> On Apr 15, 2017, at 6:49 AM, Rathin Dholakia <rathindhola...@gmail.com> wrote: > > Dear John, > > Thanks for your suggestion. Yes I was thinking in same line but bit > differently. I am still a rookie in all this so have few queries in your > approach if you can clarify. > > 1. Instead of PRU as oscillator, I was planning to use one of the 4 onboard > timers. Wont it be better? why didyou suggested PRU instead of Timer? some > benefit? It depends on your absolute time accuracy requirements. If you are looking at 100mS accuracy, then by all means use the Timer with interrupts given the interrupt latency of Linux. If you want 1uS accuracy, then you need a disciplined oscillator which drives a 1MHz counter which can be read by the PRU so that you can time tag the ADC samples. > > 2. My ADC chip (AD7864) has an inbuilt ring output ring register with circles > among the outputs of 4 channels every time I pull down "READ" pin. So, do I > still need a FIFO? DMA has to arbitrate for bus access and isn’t efficient if you are only reading one or just a few samples at a time. You want to read at least 32 samples at a time to make DMA viable; hence you want a FIFO of at least 64 samples with an interrupt that occurs when the FIFO is almost full. > > 3. Why SPI? wont 12 Digital parallel pin faster? and BBB uses pin addresses > then how is DMA different from normal GPIO access? Because the SPI driver already supports DMA transfers. > > 4. For utilizing PRU, are you recommending ASM coding or normal C coding > using some library? I ham bit reluctant because of the assembly coding > involved because I am not that good at it, yet! It doesn’t matter, both will work just fine.
> > Thanks a ton, > Rathin > > My approach in brief for people's feedback: > 1. Use Timer Interrupt using on-board timer periodically for generating SOC > 2. Detect EOC using interrupt from ADC, initiate read cycle (ISR) for all 4 > channels The processor overhead for 100ksps will mean the CPU will be running at close to 60% just to service the interrupts. Not a good idea. Using DMA, CPU will be less than 3%. > 3. second interrupt watching 1PPS from GPS, which would reset the Timer > period (as disciplining sampling) First, the timer is derived from the CPU PLL which multiplies the CPU crystal oscillator. The frequency error can be 2 to 3%. Add to that the Interrupt Latency of Linux, and your timing error will be bad. Also remember that the timing error is accumulative so you will continue to see time drift. Temperature changes will affect the crystal frequency as well. > 4. Use pipe for passing each buffer to DFT. > 5. Use the timing info from UART to time-stamp the DFT output Timing needs to be done way before you communicate this info. UART have significant latency as well. Regards, John > > > > On Sat, Apr 15, 2017 at 4:38 AM, John Syne <john3...@gmail.com > <mailto:john3...@gmail.com>> wrote: > I recommend that you look for a external ADC with a sample FIFO, then the > samples are measured at predefined intervals and you could read them with the > ARM processor and use the PRU for your timing requirements. I take it you > will need a disciplined oscillator sync’d to the GPS 1pps, which can be done > with the PRU. Using an ADC with SPI interface and FIFO means you could use > DMA to transfer the samples, freeing up the CPU for more important work. > > Regards, > John > > > > >> On Apr 14, 2017, at 12:46 PM, Rathin Dholakia <rathindhola...@gmail.com >> <mailto:rathindhola...@gmail.com>> wrote: >> >> Hello TJF, >> >> Thanks for your suggestion, to clarify my side further, let me elaborate. >> >> >> My requirement is 256 (samples per Cycle) * 50(cycles, power frequency) * 6 >> (channels) = 76.8 k SPS >> >> So I need overall 100k(rounded off) 100k sampling. >> >> And my input signal is between +- 10 Volts and I don't want to scale for >> resolution purposes. Apart from that I need dedicated ADC for each channels >> so I'll prefer separate ADC chip. >> Does this make sense? Or I am wrong? >> >> Thanks >> >> On Friday, April 14, 2017, TJF <jeli.freih...@gmail.com >> <mailto:jeli.freih...@gmail.com>> wrote: >> Hi Rathin! >> >> Am Freitag, 14. April 2017 16:58:58 UTC+2 schrieb Rathin Dholakia: >> I am willing to interface, 12 bit 4 channel, Simultaneous Sampling >> High-Speed ADC (Analog AD7864 >> <http://www.analog.com/media/en/technical-documentation/data-sheets/AD7864.pdf>) >> to BeagleBone Black, and operate it at 100k sampling rate. My present >> thoughts are to use header P8 Digital I/O pins to control the ADC as well as >> to read the input data from the ADC (using interrupt(s) - EOC). I will also >> do a DFT on the received data samples. >> >> Your target isn't very clear. Do you mean 100 k overall sampling rate (2 x >> 25 k)? In this case you could use the internal ADC (up to 4 x 50 k sampling >> rate, 0-1V8). Otherwise you'll need the external. >> >> Anyway, it should be possible when you fetch the samples by one PRU, and use >> the other for DFT. Slow tasks can run on the ARM under Linux. >> >> Regards >> >> -- >> For more options, visit http://beagleboard.org/discuss >> <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/ZufgBytqkOI/unsubscribe >> <https://groups.google.com/d/topic/beagleboard/ZufgBytqkOI/unsubscribe>. >> To unsubscribe from this group and all its topics, send an email to >> <>beagleboard+unsubscribe@ >> <mailto:beagleboard+unsubscr...@googlegroups.com>googlegroups.com >> <mailto:beagleboard+unsubscr...@googlegroups.com>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/beagleboard/7f5699a8-b6ab-4e96-8fa2-18cc8343755e%40googlegroups.com >> >> <https://groups.google.com/d/msgid/beagleboard/7f5699a8-b6ab-4e96-8fa2-18cc8343755e%40googlegroups.com?utm_medium=email&utm_source=footer>. >> For more options, visit https://groups.google.com/d/optout >> <https://groups.google.com/d/optout>. >> >> >> -- >> Rathin A. Dholakia >> "Dont GO through life, GROW through life" >> >> >> -- >> For more options, visit http://beagleboard.org/discuss >> <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 >> <mailto:beagleboard+unsubscr...@googlegroups.com>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/beagleboard/CAJW6HtQV0Q0hEP9hy8%2BO%3DACnNU1pvjZOrLnt_xyoH-SDXLMNMQ%40mail.gmail.com >> >> <https://groups.google.com/d/msgid/beagleboard/CAJW6HtQV0Q0hEP9hy8%2BO%3DACnNU1pvjZOrLnt_xyoH-SDXLMNMQ%40mail.gmail.com?utm_medium=email&utm_source=footer>. >> For more options, visit https://groups.google.com/d/optout >> <https://groups.google.com/d/optout>. > > > -- > For more options, visit http://beagleboard.org/discuss > <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/ZufgBytqkOI/unsubscribe > <https://groups.google.com/d/topic/beagleboard/ZufgBytqkOI/unsubscribe>. > To unsubscribe from this group and all its topics, send an email to > beagleboard+unsubscr...@googlegroups.com > <mailto:beagleboard+unsubscr...@googlegroups.com>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/3879F2CA-33BA-444A-A055-A8C9290C6E3C%40gmail.com > > <https://groups.google.com/d/msgid/beagleboard/3879F2CA-33BA-444A-A055-A8C9290C6E3C%40gmail.com?utm_medium=email&utm_source=footer>. > > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. > > > > -- > Rathin A. Dholakia > "Dont GO through life, GROW through life" > > -- > For more options, visit http://beagleboard.org/discuss > <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 > <mailto:beagleboard+unsubscr...@googlegroups.com>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/CAJW6HtRkpx5AFTVS4TO%2BRxMExenSKSpHMHTPWCLydwXpZqFyAQ%40mail.gmail.com > > <https://groups.google.com/d/msgid/beagleboard/CAJW6HtRkpx5AFTVS4TO%2BRxMExenSKSpHMHTPWCLydwXpZqFyAQ%40mail.gmail.com?utm_medium=email&utm_source=footer>. > For more options, visit https://groups.google.com/d/optout > <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. 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