On 11/08/2012 12:28 PM, Hiremath, Vaibhav wrote: > On Thu, Nov 08, 2012 at 23:43:31, 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? >> >> So I admit I am not familiar with the details on the AMxxxx stuff side >> so much. >> >> So maybe I should ask this question ... >> >> Do you support a configuration where there is no external 32k clock AND >> the internal oscillator and hence, RTC are not used? >> > > Why not, you could give-up on persistent time across suspend/resume and use > OSC clock as a input clock to timer. > > And the timer code, which we have we have added fallback mechanism for this, > First make sure that timer is properly set for RTC32K, if yes, then use it, > and if no, then fall back to OSC clock. You mean sync-32k and not rtc32k right? We are just detecting the presence of the sync-32k counter and if so use it, otherwise use a gptimer. >> I would have expected that you would always want the RTC running, but if >> you are saying that you don't require an external 32k and the internal >> 32k is not accurate, then I assume that having the RTC available is not >> mandatory either. >> > > Yes, it is not mandatory, considering fact that, you will not have > persistent time and other low-power modes. > Actually it depends on board/EVM use-case, right? Yes absolutely, just trying to understand if that is a valid use-case or not. So for AM33xx the external 32k is not mandatory. Thanks. Jon -- 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
