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From: Sergey Yanovich <ynvich@gmail.com>
To: u-boot@lists.denx.de
Subject: [U-Boot] [PATCH] arm: pxa: PXA270 D-Cache as ram
Date: Tue, 21 May 2013 15:23:34 +0400	[thread overview]
Message-ID: <1369135414.12900.3.camel@host5.omatika.ru> (raw)
In-Reply-To: <201305211254.59982.marex@denx.de>

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.

  reply	other threads:[~2013-05-21 11:23 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-05-20 22:06 [U-Boot] [PATCH] arm: pxa: PXA270 D-Cache as ram Sergey Yanovich
2013-05-21 10:39 ` Marek Vasut
2013-05-21 10:42   ` Sergey Yanovich
2013-05-21 10:54     ` Marek Vasut
2013-05-21 11:23       ` Sergey Yanovich [this message]
2013-05-21 11:38         ` Marek Vasut
2013-05-21 11:56           ` Sergey Yanovich
2013-05-21 15:00             ` Marek Vasut
2013-05-21 16:31               ` Sergey Yanovich
2013-05-21 19:02                 ` Marek Vasut
2013-05-21 19:18                   ` Sergey Yanovich
2013-05-21 19:24                     ` Marek Vasut
2013-05-21 19:42                       ` Sergey Yanovich
2013-05-21 20:07                         ` Marek Vasut
2013-05-21 20:24                           ` Sergey Yanovich
2013-05-21 21:38                             ` Marek Vasut
2013-05-22 13:02                               ` Sergey Yanovich
2013-05-22 13:04                                 ` Marek Vasut
2013-05-22 13:21                                   ` Sergey Yanovich
2013-05-22 13:54                                     ` Marek Vasut
2013-05-23 17:43                               ` Mike Dunn

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