CFI problems with 32bit bus and 4 devices

Nicolas Pitre nico at
Wed Jan 10 19:21:31 EST 2001

On Wed, 10 Jan 2001, David Woodhouse wrote:

> On Wed, 10 Jan 2001, Nicolas Pitre wrote:
> > No.  Usually the actual x16 flash devices are able to operate in 8-bit mode
> > (selected with a pin tied to VCC or GND I think).  Then you route four of
> > them in parallel on a 32-bit bus.
> OK, sorry - I misunderstood. I was thinking of four x16 devices in x16
> mode.  (Which would make a certain amount of sense - although you can't
> drive them all with a single bus access, you can still have all four
> writing simultaneously, hence achieving four times the write bandwidth of
> a single chip.)

This would become ugly IMHO to interleave multiple chips over multiple bus
access.  Rather make one bank follow the other instead.

> So in this case, you've essentially got 4 8-bit devices with the address
> lines all shifted left by one bit, right?
> I thought the whole point in the 8-bit emulation mode was that you just
> didn't connect the chips' A0 line, and then you pretended they really were
> 8-bit chips, rather than having to add all this extra support to the
> drivers

>From what I understand that's mostly that, except for the query structure
which gets expanded on twice the address range.  All the rest should be the


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