Re: Re. installation of EPICS for beam position measurement using Raspberrypi

[Henrique Almeida <hdante.lnls@gmail.com>]

Em 10/02/2016 14:05, "vivek singh" <viveksingh74155@gmail.com> escreveu:
>
> Hello,
>
> I want to use EPICS in my raspberry pi for beam position measurement.  I will be using 4 16-bit ADC's for digitizing the output of the pickup electrodes. The ADC's support serial and parallel interfaces.  Since the Pi does not have that many GPIOs, I will be using Serial Interface to get the data.  I have a few questions regarding that.
>
> 1. The ADC (AD7622) supports 2MSPS.  I wrote a python code to toggle a GPIO pin on a loop after some calculations and the maximum switching frequency I could observe in the
>     Oscilloscope was 500kHz.  Is that the maximum speed I can achieve using PI ?

If you need to acquire at 2 MSPS without skipping data, the Raspberry PI GPIO is unsuitable for that, since you won't be able to reliably acquire due to the OS and the hardware interrupts. I'm assuming however that you don't need all the data. In this case it doesn't really matter what's the maximum speed, you'll have up to 10~100 ms of "blind" moments, when you don't acquire any data while your application is preempted.

If you need any kind of number, a GPIO read reaches 10 MHz. See, for example:

https://www.raspberrypi.org/forums/viewtopic.php?f=44&t=26907

>
> 2. The Pi has a dedicated SPI interface, so what is the maximum speed that can be achieved using it ?

It may reach 32 Mbps. See:

http://elinux.org/RPi_SPI

>
> Another query I had, was regarding multicore processing capability of the Pi.  
>
> 3. Is it possible to control individual cores, so that they can each perform one task that I assign to them, at their maximum capacity ?

If you're running standard linux, then your tasks will always share and be interrupted by other parts of the OS. You can still move each task to a different core by setting the process affinity or using cpusets. See:

http://man7.org/linux/man-pages/man7/cpuset.7.html

>
>
> Any other suggestions you have regarding this setup would be very

You should be doing this on a microcontroller without an OS that is able to stream the data to a PC, or a storage device. The Raspberry PI is not appropriate.

>
> Thank You,
>
>