bus access for NAND parts

[Matthieu CASTET]

Ricard Wanderlof a écrit :
> On Thu, 30 Oct 2008, Cliff Brake wrote:
> 
>> Correction -- above should say:  "It seems that most devices simply use a
>> _GPIO_ for CE".  The chip select is set low in software, and then
>> multiple bus cycles are run to execute the address and data phases of
>> the NAND operation.  So what keeps another process from interrupting
>> this and running a bus cycle while the GPIO for NAND CE is still low
>> -- which would toggle the strobes to the NAND cs.
> 
> I don't know in general, but in several systems that have multiple buses, 
> the NAND flash can be the only device on a particular bus, so conflicts 
> with other devices are not an issue in those cases. Otherwise, it would be 
> as you say, I agree.
> 
The s3c2412 where the nand bus is shared with SDRAM. nCE is like a gpio
set by software. But it isn't a problem because the nand flash doesn't
care about other bus cycle if nWE/nRE is in high state (see nand
datasheets).

So the arbitration is done with nWE/nRE line and without nCE.

Matthieu