Ah, very interesting. > dmesg | grep clock [ 0.000000] OMAP clockevent source: GPTIMER1 at 32768 Hz [ 0.000000] sched_clock: 32 bits at 32kHz, resolution 30517ns, wraps every 131071999ms [ 0.309448] omap_hwmod: l4_div_ck: missing clockdomain for l4_div_ck. [ 0.716979] Skipping twl internal clock init and using bootloader value (unknown osc rate) [ 1.001129] Switching to clocksource 32k_counter [ 6.907501] twl_rtc twl_rtc: setting system clock to 2000-01-01 00:00:01 UTC (946684801)
Do you recommend using "Get linaro image tools: method 2 (source code)" ( http://releases.linaro.org/12.01/ubuntu/leb-panda/ ) and building the kernel myself? I think we're, for the most part, unconcerned with power usage for our application (we're robotics researchers and, I believe, computation is only a small fraction of the power draw when compared to the motors). It seems to me that we would want to disable some of the power-saving changes that have been made, such as this timer, and possibly configure other settings like cache behavior, though I have no idea how they're currently set. I have a bunch of docs from ARM on power and cache config, but I haven't messed around with them as I'm not sure where to start. My best guess is that I would have to rebuild the kernel to start handling that configuration myself. Is that true? Some people ( http://groups.google.com/group/pandaboard/browse_thread/thread/a18fa3514d130720 ) have mentioned enabling line fill and prefetching to speed up memcpy operations, which also seems useful. Is this also a kernel-level setting? If you think that's the right route, I would appreciate advice on where, within the build process, I need to start changing things to get the settings I want. Many thanks, Andrew On Feb 8, 2012, at 12:21 AM, Dmitry Antipov wrote: > On 02/07/2012 02:43 PM, Andrew Richardson wrote: > >> I'm experiencing what appears to be a minimum clock resolution issue >> in using clock_gettime() on a PandaBoard ES running ubuntu. > > Do you have CONFIG_OMAP_32K_TIMER enabled in your kernel? > Look at 'dmesg | grep clock' and check for the following: > > ... > OMAP clockevent source: GPTIMER1 at 32768 Hz > sched_clock: 32 bits at 32kHz, resolution 30517ns, wraps every 131071999ms > ... > > Most probably this is the answer - by default, recent OMAPs are configured > to use less-accurate, but more energy-saving timer (32KHz) in favor of > MPU timer. > > Disable CONFIG_OMAP_32K_TIMER to switch to MPU timer, and check > 'dmesg | grep clock' to see: > > ... > OMAP clockevent source: GPTIMER1 at 38400000 Hz > OMAP clocksource: GPTIMER2 at 38400000 Hz > sched_clock: 32 bits at 38MHz, resolution 26ns, wraps every 111848ms > ... > > BTW, I have no ideas why clock_getres(CLOCK_REALTIME,...) returns {0, 1} > regardless of underlying clock source. I expect {0, 30517} for 32K timer > and {0, 26} for MPU timer. > > Dmitry > >
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