Yes, I can setup a oscillator circuit, in fact my GPS board provides me 10 MHz oscillator output which is extremely stable, I can use that along with PRU (thanks for the tip).
And yes, completely agree, I am reconsidering my ADC choice, that would ease up my design many folds. And I am also trying out TI's 4.4-rt- kernel for reducing my overall latency. I will document things here once I proceed a little, So others can also use it in future :) I cant thank you enough, John! On Mon, Apr 17, 2017 at 1:53 AM, John Syne <john3...@gmail.com> wrote: > > On Apr 16, 2017, at 6:20 AM, Rathin Dholakia <rathindhola...@gmail.com> > wrote: > > Dear John, > > Ok, now I understood. So basically, I have to create a dedicated crystal > based oscillator for time reference. I though you were telling to use PRU > for that, sorry my bad. > > Well, you can use the PRU as part of the PLL. Use the PRU to read the > counter when the 1pps signal occurs. If the count is less than 1,000, > increase the voltage from the DAC or decrease the DAC voltage if the count > is higher than 1,000. The DAC voltage is controlling the VXCO (Voltage > Controlled Crystal Oscillator). Typically the VXCO run at several MHz, you > you need to divide that down to generate a 1MHz clock. The counter is reset > to zero after reading the count. > > > Though I'll have to figure out some way to convert my parallel digital > outputs in to SPI compatible serial signals and also how to control ADC, > FIFO and SPI all to gather. but that I will search! and will post here > > Once again thanks and will tell you if there is some query. > > > Apart from that Can you suggest some soultion to convert my parallel ADC > output > > Why not use a ADC with a SPI interface? If you really want to use a > parallel ADC, then GreenPAK has a nice solution. > > http://www.silego.com/products/402/312/AN-1083.html > > > Regards, > John > > > On Sunday, April 16, 2017 at 2:40:48 AM UTC+5:30, john3909 wrote: >> >> >> On Apr 15, 2017, at 1:06 PM, Rathin Dholakia <rathind...@gmail.com> >> wrote: >> >> Dear John, >> >> Thanks a lot for such a detailed insight! >> >> Yes I will need a precise time,and I was misinformed about the timer so I >> was under impression that they are the clock source and hence driving >> force. >> >> I will need some time to think and digest all but before I proceed let me >> rephrase what I have understood, so that you can correct me: >> >> - Use PRU0 as an timer (oscillator) for deriving SOC >> - Use PRU1 for DMA using SPI via FIFO, and also to time tag!? >> >> Use ARM SPI driver for reading ADC samples via EDMA, but use PRU1 to >> monitor the EDMA completion and then using the value from the 1MHz counter, >> time tag the ADC buffer. You don’t have to tag each sample because you know >> the sampling rate. >> >> - Remaining ARM processor for DFT and other thing >> >> Did I get it correctly? >> >> But then my question are: >> 1. I still need to detect EOC and assert READ signals then how will my >> FIFO or DMA free my processor? >> >> Not necessary as the FIFO half full will cause an interrupt and initiate >> the DMA transfer. >> >> 2. My PRU 1MHz, How can it be disciplined, it will still need an >> interrupt to detect 1PPS right? >> >> The 1pps is used with a PLL (phase lock loop) to tune the 1MHz crystal >> frequency so that the 1MHz is exactly 1MHz. In the case that the GPS is >> lost, the Oscillator continues to be accurate for several hours or more. >> >> 3. And How can it replace Time data from GPS? >> >> Same answer as above. >> >> >> Pardon me if above question sound novice! I have not worked on it before. >> >> Maybe you are suggesting something like this: >> 1. http://processors.wiki.ti.com/index.php/PRU_Linux-based_Exam >> ple_Code#PRU_edmaConfig >> >> This example is a good one to show you how to monitor the EDMA transfer >> completion with the PRU. >> >> 2. https://groups.google.com/forum/#!topic/beagleboard/UPbU2WoVzVI >> >> >> Regards, >> John >> >> >> On Sat, Apr 15, 2017 at 8:13 PM, John Syne <john...@gmail.com> wrote: >> >>> >>> On Apr 15, 2017, at 6:49 AM, Rathin Dholakia <rathind...@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 <john...@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 <rathind...@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.f...@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 >>>>> --- >>>>> 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.co >>>>> m/d/topic/beagleboard/ZufgBytqkOI/unsubscribe. >>>>> To unsubscribe from this group and all its topics, send an email to >>>>> beagleboard...@googlegroups.com. >>>>> To view this discussion on the web visit https://groups.google.co >>>>> m/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. >>>>> >>>> >>>> >>>> -- >>>> Rathin A. Dholakia >>>> "Dont GO through life, GROW through life" >>>> >>>> >>>> -- >>>> 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...@googlegroups.com. >>>> To view this discussion on the web visit https://groups.google.co >>>> m/d/msgid/beagleboard/CAJW6HtQV0Q0hEP9hy8%2BO%3DACnNU1pvjZOr >>>> Lnt_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. >>>> >>>> >>>> >>>> -- >>>> 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/to >>>> pic/beagleboard/ZufgBytqkOI/unsubscribe. >>>> To unsubscribe from this group and all its topics, send an email to >>>> beagleboard...@googlegroups.com. >>>> To view this discussion on the web visit https://groups.google.com/d/ms >>>> gid/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. >>>> >>> >>> >>> >>> -- >>> Rathin A. Dholakia >>> "Dont GO through life, GROW through life" >>> >>> -- >>> 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...@googlegroups.com. >>> To view this discussion on the web visit https://groups.google.com/d/ms >>> gid/beagleboard/CAJW6HtRkpx5AFTVS4TO%2BRxMExenSKSpHMHTPWCLyd >>> wXpZqFyAQ%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. >>> >>> >>> >>> -- >>> 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/to >>> pic/beagleboard/ZufgBytqkOI/unsubscribe. >>> To unsubscribe from this group and all its topics, send an email to >>> beagleboard...@googlegroups.com. >>> To view this discussion on the web visit https://groups.google.com/d/ms >>> gid/beagleboard/2D2AC357-6D81-4E0A-8557-B77092C75B96%40gmail.com >>> <https://groups.google.com/d/msgid/beagleboard/2D2AC357-6D81-4E0A-8557-B77092C75B96%40gmail.com?utm_medium=email&utm_source=footer> >>> . >>> >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> >> >> -- >> Rathin A. Dholakia >> "Dont GO through life, GROW through life" >> >> -- >> 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...@googlegroups.com. >> To view this discussion on the web visit https://groups.google.com/d/ms >> gid/beagleboard/CAJW6HtSHnv4-be-BL%2BiLfVqxiBhFGSKF- >> LHfpWMenr-pRHvw2Q%40mail.gmail.com >> <https://groups.google.com/d/msgid/beagleboard/CAJW6HtSHnv4-be-BL%2BiLfVqxiBhFGSKF-LHfpWMenr-pRHvw2Q%40mail.gmail.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 beagleboard+unsubscr...@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/ > msgid/beagleboard/44723400-4dd4-4911-a7bb-09bb8e96d0ee%40googlegroups.com > <https://groups.google.com/d/msgid/beagleboard/44723400-4dd4-4911-a7bb-09bb8e96d0ee%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 a topic in the > Google Groups "BeagleBoard" group. > To unsubscribe from this topic, visit 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. > To view this discussion on the web visit https://groups.google.com/d/ > msgid/beagleboard/52D25377-CCE3-4257-8665-2F9285EC8FDF%40gmail.com > <https://groups.google.com/d/msgid/beagleboard/52D25377-CCE3-4257-8665-2F9285EC8FDF%40gmail.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- Rathin A. Dholakia "Dont GO through life, GROW through life" -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CAJW6HtTGti_VSzHVaPC6yUBwP0U1YzUz12Hhb-2mLi1PR%3DWp0g%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
