You may find this tool from TI useful: http://processors.wiki.ti.com/index.php/AM335x_Clock_Tree_Tool
On Saturday, April 29, 2017 at 10:14:31 PM UTC+3, Justin Pearson wrote: > > Thanks Graham. What do you mean by "check and verify the clock tree > behavior"? I searched the TRM for "clock tree" but I'm still not sure how > to figure out which timers make their way through various PLLs to the PRU > and main CPU. > > > > On Wed, Apr 26, 2017 at 10:00 AM, Graham <[email protected] > <javascript:>> wrote: > >> Well, best way is to read the schematic. (BBB Rev C schematic, dated >> March 21, 2014) >> 24 MHz Sitara clock crystal is on upper left of page 3, hooked to main >> oscillator I/O. >> There is also a 32 kHz crystal shown there for the Real Time Clock. >> >> The 25 MHz crystal is on page 9, hooked to the LAN8710, which is the >> Ethernet PHI. >> >> I am not a PRU expert, but I don't think there is, or should be, a fixed >> relationship between >> the PRU clock and the CPU clock. The CPU in a Sitara is a variable speed >> CPU, and >> can run anywhere from a few hundred MHz to a GHz, depending on loading, >> and it is under kernel control. >> >> I would not think you would want the 200 MHz clock for the PRU to be >> variable >> like that, since it would totally destroy the real time advantage of the >> PRU. >> >> So, I suspect that the clock for the PRU is a fixed clock coming from a >> different >> place in the clock tree than the variable speed CPU. >> >> You should really check and verify the clock tree behavior. >> >> --- Graham >> >> == >> >> On Wednesday, April 26, 2017 at 8:02:38 AM UTC-5, Justin Pearson wrote: >>> >>> Thanks Graham. Follow-up questions: >>> >>> 1. Where exactly did you find this information? I looked through the TRM >>> and SRM but couldn't find anything definitive. >>> >>> 2. Is the 200-MHz PRU driven from the same 24 MHz oscillator that drives >>> the CPU? If so, is it correct that the PRU cycle counter increments >>> precisely once for every 5 CPU cycles? >>> >>> Thanks for your help. >>> -Justin >>> >>> On Tuesday, April 25, 2017 at 7:35:19 PM UTC-7, Graham wrote: >>>> >>>> The CPU in a BBB runs from a 24 MHz Oscillator. >>>> There is a 25 MHz oscillator on the board, but that is for the Ethernet. >>>> --- Graham >>>> >>>> == >>>> >>>> On Tuesday, April 25, 2017 at 7:09:50 PM UTC-5, Justin Pearson wrote: >>>>> >>>>> How can I find out whether the PRU and CPU are driven by the same >>>>> oscillator? Specifically, a colleague told me that the IEP timer (which >>>>> I'm >>>>> reading with the PRU) is driven by a 24 MHz oscillator that's PLL'd so >>>>> the >>>>> timer increments at 200 MHz, whereas the CPU is driven by a 25 MHz >>>>> oscillator PLL'd so that the CPU runs at 1 GHz. >>>>> >>>>> It seems to me that if they're driven by different oscillators, then >>>>> they could drift apart over time. >>>>> >>>>> Page 1177 of the TRM (spruh73n.pdf) mentions a 32-kHz crystal >>>>> oscillator, but I don't see how that's related. >>>>> >>>>> Also, are these oscillators within the Sitara SoC, or somewhere else >>>>> on the BBB? The SRM just references 24.576 MHz oscillator (pg 70 of e14 >>>>> BBB_SRM_rev 0.9.pdf), and I'm not sure how that's related to the 24/25 >>>>> MHz >>>>> oscillators my colleague mentioned. >>>>> >>>>> Thanks for your help. >>>>> >>>>> -- >> For more options, visit http://beagleboard.org/discuss >> --- >> You received this message because you are subscribed to a topic in the >> Google Groups "BeagleBoard" group. >> To unsubscribe from this topic, visit >> https://groups.google.com/d/topic/beagleboard/XFv4Ha4RbD4/unsubscribe. >> To unsubscribe from this group and all its topics, send an email to >> [email protected] <javascript:>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/beagleboard/843f0f74-584e-440d-828f-df0cd61d1e1b%40googlegroups.com >> >> <https://groups.google.com/d/msgid/beagleboard/843f0f74-584e-440d-828f-df0cd61d1e1b%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> >> For more options, visit https://groups.google.com/d/optout. >> > > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/5c7e6721-1075-4d6e-a69e-bc38f3409592%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
