Dear Marek Vasut,
On Tue, 2013-05-21 at 12:54 +0200, Marek Vasut wrote:
SRAM is just the in-CPU bit of fast RAM. What do you mean by "battery-backup" ?
Yes, you are right. It is 'for high speed code or data storage preserved during low-power states' using a quote from PXA270 EMTS (top of page 1). Battery-backup is optional. I mixed PXA270 and LP-8x4x specs.
It can be used as a ultra-fast persistent storage in OS. Wasting a quater of it just to boot the system isn't the best choice.
The SRAM is used for stack in U-Boot until you leave board_init_f, then the stack is relocated to DRAM. The OS can use SRAM as needed, U-Boot is no longer operational once you load subsequent OS. What's the problem?
Anyway, SRAM preserves its state when power is off. Poweroff time could be in years with a backup battery. In addition, D-Cache is an order of magnitude faster than SRAM (approx. 9 times) for both reads and writes.