4 ms·
Linuxcnc on a raspberry pi 4 is fast enough to run the motion-control loop of linuxcnc with 1kHz, worst case latency is below 100us with current rt-preempt kern
by rmu09 7y ago
Linuxcnc on a raspberry pi 4 is fast enough to run the motion-control loop of linuxcnc with 1kHz, worst case latency is below 100us with current rt-preempt kernels.
Generation of stepper signals or interfacing with servo amplifiers and encoders is best left to an external microcontroller of FPGA card, connected either via SPI or ethernet.
- ampdepolymerase 7y agoHow do the audio and video subsystems of standard Linux systems deal with real time requirements?
- mdtusz 7y agoBuffers.
- bsder 7y agoBadly. Only macOS has an architecture to deal with low-latency audio and video properly. Presumably iOS has some of those features as well, but it was on OS X that Apple did some deep architectural changes for proper low-latency audio and video.
- tonyarkles 7y agoIt was admittedly several years ago, but I worked on a voice chat app for iOS and Android, and the behaviour on Android was horrifying. iOS had very consistent and great audio latency (approx 10ms if I recall). Android devices were all over the place; I think the worst one I tested was over 150ms.
- unlinked_dll 7y agoUsing the RT Preempt kernel patch, if you care about latency.
- bsder 7y agoAnd yet the Beaglebone Black has been able to handle this down at the 100-200nS level in the PRUs. For years. While I admire the ingenuity of people doing real-time with Linux, I just shake my head at the man hours wasted that they could be doing the "thing they want to do" instead of fighting Linux.
- rmu09 7y agoAnd the Beaglebone runs what OS? Linux? The PRUs are just the replacement for the FPGA resp. microcontroller. You have your relatively relaxed control loop running at e.g. 1kHz on the main ARM and the tightly constrained stuff on the PRUs, not much difference to running it on something external connected via SPI. Some kind of external hardware is needed anyways, doesn't make much difference including a STM32. The problem with beaglebone is lacking GPU afaik.
- NegativeLatency 7y agoMaybe the thing they want to do IS fighting Linux?