imx6 NAND chip selects
hugo at hugovil.com
Mon May 12 13:32:36 PDT 2014
On 05/08/2014 11:37 AM, Huang Shijie wrote:
> On Wed, May 07, 2014 at 12:31:42PM -0400, Hugo Villeneuve wrote:
>> I am trying to connect a NAND flash device (Micron MT29F8G08) to a
>> Wandboard Dual.
>> Here is the pin mapping:
>> i.MX6 NAND flash
>> NANDF_CS0 --> CE#
>> NANDF_RB0 --> R/B#
>> NANDF_WP_B --> WP#
>> NANDF_CLE --> CLE
>> NANDF_ALE --> ALE
>> NANDF_WE --> WE#
>> NANDF_RE --> RE#
>> NANDF_D[0-7] --> I/O[0-7]
>> This NAND flash has a single chip-select.
>> I'm testing it using Linux kernel 3.15.0-rc3.
>> In the wandboard device tree file, I have added all the above gpmi
>> pins as GPMI pins.
>> I am still booting from the SD card, so at this point I am only
>> trying to detect the NAND device. Unfortunately, when the kernel
>> boots, the GPMI driver fails to register (error -19).
>> If I monitor the NANDF_CS0 line, I can see that it is pulsed low,
>> but I am not seing any activity on the NANDF_WE line.
>> However, If I monitor the NANDF_CS1 line, I can see that it is
>> pulsed low, and during the time it is low the NANDF_WE line is also
>> going low.
>> I then made sure to reconfigure the unused pins NANDF_CS[1-3] as
>> GPIOs (ALT5 function) in my device tree file. I have confirmed with
>> kernel debug traces that the iomux register for NANDF_CS1 have the
>> value 0x05, which means ALT5 function (GPIO). But I am still seeing
>> the same behavior as before on the oscilloscope.
>> So how can I configure the GPMI driver to only use NANDF_CS0 and not
>> And is it normal that NANDF_CS1 is still used by the GPMI driver
>> when configured as GPIO?
> It is not normal at all.
> Please disable the GPIO pinctrl, and only enable the pinctrl for gpmi
> and try again.
> I am sure that you did not configure the PADs correctly.
> Huang Shijie
knowing that it was not normal to have NANDF_CS1 toggling made me think
to look more closely at the hardware level, and I found that the 8 data
lines are unfortunately inverted on our PCB.
I have temporarily patched the Linux GPMI driver to invert LSB and MSBs
for read and writes, and voilà, now my NAND flash is correctly detected!
Sorry for the noise.
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