[Buildroot] [PATCH] board: add support for Freescale i.MX6UL Evaluation Kit

[Julien Boibessot <julien.boibessot@free.fr>]

Thomas,

On 21/01/2016 13:32, Thomas Petazzoni wrote:
> Julien,
>
> On Thu, 21 Jan 2016 12:40:39 +0100, Julien Boibessot wrote:
>
>> I first started to use genimage, yes, but as I wanted to mimic Freescale
>> microSD partitionning I was stucked by the fact that genimage
>> (apparently) doesn't handle VFAT partitions. Indeed i.MX6UL microSD
>> Freescale's format is:
>> * 1MB free
>> * U-Boot
>> * VFAT partition starting at offset 8M to store kernel and dtbs (size 16MB)
>> * EXT2 rootfs on the remaining space.
>>
>> So I ended up in using i.XM28EVK way of doing
>> (board/freescale/imx28evk/create-boot-sd.sh).
>> Do you agree ?
> genimage is perfectly capable of creating a vfat partition, see
> board/raspberrypi/genimage-raspberrypi.cfg for an example.

cool ! Is that new ?
I will adapt my patch accordingly.

>
>>> Why ? Any reason to use EABI over EABIhf, which is now the default in
>>> Buildroot for Cortex-A processors ?
>> Well i.MX6UL has no VFPU, only a NEON, so I thought it was a good idea,
>> no ? :-)
> What is your source for this information, because it seems to be wrong.

Well I was relying on Freescale/NXP fact sheets at:
   
http://www.nxp.com/products/microcontrollers-and-processors/arm-processors/i.mx-applications-processors-based-on-arm-cores/i.mx-6-processors/i.mx6qp/i.mx-6ultralite-processor-low-power-secure-arm-cortex-a7-core:i.MX6UL

and didn't dig more than that. My fault !

> According to ARM
> (http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0463f/index.html):
>
> """
> The Cortex-A7 MPCore processor implements the ARMv7-A architecture with
> the following architecture extensions:
> [...]
>  - Vector Floating-Point version 4 (VFPv4) architecture extension for
>    floating-point computation that is fully compliant with the IEEE 754
>    standard.
> """
>
> So, the Cortex-A7 (which is the core used in the i.MX6UL) has a
> mandatory VFPv4 unit.
>
> Also, according to Freescale
> (http://cache.nxp.com/files/32bit/doc/fact_sheet/IMX6SRSFS.pdf), in
> the column for i.MX6UL:
>
> """
> 128 KB L2 cache, NEON?, VFP, TrustZone?
> """
>
> So, please use BR2_EABIHF, and improve your systems by using hard-float
> instead of soft-float :-)

No problemo ! Can you recommend a test tool to evaluate Floating point
performances inside BR ?

Thanks for your review.

Best regards,
Julien