The buffer is available here:
/dev/iio:device0
Because the driver uses interrupts, you won’t get the speed you want. The
driver has to be updated to use DMA if you want to use full speed. Reading from
the buffer will reduce your CPU load compared to using LDR_PATH because this
interface blocks until a sample is available, but not long enough for the
thread to sleep. To use DMA, IIO have introduced a DMA framework and most of
what you need is already available. However, IIO are going to be updating the
IIO DMA framework to do zero copy between the kernel module and the socket
interface, using MMU maps.
Regards,
John
> On Mar 18, 2016, at 11:21 AM, Audrey <a...@smith.edu> wrote:
>
> Hi everyone,
>
> First of all, thank you everyone for trying to help me. I appreciate
> everyone's input.
>
> I took everyone's advice, and have moved away from bash to C++. It's clocking
> at about 2 milliseconds, but I would really like it to go down into the
> microsecond range:
> /** Simple LDR Reading Application
> * Written by Derek Molloy for the book "Exploring BeagleBone: Tools and
> * Techniques for Building with Embedded Linux" by John Wiley & Sons, 2014
> * ISBN 9781118935125. Please see the file README.md in the repository root
> * directory for copyright and GNU GPLv3 license information. */
>
> #include<iostream>
> #include<fstream>
> #include<string>
> #include<sstream>
> using namespace std;
>
> #define LDR_PATH "/sys/bus/iio/devices/iio:device0/in_voltage"
>
> int readAnalog(int number)
> {
> stringstream ss;
> ss << LDR_PATH << number << "_raw";
> fstream fs;
> fs.open(ss.str().c_str(), fstream::in);
> fs >> number;
> fs.close();
> return number;
> }
>
> int main(int argc, char* argv[])
> {
> cout << "Starting the readLDR program" << endl;
> int value;
> int i=1;
> while (true)
> {
> float value = (float)readAnalog(0)/4095*1.8;
> cout <<"V= " << value << endl;
> cout << i << endl;
> i++;
> }
> return 0;
> }
>
> Thank you TJF for pointing me to libpruio. I'll use it later if I need it,
> but for now I rather not use the PRU if I don't need to.
>
> So I noticed this thing where I can't see the buffer, or scan_elements, or
> mode in iio:device0, and I wonder if I'm not enabling the adc dto properly or
> something:
> root@beaglebone:/sys/bus/iio/devices/iio:device0# ls -l
> total 0
> -r--r--r-- 1 root root 4096 Mar 1 20:51 dev
> -rw-r--r-- 1 root root 4096 Mar 1 22:03 in_voltage0_raw
> -rw-r--r-- 1 root root 4096 Mar 1 22:03 in_voltage1_raw
> -rw-r--r-- 1 root root 4096 Mar 1 22:03 in_voltage2_raw
> -rw-r--r-- 1 root root 4096 Mar 1 22:03 in_voltage3_raw
> -rw-r--r-- 1 root root 4096 Mar 1 22:03 in_voltage4_raw
> -rw-r--r-- 1 root root 4096 Mar 1 22:03 in_voltage5_raw
> -rw-r--r-- 1 root root 4096 Mar 1 22:03 in_voltage6_raw
> -rw-r--r-- 1 root root 4096 Mar 1 22:03 in_voltage7_raw
> -r--r--r-- 1 root root 4096 Mar 1 20:51 name
> drwxr-xr-x 2 root root 0 Mar 1 20:51 power
> lrwxrwxrwx 1 root root 0 Mar 1 20:50 subsystem -> ../../../../../bus/iio
> -rw-r--r-- 1 root root 4096 Mar 1 20:50 uevent
>
> This is what I've been doing to "enable" the adc (although I don't really
> know what it is doing. I can't find the file cape-bone-iio in bbb, and if I
> try echo cape-bone-iio > test.txt, it is just a regular string.):
> echo cape-bone-iio > /sys/devices/bone_capemgr.*/slots
>
> I tried searching for /driver/iio/adc/ti_am335x_adc.c, but I can't find it
> (there's nothing in root@beaglebone:/sys/bus/iio/drivers#). Could you perhaps
> specify the full filepath?
>
> Thanks.
>
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> <http://beagleboard.org/discuss>
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