On Fri, Nov 09, 2012 at 06:25:49, Hunter, Jon wrote: > > On 11/08/2012 12:06 PM, Hiremath, Vaibhav wrote: > > On Thu, Nov 08, 2012 at 23:28:53, Hunter, Jon wrote: > >> > >> On 11/08/2012 11:47 AM, Hiremath, Vaibhav wrote: > >>> On Thu, Nov 08, 2012 at 23:09:57, Hunter, Jon wrote: > >> > >> [snip] > >> > >>>> I think you are missing the point here. For OMAP devices we have two > >>>> main external clock sources which are the 32kHz clock and the sys_clk > >>>> (can be a range of frequencies from 12-38.4MHz for OMAP4). The point is > >>>> for OMAP these clock sources are always present and AFAIK there is no > >>>> h/w configuration that allows you not to have the 32kHz clock source. > >>>> PRCM needs it and I think for OMAP1 the reset logic needs it (if memory > >>>> serves). > >>>> > >>>> Igor was mentioning a h/w scenario where the 32kHz source is not > >>>> present. However, I am not sure which devices support this and is > >>>> applicable too. > >>>> > >>>> So we are not discussing the 32k-sync-timer here. We are discussing > >>>> whether there are any device configurations where a 32k clock source > >>>> would not be available for the gptimer. > >>>> > >>> > >>> Exactly that is the point I am trying to make here, > >>> > >>> In case of AM33xx, it is certainly possible to build the system without > >>> this 32Khz clock. > >>> > >>> Interesting point here is, this 32KHz clock is external clock coming from > >>> crystal connected to in-built RTC module. > >> > >> Thanks. Looking at the AM3358 data manual it states ... > >> > >> "The OSC1 oscillator provides a 32.768-kHz reference clock to the > >> real-time clock (RTC) and is connected to the RTC_XTALIN and RTC_XTALOUT > >> terminals. OSC1 is disabled by default after power is applied. This > >> clock input is optional and may not be required if the RTC is configured > >> to receive a clock from the internal 32k RC oscillator (CLK_RC32K) or > >> peripheral PLL (CLK_32KHZ) which receives a reference clock from the > >> OSC0 input." > >> > >> So what is clear to me that an external 32k clock source is optional. > >> However, it still appears that you will always have an internal 32k > >> source and so regardless of the h/w configuration, a gptimer will always > >> have an 32k clock available on the AM335x devices. Is that correct? > >> > > > > Internal RC oscillator is not accurate at all, so not guaranteed to give > > accurate 32.768Hz clock. The oscillation band is from 16Khz to 64Khz. > > > > So it may not be useful as a system clocks, right? > > By the way, according to the AM3358 data manual (paragraph above), even > if there is no external 32k clock source and if you don't use the > internal 32k oscillator, you can still generate a 32k clock from the PER > PLL (CLK_32KHZ). So therefore, there should always be a 32k clock source > available for the gptimer. Is that correct? Yes that's correct, but it is from PER domain, so duging suspend time, it will be disabled. This can not be treated as a persistent clock. > > At the end of the day, I am just trying to understand if any OMAP/AM > device supports a h/w configuration where there is no 32k clock source > available for the gptimer. > I know and completely understand. We need to come up with solution which works on all platforms. Thanks, Vaibhav -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
