From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sergey Yanovich Date: Tue, 21 May 2013 15:23:34 +0400 Subject: [U-Boot] [PATCH] arm: pxa: PXA270 D-Cache as ram In-Reply-To: <201305211254.59982.marex@denx.de> References: <1369087586-1344-1-git-send-email-ynvich@gmail.com> <201305211239.52671.marex@denx.de> <1369132962.20319.3.camel@host5.omatika.ru> <201305211254.59982.marex@denx.de> Message-ID: <1369135414.12900.3.camel@host5.omatika.ru> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.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.