From: Lenny <leonhard.neuh...@gmail.com> Reply-To: "beagleboard@googlegroups.com" <beagleboard@googlegroups.com> Date: Wednesday, July 23, 2014 at 10:29 AM To: "beagleboard@googlegroups.com" <beagleboard@googlegroups.com> Cc: <sun19920...@gmail.com> 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, sun19...@gmail.com 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 beagleboard+unsubscr...@googlegroups.com. > 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 beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
