And thats the problem. It's not consistent, and nothing is of this sort. On Thu, Mar 3, 2016 at 12:35 AM, John Syne <john3...@gmail.com> wrote:
> Well, it does, but not consistently, hence the interrupt latency issue. > For the most part, linux can respond to interrupts in the uS range, > especially when the CPU load is low. When the CPU load is high, the latency > does get worse. However, UIO event handling is about a 1,000 slower than > interrupts in kernel code. > > Regards, > John > > > > > On Mar 2, 2016, at 11:27 PM, William Hermans <yyrk...@gmail.com> wrote: > > *Wrong again, UIO attempts to handle interrupts as events, but the concept >> is slow (typically ms, not us)* >> > > You're full of it if you're trying to purport that any interrupt in Linux > works in the uS range. > > On Thu, Mar 3, 2016 at 12:26 AM, John Syne <john3...@gmail.com> wrote: > >> Wrong again, UIO attempts to handle interrupts as events, but the concept >> is slow (typically ms, not us) >> >> Regards, >> John >> >> >> >> >> On Mar 2, 2016, at 11:22 PM, William Hermans <yyrk...@gmail.com> wrote: >> >> *mmap isn't faster than a kernel driver (kernel code has priority over >>> user space code) and you still cannot handle interrupts from user space. >>> Anyway, you won’t find any drivers in the kernel implemented your way >>> (/dev/mem, mmap). However, mmap is used in drivers to eliminate mem to mem >>> copy when transferring data between user space and kernel space. * >>> *Regards,* >>> >> *John* >> >> Now. not only are you wrong, but you're making stuff up. You can handle >> interrupts from userspace, as much as iio can. But it's not my job to tell >> you how. I will mention that perhaps you should look into "userspace >> drivers". As far as whats faster ? who f***ing cares. mmap() is a lot >> faster than the ADCs . . . and still not the point. >> >> The point is, if you need fast ADC you should be using the PRU, and then >> you may want to seriously consider using an external module. That is, for >> anything serious. It does not matter how much CPU mmap() or iio uses. As >> any % can preempt other code that needs to run *now* thus creating >> potential non determinism. >> >> >> On Thu, Mar 3, 2016 at 12:12 AM, John Syne <john3...@gmail.com> wrote: >> >>> mmap isn't faster than a kernel driver (kernel code has priority over >>> user space code) and you still cannot handle interrupts from user space. >>> Anyway, you won’t find any drivers in the kernel implemented your way >>> (/dev/mem, mmap). However, mmap is used in drivers to eliminate mem to mem >>> copy when transferring data between user space and kernel space. >>> >>> Regards, >>> John >>> >>> >>> >>> >>> On Mar 2, 2016, at 11:04 PM, William Hermans <yyrk...@gmail.com> wrote: >>> >>> *From what I remember, the solution you proposed was using 90% of the >>>> CPU. * >>>> >>> >>> 93% CPU load when using one shot mode, and continuously opening / >>> closing a file descriptor to the ADC module. There is no such load when >>> using mmap(), as mmap() is light years faster. >>> >>> >>> On Wed, Mar 2, 2016 at 11:52 PM, John Syne <john3...@gmail.com> wrote: >>> >>>> When the ADC is in continuous mode, you shouldn't read the data until >>>> it has been updated. Simply reading the data over and over again to get the >>>> same value that hasn’t been updated is just dumb. The interrupt tells you >>>> when the conversion has been updated and then you read it. The point I was >>>> making originally was that there was no need to use PRU to sample the ADC >>>> at full speed. You can do the same from the IIO driver. Running at full >>>> speed consumes less than 10% of the CPU. If the IIO driver was updated to >>>> use DMA, then there would be no CPU utilization. From what I remember, the >>>> solution you proposed was using 90% of the CPU. >>>> >>>> Regards, >>>> John >>>> >>>> >>>> >>>> >>>> On Mar 2, 2016, at 10:12 PM, William Hermans <yyrk...@gmail.com> wrote: >>>> >>>> *First, that isn’t going to work because the ADC uses a scan loop and >>>>> unless you can respond to interrupts, you cannot determine when the ADC >>>>> conversion has completed. There is a much simpler way to do this. Simply >>>>> use the IIO driver and then* >>>>> >>>> >>>> FIrst of all, it *will* work. I've done it, and it works. Second of >>>> all, in continuous mode, values are put out as 32bit values. Only the first >>>> 12bits is the actual ADC value. The next 4 bits is the channel ID( 0 - 7 ), >>>> and the last 16bits reserved / unused. Thirdly, using interrupts in fast >>>> moving code is about as bad of an idea as using try / catch blocks in fast >>>> moving code. It adds code latency, and also introduces non deterministic >>>> behavior. This is why iio does not work fast for short data sets. >>>> >>>> >>>> *dd if=/dev/iio:device0 of=~/test* >>>>> >>>> >>>> Maybe, but it's a terrible idea if the target is flash media. The ADC's >>>> can, and will use up a lot of storage space, very quickly. Just using 7 >>>> channel in one shot mode, one channel after the next. In a loop of 300k >>>> iterations. I was using up ~3MB/s disk space. Maxed out, and all channel >>>> used. The ADC's should use up ~9MB/s or more. >>>> >>>> >>>> On Wed, Mar 2, 2016 at 4:06 PM, John Syne <john3...@gmail.com> wrote: >>>> >>>>> First, that isn’t going to work because the ADC uses a scan loop and >>>>> unless you can respond to interrupts, you cannot determine when the ADC >>>>> conversion has completed. There is a much simpler way to do this. Simply >>>>> use the IIO driver and then read /dev/iio:device0 >>>>> >>>>> For example, do: >>>>> >>>>> dd if=/dev/iio:device0 of=~/test >>>>> >>>>> Enable the iio buffer and your file will receive samples at the >>>>> configured speed. >>>>> >>>>> Regards, >>>>> John >>>>> >>>>> >>>>> >>>>> >>>>> On Mar 2, 2016, at 2:27 PM, William Hermans <yyrk...@gmail.com> wrote: >>>>> >>>>> errr oops, I sent too soon. mmap() is fast, and can actually read from >>>>> the ADC faster than the ADC can update values. But, it's using the main >>>>> processor to do so, and if you need to do more than just read the ADC. >>>>> Additional processes would have to compete for processor time. So, if one >>>>> does want / need to read at maximum speed, it might be wise to offload the >>>>> main processor, by using a PRU. >>>>> >>>>> It would not matter if this were done in userspace, or kernel space. >>>>> It'll definitely put a load strain on the ARM processor. >>>>> >>>>> On Wed, Mar 2, 2016 at 3:19 PM, William Hermans <yyrk...@gmail.com> >>>>> wrote: >>>>> >>>>>> *You realize that you can read the ADC from Linux at full speed also? >>>>>>> No need to use the PRU. * >>>>>>> *Regards,* >>>>>>> >>>>>> *John* >>>>>> >>>>>> I do, because I've proven just that :) *mmap()* is dahmed fast . . . >>>>>> >>>>>> >>>>>> On Wed, Mar 2, 2016 at 2:32 PM, John Syne <john3...@gmail.com> wrote: >>>>>> >>>>>>> You realize that you can read the ADC from Linux at full speed also? >>>>>>> No need to use the PRU. >>>>>>> >>>>>>> Regards, >>>>>>> John >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Mar 2, 2016, at 12:43 PM, TJF <jeli.freih...@gmail.com> wrote: >>>>>>> >>>>>>> Hello PatM001! >>>>>>> >>>>>>> There's libpruio <http://beagleboard.org/project/libpruio/>, which >>>>>>> provides ADC sampling at full speed (200 kHz). You'll get rid of the >>>>>>> exeptions (and the miss readings of the sysfs driver in case of sampling >>>>>>> multiple channels). >>>>>>> >>>>>>> The downside: no C# binding yet. It's written in FreeBASIC/PASM and >>>>>>> gets shipped with a C header. You may try SWIG >>>>>>> <http://www.swig.org/> on the C header in order to generate a >>>>>>> binding for your prefered language. >>>>>>> >>>>>>> If you try, please share your results, or at least report. >>>>>>> >>>>>>> BR >>>>>>> >>>>>>> -- >>>>>>> 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. >>>>>>> >>>>>> >>>>>> >>>>> >>>>> -- >>>>> 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. >>>>> >>>> >>>> >>>> -- >>>> 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. >>>> >>> >>> >>> -- >>> 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 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