[U-Boot] Atmel SAMA5D31 NOR boot - sanity check required

[Andy Pont]

Hello!

I am currently working on an implementation of NOR boot support for the
Atmel SAMA5D31-EK reference platform as a precursor to a custom hardware
platform.  When tested and working I will push the support back to the
community but what I have at the moment doesn't appear to do anything so I
would appreciate a sanity check on the work done so far.  

For reference the documentation for the Atmel SoC says:

If BMS signal is tied to 0, BMS_BIT is read at 1.  The ROM code allows
execution of the code contained in the memory connected to Chip Select 0 of
the External Bus Interface (J828F128P33TF70A) and then goes on to detail the
startup mode and changes that need to be made to the PLL and SMC.

For simplicity sake, I have taken the standard SAMA5D31-EK configuration of
SPL+U-Boot and have added NOR boot support to SPL based on one of the other
boards.  The board header file has the following configuration:

#define CONFIG_SPL_NOR_SUPPORT
#define CONFIG_SYS_FLASH_CFI            1
#define CONFIG_FLASH_CFI_DRIVER         1
#define CONFIG_SYS_FLASH_BASE           0x00000000
#define CONFIG_SYS_MONITOR_BASE         CONFIG_SYS_FLASH_BASE

As per the standard SPL build for this hardware platform the
CONFIG_SYS_INIT_SP_ADDR value is set to 0x310000 but I haven't found a
definitive statement that confirms that the internal SRAM is mapped to that
location when in this boot mode.

So my questions are...

Is the SPL+U-Boot implementation the best way for NOR booting or should it
all just be built as a single U-Boot image?

Do the settings above look correct, particularly the value for the initial
stack pointer?

How best do I debug SPL to determine where it is getting lost in the weeds?

Many thanks,

Andy.