Yes so far as I understand the PRU runs autonomously from the core and they use DMA to transfer data. It is my understanding that there are no interrupts that will influence the PRU's and they run smoothly. The 3D printer guys use it and any delays or interrupts shows up on the quality of the product.
As for the salesman bit, I have no affilaitation with machinekit nor do I work for them :) I do like the TI chip and the BBB platform. My product is based on the CherryBlossom from Arrow. I am also looking at machinekit all the time mainly because I am developing other non cnc products on the same platform and the forum is shared. The machinekit boys really undestand the working of the PRU very well and many people learn from their work. I noticed that one of our friends (ArcEye) has done some work on the display using QT but I dont know how far he got with that. >You work like a sales person, everything is good without promising >anything. Do you know if they handle priorities properly? No uknown >delays for like 100µs every now and then? Clock rate of 200kHz is this >the rate it can execute tasks realiable? > >Display must be solved but if it have Ethernet X11 this might be a very >good option. I already have running on ordinary compture with inverters >made myself although a moment ago then I was away for five minutes I >got an unexpected delay message. The best would probably a protocol to >talk the real time part of linuxcnc via some kind of protocol and in >such design of user interface would be very flexible. > >Nicklas Karlsson > > >On Wed, 03 Feb 2016 13:25:35 +0000 >"Marius Liebenberg" <[email protected]> wrote: > >> Hi Nicklas >> The rpi does not have the same performance as the BBB when it come to >> the IO stuff we are talking about here. The BBB has a TI chip that >>has >> two very fast MCU's build into the core (over and above the actual >>ARM >> core). They handle the IO stuff via some DMA arrangements. The RPI >>does >> not have these MCU's and must do the IO in another fashion. >> Mashinekit is a port of linuxcnc that runs very well on the BBB at >>this >> time. >> The MCU's on the BBB can handle a clock rate of up to 200Khz. I think >> the STM32 will have a hard time to get to that if at all. If I can >>give >> some advise I would say have a look at what is happening with the BBB >> and machinekit. There are FPGA boards running Hostmot driver >>interfaces >> already. And a heap of other developments. >> In conculsion I would say that you should get a better performance >>from >> the BBB than from most Pc's. The display is another story still but >>with >> the introdcution of FPGA stuff, the display issues might be gone soon >>as >> well. >> >> >> ------ Original Message ------ >> From: "Nicklas Karlsson" <[email protected]> >> To: "EMC developers" <[email protected]> >> Sent: 2016-02-03 14:46:26 >> Subject: Re: [Emc-developers] Prempt RT on Raspi/ARM >> >> >Yes I read post, Rapberry and beagle bone are fantastic cards. Is >>there >> >any small unknown delays then running on Raspi or Beagle bone? Or is >> >the problem the same as on an ordinary computer, usually work well >> >enough? >> > >> >I do not expect more from Beagle/Raspberry unless they have been >>able >> >to get proper handling of interrupt priorities since they are less >> >powerful than ordinary computer. Do you know if Beagle/Raspberry >>have >> >proper handling of interrupt priorities in kernel? >> > >> >STM32 I would expect more from because it's known there is nothing >>else >> >disturbing. As is now I am using Preemt RT but for the long run I >>will >> >try get something I know perform as expected every time. >> > >> >A small jerk every now and then is OK for youtube or telephone but >>less >> >so then machining part because it stick to the part. >> > >> > >> >Nicklas Karlsson >> > >> > >> > >> >On Wed, 3 Feb 2016 13:13:07 +0100 >> >"W. Martinjak" <[email protected]> wrote: >> > >> >> Did you read my post/question, or is this a simple reflex answer? >> >> >> >> On 2016-02-03 12:50, Nicklas Karlsson wrote: >> >> > I was thinking more about something like the STM32 discovery >> >>boards. The STM32 micro controller have an Cortex-* CPU with nested >> >>interrupt controller. The Raspi is essentially an ordinary computer >> >>and I have not been able to figure out if it have nested interrupts >> >>and the idea was to get rid of everything that may delay CPU every >>now >> >>and then. I run control loop at 40kHz which is equal to a period of >> >>25µs on STM32 and it works perfect including low priority taks not >> >>because of performance but because nothing will stop it from >>getting >> >>the necessary clock cycles then needed. >> >> > >> >> > GUI --> G-code, motion planner and other real time --> Motor >> >>controlling switches. >> >> > >> >> > GUI would be on ordinary computer which usual work well but may >> >>delay CPU every now and then. >> >> > G-code, motion planner and other real time would be on micro >> >>controller which may not delay CPU every now and then. >> >> > Motor controlling switches would be on separate card, usually >>there >> >>is need for electrical isolation anyway especially if running from >> >>voltage which may be dangerous. >> >> > >> >> > >> >> > The point is to get rid of the annoying delay for unknown >>reason >> >>every now and then. What is good enough for video with maybe 50 >>frame >> >>per second is not good enough for tasks running twenty times as >>often >> >>even if CPU is very fast but small unknown delays may happen. >> >> > >> >> > >> >> > Nicklas Karlsson >> >> > >> >> > >> >> > >> >> > On Wed, 3 Feb 2016 12:23:11 +0100 >> >> > "W. Martinjak" <[email protected]> wrote: >> >> > >> >> >> OK, not as easy... >> >> >> I will reword my question. >> >> >> >> >> >> I've made a driver based on the pluto board and it's working >>on >> >>machinekit with >> >> >> raspi2 over spi and other altera boards. >> >> >> Partly works with beagleboneblack. >> >> >> https://github.com/tinkercnc/spi-fpga-driver >> >> >> >> >> >> And I asked if it would work with Lcnc. >> >> >> >> >> >> >> >> >> >> >> >> On 2016-02-03 03:24, Jon Elson wrote: >> >> >>> On 02/02/2016 06:24 PM, W. Martinjak wrote: >> >> >>>> How far is the development of lcnc on raspi/arm? >> >> >>> LinuxCNC has been running on the Beagle Bone Black for >> >> >>> several years. It is mostly the same codebase as LinuxCNC, >> >> >>> except for running on the Prempt-RT kernel (I think I got >> >> >>> that right). >> >> >>> The Beagle Bone Black has a pair of 200 MHz microcontrollers >> >> >>> that are used to handle step generation and other low-level >> >> >>> I/O tasks at much faster speeds than the Linux CPU can deal >> >> >>> with them. Great for software step generation. The Pi does >> >> >>> not have these microcontrollers. >> >> >>>> Would this [1] work with bare lcnc installation. >> >> >>>> >> >> >>>> >> >> >>> No, the regular LinuxCNC distribution is for an X86 >> >> >>> platform, only. Machinekit is the distro for the Beagle. >> >> >>> I think people have gotten it running on the Raspberry, but >> >> >>> the I/O on that board is VERY limited. >> >> >>> >> >> >>> Jon >> >> >>> >> >> >>> >> >> >>------------------------------------------------------------------------------ >> >> >>> Site24x7 APM Insight: Get Deep Visibility into Application >> >>Performance >> >> >>> APM + Mobile APM + RUM: Monitor 3 App instances at just >>$35/Month >> >> >>> Monitor end-to-end web transactions and take corrective >>actions >> >>now >> >> >>> Troubleshoot faster and improve end-user experience. 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