From: <[email protected]> Reply-To: "[email protected]" <[email protected]> Date: Wednesday, July 23, 2014 at 12:21 PM To: "[email protected]" <[email protected]> Subject: Re: [beagleboard] Re: How to synchronize ADC sampling clock ？
> Hi, John, > could you specify which 1MHz timer ? I just know 24MHz clock for ADC... > About synchronization, I will try to synchronize ADC(with PRU as Lenny said) > to PTP clock (on CPTS, common platform time sync) rather than kernel system > clock. > Do you have experience handling CPTS? I am not sure if CPTS driver has > ability of triggering other hardware unit (software trigger), and what its > accuracy of synchronization is. Have you looked at this: http://processors.wiki.ti.com/index.php/TI81XX_PSP_Ethernet_Switch_User_Guid e#IEEE_1588.2F802.1AS_PTP_Support Regards, John > > > Thanks. > > > > john3909於 2014年7月24日星期四UTC+8上午1時43分56秒寫道： >> >> From: Lenny <[email protected] <javascript:> > >> Reply-To: "[email protected] <javascript:> " >> <[email protected] <javascript:> > >> Date: Wednesday, July 23, 2014 at 10:29 AM >> To: "[email protected] <javascript:> " <[email protected] >> <javascript:> > >> Cc: <[email protected] <javascript:> > >> Subject: [beagleboard] Re: How to synchronize ADC sampling clock ？ >> >>> Hi, >>> >>> if you control the ADC from the PRU, you can use the ADC in >>> single-acquisition mode and perform a new acquisition every 200 PRU cycles >>> (every microsecond) for example (or whatever repetition rate you want), and >>> therefore use the 200 MHz PRU clock as a low-jitter timer. This way you can >>> have jitter values well below one microsecond. You should also be able to >>> synchronize the PRU with an external clock on one of its input pins leading >>> to the r31 register if that is still needed. >>> >>> There should probably be a residual timing jitter of maximally 1/24MHz (ca. >>> 42ns) because (as far as i know, but im not sure) the 24 MHz ADC sampling >>> clock is not intrinsically synchronized with the 200 MHz PRU clock, so once >>> the PRU launches a new acquisition, it won't take place before the ADC clock >>> starts a new cycle. I did not find any documentation on how the PRU and ADC >>> clock signals are derived in the hardware, that is if they come from the >>> master clock or not, but i did experimentally observe a jitter of a few >>> percent of a microsecond. >>> >>> If you want I can send you some code examples. >> That sounds like a good solutions. Also, you could use a 1MHz timer which you >> can synchronize to the PTP clock and then just average the ADC samples >> received since the last clock interrupt. >> >> Regards, >> John >>> >>> >>> Lenny >>> >>> >>> >>> On Tuesday, July 22, 2014 8:08:39 AM UTC+2, [email protected] wrote: >>>> Hi, >>>> how to synchronize ADC sampling clock (CLK_M_OSC, in AM335x manual, page >>>> 3731) with external 1PPS source or others? >>>> I used PTP to synchronize system clock in the kernel before, however, the >>>> jitter is about 30us （but I need a jitter with accuracy under 1us.）. >>>> So I want to synchronize ADC sampling clock(24MHz), Is there any way to >>>> synchronize it ? Is the clock of CLK_M_OSC be adjustable? >>>> Thanks. >>> -- >>> 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] <javascript:> . >>> 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]. > 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]. For more options, visit https://groups.google.com/d/optout.
