in->nDataChunks++;
> }
>
> }
>
> yaffs_DeleteChunk()
> {
> if( chunkId <= 0 )
> return;
> }
>
> yaffs_GetObjectName()
> {
> else if(obj->chunkId <= 0)
> {
> char locName[20];
> sprintf(locName,"%s%d",YAFFS_LOSTNFOUND_PREFIX,obj->objectId);
> strncpy(name,locName,buffSize - 1);
> }
> }
>
>
> Best regards
> guxm
>
>
> ======= 2004-06-15 21:39:00 ÄúÔÚÀ´ÐÅÖÐдµÀ£º=======
>
> >In lots of the source files, the following line of code is used
> >
> ><code>
> > device.startBlock = 1; // Don't use block 0
> ></code>
> >
> >Having searched through the docs and sources, I've found no clue why block
> >0 is different that the rest of the device blocks.
> >
> >Please, anyone, enlighten me.
> >
> >Thanks,
> >Jacob Dall
> >
> >
> >
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>
>
>
>
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