Hi Marc-André, On Tue, Nov 16, 2010 at 17:38:20, Marc-André Hébert wrote: > Hi, > > I have 2 OMAPL138/AM1808 boards: one with mDDR and ther other with > SDRAM. I am looking at options to reduce power consumption. One the of > options we are looking into is the cpu frequency. Not having a lot of > success with the SDRAM board. Here is a little list of what I tried > (with the Arago tree). > > 1) I have tried enabling the cpu frequency scaling. It works with the > mDDR board but any change in frequency fails when using the SDRAM > board. I am guessing this is because the DDR is derived from PLL1 > while the SDRAM uses PLL0. Is there a way to make the cpu frequency > work or is this impossible with SDRAM?
This is something that is better clarified on the OMAP-L1 forum on e2e.ti.com, but I don't see why SDRAM cannot be connected to the same external memory interface that mDDR connects to and thus be insulated from PLL0 changes too. > > 2) With the SDRAM board, I then tried downclocking the cpu directly in > the bootloader using the AISgen utility. Under the PLL0 tab, I > modified by DIV1 from 1 to 2 to operate the CPU at 150Mhz instead of > 300Mhz while preserving my SDRAM at 100Mhz. With this, the kernel > hangs at boot during the SATA initialization (I can reach the console > fine if I disable the AHCI). I looked at the SATA controller datasheet > but couldn't find a link between the SYSCLK1 and the SATA (since DIV1 > affects SYSCLK1, right?). Why not use the cpufreq driver in kernel? Some usage information is available here: http://processors.wiki.ti.com/index.php/OMAP-L1_Linux_Drivers_Usage#CPUFreq > > 3) Similar to #2, I changed the PLL0 settings post-divider (2 to 3) > and div3 (3 to 2). This gave me CPU 200 Mhz (with settings matching > what is found under da850_opp_200 in da850.c) and still keeping the > 100Mhz SDRAM. This configuration stalls during the kernel boot right > after the reset of unused clocks. Hmm, no idea on this one. Thanks, Sekhar _______________________________________________ Davinci-linux-open-source mailing list [email protected] http://linux.davincidsp.com/mailman/listinfo/davinci-linux-open-source
