20 ms·

This might be of interest: http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/ http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-.

This might be of interest: http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/ http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-...

Aeolos 11y ago
Excellent, thanks! So GPIO performance won't be a problem, but they note that OS multitasking can cause issues: "What is not evident from the snapshots, however, is that due to multitasking nature of Linux, the GPIO manipulation is constantly interrupted for short periods when the CPU is doing something else, such as receiving or sending data over network, writing log files, etc" Running on bare metal should take care of that, so the only remaining problem is how to synchronize the signal generation on the RPi with the recording of data on the host computer. (Sigh, if only RPi had a USB3 port...)
- timow1337 11y ago
  The new raspberry pi zero can be run as a device, so you could use that.
  - Aeolos 11y ago
    O.o this $5 puppy could essentially replace the 1.5K National Instruments DAQ I'm using right now. Even better, I won't have to deal with their horrendous API documentation anymore. Of course that would require a Linux kernel, so not bare metal anymore, but there might be a way to make this work! Now I just need to get my hands on one, it's out of stock everywhere within a radius of 300km...
    - ajb 11y ago
      They haven't committed to making more, or if they do, to the $5 price point.
      - ju-st 11y ago
        Really?? Then the zero was a really shitty marketing move...
      - Narishma 11y ago
        They are making more, but they sell them faster than they can make them.
- brobinson 11y ago
  >due to multitasking nature of Linux, the GPIO manipulation is constantly interrupted for short periods when the CPU is doing something else, such as receiving or sending data over network, writing log files, etc. With a few simple tweaks (isolcpus + irqbalance + setting cpu affinity), you can get rid of the overwhelming majority of interruptions a specific userland program running on a Linux machine could encounter. If this quote is talking about kernel context switches, choice of I/O scheduler and tick rate in the kernel could be tweaked for better performance.
- roywiggins 11y ago
  You could probably use an Arduino for this, they connect to a computer using serial-over-USB. You can do GPIO bit-twiddling pretty fast: http://skpang.co.uk/blog/archives/323 http://skpang.co.uk/blog/archives/323

This might be of interest: http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/ http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-...

Aeolos 11y ago

Excellent, thanks! So GPIO performance won't be a problem, but they note that OS multitasking can cause issues: "What is not evident from the snapshots, however, is that due to multitasking nature of Linux, the GPIO manipulation is constantly interrupted for short periods when the CPU is doing something else, such as receiving or sending data over network, writing log files, etc" Running on bare metal should take care of that, so the only remaining problem is how to synchronize the signal generation on the RPi with the recording of data on the host computer. (Sigh, if only RPi had a USB3 port...)

timow1337 11y ago
The new raspberry pi zero can be run as a device, so you could use that.
- Aeolos 11y ago
  O.o this $5 puppy could essentially replace the 1.5K National Instruments DAQ I'm using right now. Even better, I won't have to deal with their horrendous API documentation anymore. Of course that would require a Linux kernel, so not bare metal anymore, but there might be a way to make this work! Now I just need to get my hands on one, it's out of stock everywhere within a radius of 300km...
  - ajb 11y ago
    They haven't committed to making more, or if they do, to the $5 price point.
    - ju-st 11y ago
      Really?? Then the zero was a really shitty marketing move...
    - Narishma 11y ago
      They are making more, but they sell them faster than they can make them.
brobinson 11y ago
>due to multitasking nature of Linux, the GPIO manipulation is constantly interrupted for short periods when the CPU is doing something else, such as receiving or sending data over network, writing log files, etc. With a few simple tweaks (isolcpus + irqbalance + setting cpu affinity), you can get rid of the overwhelming majority of interruptions a specific userland program running on a Linux machine could encounter. If this quote is talking about kernel context switches, choice of I/O scheduler and tick rate in the kernel could be tweaked for better performance.
roywiggins 11y ago
You could probably use an Arduino for this, they connect to a computer using serial-over-USB. You can do GPIO bit-twiddling pretty fast: http://skpang.co.uk/blog/archives/323 http://skpang.co.uk/blog/archives/323