[U-Boot] Question on the max size of SPL and OMAP3 SRAM

[Ash Charles]

Hi Tom,
On Wed, Feb 18, 2015 at 10:32 AM, Tom Rini <trini at ti.com> wrote:
> Well, the best answer is to check the TRM and see what it says about the
> ROM memory map.  My recollection is that 0x40200800 - 0x4020BBFF is the
> download area and 0x4020E000 - 0x4020FFFC is what it calls the public
> stack and we decide to use it for our stack (rather than keeping it in
> the download area).  The range inbetween (0x4020BC00 - 0x4020DFFF) is
> claimed by the ROM and we shouldn't touch it.
I just had a look at the "64KB RAM Memory Map of GP Devices" in the
TRMs for AM/DM37xx, and OMAP3530.

The download area starts out 0x4020 0000---I can't find any history on
the 0x800 offset to 0x40200800 (the value comes from some very early
x-loader commits).  Moving CONFIG_SPL_TEXT_BASE to 0x4020 0000 buys 2
kB extra and seems (lightly tested) to work okay on a couple different
Overos.

According to the TRM, the download area extends up to 0x4020 F000
followed by a ~3 kB public stack from 0x4020F000 to 0x4020FCB0.  The
area between 0x4020FCB0 and 0x4020FFF contains 'reserved', 'tracing
data', and 'RAM exception vectors' sections---I'm guessing these are
fair game as these are just how the ROM code chooses to use the
memory?

Looking at doc/SPL/README.omap3, both possible configurations match
your email i.e.
0x40200800 - 0x4020BBFF: Area for SPL text, data and rodata
0x4020E000 - 0x4020FFFC: Area for the SPL stack.

Based on u-boot-spl.lds though, I think the first area would be
[CONFIG_SPL_TEXT_BASE - (CONFIG_SPL_TEXT_BASE + CONFIG_SPL_MAX_SIZE)]
(default: 0x40200800 - 0x4020e000)

The stack seems to be defined by CONFIG_SPL_STACK used in
arch/arm/lib/crt0.S.  On most platforms, this seems to point to an
area in SDRAM, not SRAM.  How can this work before RAM is setup?

In short: does this seem reasonable?
#define CONFIG_SPL_TEXT_BASE 0x40200000
#define CONFIG_SPL_MAX_SIZE (64*1024)

Thanks for any insight,
--Ash