1

Has anyone ever tried using raspberry pi as a digital input/output card for high frequency (more than 100 MHz) digital signal? I am thinking about building a CAMAC controller, the interface to PC (I got inspired by this). We used to have old m68k VME computer, which was connected to the dummy controller. As far as I could understand from the circuit board, data cables were almost directly wired to the processor. I think modern processor should manage decoding and interpreting the digital signal almost in real time, so there would be only hardware limitation in things that stand between the cable and the processor. Also, CAMAC uses a huge number of pins: I could see some GPIO extension cards, but I have read elsewhere that GPIO is slow...

So any idea? I would be grateful for it.

  • your link to CAMAC is broken. What is CAMAC?? And yea.. the Pi GPIO has a hard limit of 19.2Mhz due to the clock it runs from. The rate of which the PWN can operate at is NOT dictated by CPU speed, but by the speed of the dedicated clock on the DAC. You talking about 100Mhz here.. that is like oscilloscope territory and require better clocks and digital hardware .. which cost allot more money. – Piotr Kula Nov 15 '16 at 23:34
  • Wow. I see where you going with this :) but if you can get working it would great. I doubt it though :) – Piotr Kula Nov 16 '16 at 11:03
1

The core of the Pi is in effect a mobile phone chip.

Using hardware you might be able to read/write one or two gpios at those frequencies (I'm thinking of the PWM and PCM peripherals).

In practice control of the gpios is in the several microsecond range.

  • I thought the Pi could only generate up to few hundred kilohertz on the GPIO... .And what, Pi is a mobile phone chip? In what way.. it has not GSM on it.. You lost me there :D – Piotr Kula Nov 15 '16 at 23:26
  • Apparently max at 19.2Mhz? ... given the OS doesnt throttle it. – Piotr Kula Nov 15 '16 at 23:28
  • codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed Apprently he got 22Mhz with some native C code. Am I missing something? How would the OP generate 100Mhz? – Piotr Kula Nov 15 '16 at 23:32
  • You can drive the PWM or PCM peripherals from a number of clock sources. My pigpio uses a 500 MHz clock which allows for the generation of a 250MHz signal. There is a 1000MHz clock which could be used. A divider of 10 would give a 100MHz signal (Pi clock dividers are even with a minimum value of 2). In practice I understand the problem is in adding wires to the GPIO such that those high frequency signals still exist on the wire. I don't know the highest actually achieved. – joan Nov 16 '16 at 9:00
  • Cool. That is very interesting. Can the GPIO read 100mhz if testing another Pi generating 100mhz ? Basic osciscope I guess? – Piotr Kula Nov 16 '16 at 11:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.