Hi John, Thanks a lot for this very complete answer ! I think I understand it now, the last point I am not sure about is:
ti,chan-step-avg = <1 1 1 1 1 1 1 1> /* 2 sample average */ I went through 12.3.3 of the AM3358 Technical Reference Manual and it seems that the setting the averaging value to 1 disable the averaging (instead of setting it to 2) am I right? Thanks again for your help Le mercredi 11 avril 2018 17:00:54 UTC-4, john3909 a écrit : > > > > On Apr 11, 2018, at 6:04 AM, pierric...@gadz.org <javascript:> wrote: > > Hi John, > Thanks for the help, I looked into the iio_generic_buffer.c example and i > patched it to disable the hardware triggers thanks to the patch presented > on this page : https://www.teachmemicro.com/beaglebone-black-adc/ I am > now able to reader a buffer from the different channel. > However I have 2 majors questions that remains: > > 1) I only want to use on channel, then I do not want the ADC to sample the > other one so that i'll have the maximum sampling rate. What is the best way > to disable the channel? If I do not enable them in iio_generic_buffer.c I > am not sure that the ADC is not going to sample this channel or not (well, > I think it wont sample but I prefer to be sure). Is it preferable to not > mention them on the devicetree so that Linux wont know that there are > multiple channels on the ADC? This part is not very clear for me. > > 2) To change the sample frequency of the ADC you mentioned that it is done > using the device tree however I did not find any argument on the ADC > devicetree to change the sampling frequency. I read the discussion you had > on this post (https://patchwork.kernel.org/patch/9391487/ ) but it is not > clear if the frequency setting is done using the kernel module or > devicetrees. Could you explain me this please? > > Looking at this a little more, there is a mistake in the ADC DT file > BB-ADC-0A00.dts. The maximum averaging is 16, not 0x16. > > The line > ti,chan-step-avg = <0x16 0x16 0x16 0x16 0x16 0x16 0x16 0x16> > > should be changed to > ti,chan-step-avg = <16 16 16 16 16 16 16 16> > Fortunately, the driver does a range check and sets the value to 16. > > ti,chan-step-avg = <1 1 1 1 1 1 1 1> /* 2 sample average */ > ti,chan-step-opendelay = <0 0 0 0 0 0 0 0> > ti,chan-step-sampledelay = <0 0 0 0 0 0 0 0> > > To achieve a conversion rate of 800 KS/s > > From ti_am335x_tscad.c, 1 + (1 + 13) * 2 = 30 cycles > > The ADC uses a 24 MHz clock, so 1/24,000,000 * 15 = 800 KS/s > > You could increase the sampling rate to 1.6MS/s by changing the average to > 0, which means there is no averaging. To achieve this, the minimum number > of cycles for a conversion is 15 (12.3.7 of the AM3358 Technical Reference > Manual) > > 1 + (1 + 13) * 1 = 15 cycles > > which will give you 1.6 MS/s > > Regards, > John > > > Thanks a lot > > Pierrick > > Le mercredi 28 mars 2018 00:45:01 UTC-4, john3909 a écrit : >> >> Look at the kernel source under tools/iio for examples on how to use IIO. >> >> Regards, >> John >> >> >> >> >> >> On Mar 27, 2018, at 12:10 PM, pierric...@gadz.org wrote: >> >> Hi John, >> >> Sorry for the late answer, I had hard time using the PRUs and I am now >> going to use the IIO ADC driver, I am able to read the sample with the cat >> command in /sys/bus/iio/devices/iio:device0/in_voltage3_raw >> However I am not able to use Libiio in order to read data from a user >> space application, I am reading (nil) instead of my data. Do you have any >> idea of where does the problem comes from ? >> >> Here is the code I am using in the user space : >> >> >> #define _BSD_SOURCE >> #define _GNU_SOURCE >> #define _DEFAULT_SOURCE >> >> #include <cdk/cdk.h> >> #include <locale.h> >> #include <pthread.h> >> #include <stdbool.h> >> #include <unistd.h> >> #include <stdint.h> >> #include <stdio.h> >> #include <string.h> >> >> #ifdef __APPLE__ >> #include <iio/iio.h> >> #else >> #include <iio.h> >> #endif >> >> struct iio_context *ctx; >> struct iio_device *dev; >> struct iio_channel *ch; >> >> int main() >> { >> ctx = iio_create_default_context(); >> dev = iio_context_get_device(ctx, 0); >> ch = iio_device_get_channel(dev, 3); >> >> >> iio_device_attr_write_longlong(dev, "sample_rate", 100); >> iio_channel_attr_write_double(ch, "scale", 1); >> >> iio_channel_enable(ch); >> >> char *a = iio_device_get_data(dev); >> printf("%p\n", a); >> >> iio_channel_disable(ch); >> >> return 0; >> } >> >> Thanks >> >> Pierrick >> >> >> Le lundi 26 février 2018 16:46:11 UTC-5, john3909 a écrit : >>> >>> The IIO ADC driver can run at 800K samples per second. Here is the patch >>> that made that possible. >>> >>> https://patchwork.kernel.org/patch/9391487/ >>> >>> I can confirm that I have tested the driver at 800Ksps and it works fine >>> as long as you have a proper low impedance source for each ADC channel. CPU >>> utilization was about 5% if I recall and that was probably used by the iiod >>> daemon, which I used to display the waveform on a remote Linux app. >>> >>> There is example code in the original Starterware for McSPI, which >>> should work fine if you are using the PRU low level drivers. >>> >>> Regards, >>> John >>> >>> >>> >>> >>> On Feb 26, 2018, at 12:56 PM, pierric...@gadz.org wrote: >>> >>> Thanks John, >>> >>> I am now working with the starterware_PRU but i did not find examples >>> for using the McSPI with the PRU, do you think it will be hard to adapt the >>> initial code to the PRU ? >>> By the way, looking to the IIO driver documentation, it seems that for >>> the AM335x chip the max sampling rate is only 200k samples per second which >>> may not be enough : >>> http://processors.wiki.ti.com/index.php/Linux_Core_ADC_Users_Guide ; am >>> I right ? >>> >>> >>> Thanks >>> >>> Pierrick >>> >>> Le lundi 19 février 2018 23:15:50 UTC-5, john3909 a écrit : >>>> >>>> Like I said, it was based on Starterware, so search Github for >>>> starterware and you will see a project starterware_PRU. It does use the >>>> mcspi, so it is not a bitbang implementation. >>>> >>>> Regards, >>>> John >>>> >>>> >>>> >>>> >>>> On Feb 19, 2018, at 7:33 PM, pierric...@gadz.org wrote: >>>> >>>> Thanks John for you answer, I was quit busy last week so I worked on >>>> this during the Weekend. >>>> >>>> Unfortunately, I was not able to find a project that is using the SPI >>>> and I2C interface with the PRU, I only found this one : >>>> >>>> https://github.com/chanakya-vc/PRU-I2C_SPI_master/wiki/SPI-Master-Controller >>>> >>>> But it is using bit banging for the SPI part and not using the on-board >>>> pull-up resistors for the I2C part. >>>> >>>> Concerning the ADC, I'll have a loook at the UIIO drivers in the coming >>>> days it seems that it meets my need in term of real-time acquisition. >>>> >>>> Regards, >>>> >>>> Pierrick >>>> >>>> -- >>>> 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/msgid/beagleboard/74949832-b67c-430f-811e-f3b2fff83852%40googlegroups.com >>>> >>>> <https://groups.google.com/d/msgid/beagleboard/74949832-b67c-430f-811e-f3b2fff83852%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 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/msgid/beagleboard/3dc611e5-04e7-45bb-87d4-3c21a5665cec%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/beagleboard/3dc611e5-04e7-45bb-87d4-3c21a5665cec%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 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/msgid/beagleboard/18b69929-99ca-4e7e-8539-df962a17941d%40googlegroups.com >> >> <https://groups.google.com/d/msgid/beagleboard/18b69929-99ca-4e7e-8539-df962a17941d%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 the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to beagleboard...@googlegroups.com <javascript:>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/940610ad-a88c-4918-a3e2-15d7c88d77d1%40googlegroups.com > > <https://groups.google.com/d/msgid/beagleboard/940610ad-a88c-4918-a3e2-15d7c88d77d1%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 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/ef59523c-02ab-4c58-992a-2b37c0744ff0%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
