Oh, and one more thing; the IIO driver uses a top half and bottom half for handling interrupts, so you won’t see and added latency. All the real work is done in a workqueue.
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 > <mailto: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 >> <mailto: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 >> <mailto: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 >> <mailto: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 >>> <mailto: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 >>> <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>. >>> 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 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>. >> 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 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>. >> 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 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>. > 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 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>. > 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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