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

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Hi Bo,

On Wed, 17 Jul 2013 18:27:29 +0800, Bo Shen <voice.shen@atmel.com>
wrote:

> Hi Albert,
> 
> On 07/17/2013 06:10 PM, Albert ARIBAUD wrote:
> > Hi Bo,
> >
> > On Wed, 17 Jul 2013 17:14:17 +0800, Bo Shen <voice.shen@atmel.com>
> > wrote:
> >
> >> As both the DDR SDRAM and NAND flash connect to EBI on at91sam9n12
> >> and share the lower 8 bits data line. If use low drive of the data
> >> line, it will cause DDR data access corrupt in lower address, so
> >> change the data line to high drive mode
> >>
> >> This will fix the Linux kernel boot issue when use Lower address
> >
> > Wait--does this mean that there is no separate chip selects for NAND and
> > DDR on this SoC?
> 
> No. The NAND and DDR has there own chip selects.
> This is chip specific. If DDR and NAND share data line, if we use low 
> drive for EBI IO, it will cause DDR low memory address content corrupt. 
> For example, if the DDR base address is 0x20000000, if we use 0x20008000 
> as entry address of Linux kernel, then it won't boot up successfully. 
> So, if we need to use low memory address, we need this to fix.

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.

> Best Regards,
> Bo Shen

Amicalement,
-- 
Albert.