[U-Boot] [PATCH] arm: at91sam9n12: change EBI IO to high drive mode

[Michael Cashwell]

On Jul 17, 2013, at 6:42 AM, Albert ARIBAUD <albert.u.boot at aribaud.net> wrote:

> I understand the symptom. What I don't undestand is how come NAND
> does not keep its data lines in high impedance when its chip select is
> inactive, which it is when DDR is being accessed.

Chip selects prevent contention but they do not make the load vanish.
A deselected chip is not electrically the same as a non-populated chip,
especially at high frequencies.

Think of it another way. CMOS pins that are input-only are always high-z
but they still must be counted as a load when adding up the fan out seen
by the upstream output driver.

-Mike