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

[Eric Norum <eric@norum.ca>]

I never considered that the original poster was referring to photon BPMs which have signals already in the range acceptable by a 2 MSPS ADC.  If so, please ignore my comments.

The documentation I’ve seen indicates that the SPI rate can be pretty fast:

The SPI can be run at the core clock speed or divided down for slower peripherals. The core clock is 250 MHz. The divider can be set to any power of two - from 2^0 all the way up to 2^16. This means that SPI frequencies from 3.8 kHz to 250 MHz are supported.

The driver supports DMA so you should be able to use a high-speed SPI and get data into the Pi pretty easily.

What analog signal conditioning are you using to get the pickup electrode signals converted to the range that could be measured with a 2 Msample/second ADC?  Typical modern BPMs use ADCs with sampling frequencies in the 100 Msample/second and up range and an FPGA to perform the signal processing and beam position computation.

On Feb 9, 2016, at 9:47 PM, vivek singh <viveksingh74155@gmail.com> wrote:

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 ?

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

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 ?

Any other suggestions you have regarding this setup would be very helpful.

-- 
Eric Norum
eric@norum.ca