Feb 18, 2021, 23:44 by [email protected]: > Realtime isn't about latency but determinism and the standard usb driver > stack is non-deterministic. I believe there are realtime capable stacks for > usb devices but it needs to be supported by both devices. And I don't think > most mcus support it. > Latency is an integral part of determinism. The larger the uncertain latency part will be, the bigger the limit until when the information is valid will need to be. And real-time in how Machinekit-HAL understands it and uses it is all about the top maximum when the information has to be processed, not the minimum or absolute gradual, sequential time of each step. (You can look at how the HAL modules, both drivers and components, are conceptually programmed and compiled, there are no time constant execution path, the same amount of jumps or other similar real-time concepts.)
Pretty much all it cares about is to start the linked list of functions comprising the HAL thread at a given monotonic clock tick. > > If you don't care about the smoothness of tour motion or use a buffered > approach, usb works fine. > Yes, buffered approach is one way to use USB. It really depends on for what you want to use it, if your application can live with the latency of - let's say - 5 ms, because your monotonic clock is ticking at 20 ms, well, then you are going to be fine. Cern. > > On Fri 19. Feb 2021 at 0.36, justin White <> [email protected]> > wrote: > >>> It's not that simple. USB2 has higher latencies, true, but if you are OK >>> with them, then the USB2 interface is as capable of real-time communication >>> as any other interface. There have been attempts to mitigate these >>> latencies with various results. (Search research papers online.) USB3 >>> should be much better in this regard. >>> >> >> I dont see how that's true when the default USB2 polling rate is 8ms. You >> can change the mouse driver to get 1ms but I don't know that the RT patches >> touch USB. So whats the secret sauce to getting RT USB if the polling >> interval remains at 8ms on a shared bus? >> >> USB3 isn't really even worth talking about yes its peer to peer with much >> better latency but an rpi4 having a USB3 port doesn't do any good when MCUs >> really do not. Most MCUs bake usb2 hardware right onto the chip while usb3 >> is generally a PCIE lane attached to a PHY which I have yet to see on any >> dev boards. >> >> So what's the secret sauce to RT USBx? And .......why, when any MCU contains >> fast UARTs, spi and sometimes ethernet. >> >> On Thu, Feb 18, 2021 at 11:23 AM cern via Machinekit <>> >> [email protected]>> > wrote: >> >>> Hello, >>> >>> Feb 18, 2021, 14:32 by >>> [email protected]>>> : >>> >>> > USB itself isn’t realtime capable so it can’t be used for any realtime >>> tasks. >>> > >>> It's not that simple. USB2 has higher latencies, true, but if you are OK >>> with them, then the USB2 interface is as capable of real-time communication >>> as any other interface. There have been attempts to mitigate these >>> latencies with various results. (Search research papers online.) USB3 >>> should be much better in this regard. >>> >>> Cern. >>> >>> > >>> > On Thu 18. Feb 2021 at 11.18, > >>> [email protected]>>> > <> >>> >>> [email protected]>>> > > wrote: >>> > >>> >> Be interesting to see more details on the Linuxcnc\USB\MESA setup. >>> >> As far as I was aware there was no RT support for USB. >>> >> I'm not even sure if MESA themselves recommend their USB boards for use >>> with Linuxcnc. >>> >> >>> >> On Thursday, February 18, 2021 at 7:32:57 AM UTC+11 >> >>> >>> [email protected]>>> >> wrote: >>> >> >>> >>> Great, thanks for finding it! >>> >>> >>> >>> I've seen lots of people purchasing 3DP controller boards to upgrade >>> 3DP/Lasers/CNC's(consumer stuff) and many of them also use an rPi with >>> OctoPrint or CNCjs, GridBot etc. >>> >>> I like this approach in that all of my macines(4 3DPs, 2 laser cutters >>> and 1 CNC) all have consumer grade controllers in them running on different >>> uCPUs. Some AVR328, STM32, LPC17xx and one a BBB/CRAMPS. >>> >>> But would love to be able to have LinuxCNC/Machinekit on an rPi doing >>> the control, UI, setup. >>> >>> On Wednesday, February 17, 2021 at 11:02:18 AM UTC-8 >>> >>> >>> [email protected]>>> <>>>> wrote: >>> >>> >>> >>>> Hi, >>> >>>> the code is available in >>>> >>> >>> https://github.com/scottalford75/Remora>>> >>>> - looks like he though >>> that spiPRU is not a great name and changed it to something more flashy. >>> >>>> >>> >>>> Looks interesting from programming point of view, but I wonder how >>> many people would buy Smoothieboard and RPi both to run 3D printer with >>> LinuxCNC on it? Most will stay with Smoothie, I think. >>> >>>> >>> >>>> Cern. >>> >>>> >>> >>>> Dne úterý 16. února 2021 v 19:18:20 UTC+1 uživatel >>>> >>> >>> [email protected]>>> <>>>>> napsal: >>> >>>> >>> >>>>> I was about to start on setting up a Xylotex BareBoneCNC with a >>> BBB/Machinekit and thought I'd look at what's going on with Raspberry Pi in >>> CNC world. I found a video of a guy driving a Mesa board over USB with >>> LinuxCNC and it looked impressive(doesn't take much). >>> >>>>> >>> >>>>> Got to wondering if a standard 3DP controller like SKR, >>> Smoothieboard, etc couldn't run firmware similar to the MESA board and only >>> found mention of this spiPRU but no details, code, anything. >>> >>>>> >>> >>>>> >>> https://github.com/scottalford75/LinuxCNC-on-RPi >>> >>>>> >>> >>>>> I searched for spiPRU here and in general inter-web lands and found >>> nothing but the mention of it in the above git repo. If anyone knew about >>> it I figured they would be here. >>> >>>>> Thx >>> >>>>> >>> >> >>> >> >>> >> >>> >> -- >>> >> website: >> >>> http://www.machinekit.io>>> >> blog: >> >>> >>> http://blog.machinekit.io>>> >> github: >> >>> >>> https://github.com/machinekit >>> >> --- >>> >> You received this message because you are subscribed to the Google >>> Groups "Machinekit" group. >>> >> To unsubscribe from this group and stop receiving emails from it, send >>> an email to >> >>> [email protected] >>> <mailto:machinekit%[email protected]>>>> >> . >>> >> To view this discussion on the web visit >> >>> >>> https://groups.google.com/d/msgid/machinekit/cc241b97-47bb-48d0-b3b4-e595dc809b55n%40googlegroups.com>>> >>> <>>> >>> https://groups.google.com/d/msgid/machinekit/cc241b97-47bb-48d0-b3b4-e595dc809b55n%40googlegroups.com?utm_medium=email&utm_source=footer>>> >>> >>> . >>> >> >>> > -- >>> > Terv, >>> > Joonas Forsell >>> > >>> > >>> > >>> > -- >>> > website: > >>> http://www.machinekit.io>>> > blog: > >>> >>> http://blog.machinekit.io>>> > github: > >>> https://github.com/machinekit >>> > --- >>> > You received this message because you are subscribed to the Google >>> Groups "Machinekit" group. >>> > To unsubscribe from this group and stop receiving emails from it, send >>> an email to > >>> [email protected] >>> <mailto:machinekit%[email protected]>>>> > . >>> > To view this discussion on the web visit > >>> >>> https://groups.google.com/d/msgid/machinekit/CA%2B%2BSnhq%3D-rmGD2z8ewbQ9ryBoyWgwymJTbmWp6NKnGPyhmsrbw%40mail.gmail.com>>> >>> <>>> >>> https://groups.google.com/d/msgid/machinekit/CA%2B%2BSnhq%3D-rmGD2z8ewbQ9ryBoyWgwymJTbmWp6NKnGPyhmsrbw%40mail.gmail.com?utm_medium=email&utm_source=footer>>> >>> >> . >>> > >>> >>> >>> >>> -- >>> website: >>> http://www.machinekit.io>>> blog: >>> >>> http://blog.machinekit.io>>> github: >>> https://github.com/machinekit >>> --- >>> You received this message because you are subscribed to the Google Groups >>> "Machinekit" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to >>> [email protected] >>> <mailto:machinekit%[email protected]>>>> . >>> To view this discussion on the web visit >>> >>> https://groups.google.com/d/msgid/machinekit/MTpwssk--3-2%40tuta.io>>> . >>> > -- > Terv, > Joonas Forsell > > > > -- > website: > http://www.machinekit.io> blog: > http://blog.machinekit.io> > github: > https://github.com/machinekit > --- > You received this message because you are subscribed to the Google Groups > "Machinekit" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to > [email protected]> . > To view this discussion on the web visit > > https://groups.google.com/d/msgid/machinekit/CA%2B%2BSnhrgbwYbXtseCcC6hZmb%3D1-7HcBJSmS2bzHhEs%2BnSuUbpg%40mail.gmail.com > > <https://groups.google.com/d/msgid/machinekit/CA%2B%2BSnhrgbwYbXtseCcC6hZmb%3D1-7HcBJSmS2bzHhEs%2BnSuUbpg%40mail.gmail.com?utm_medium=email&utm_source=footer>> > . > -- website: http://www.machinekit.io blog: http://blog.machinekit.io github: https://github.com/machinekit --- You received this message because you are subscribed to the Google Groups "Machinekit" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/machinekit/MUAtO_U--3-2%40tuta.io.
