Date: Wed, 07 Aug 2013 16:01:32 +0300 Paul Lacatus wrote: My problem is that I need more info about LinuxCNC on BB(W/B) that I hope to find here on the mailing list . This other questions still remains: 1. Is this card ( BBW 720MHz 256 MB ) strong enough for running LinuxCNC headless ? Or should I get a BeagleBone Black (1GHz / 512 MB ? ______________________
Hi, Your request for more information made me realize that the info that those of us working in this area take for granted may not be obvious to others - So, here is some info re LCNC and Beaglebones that may help provide some context to people considering LCNC on beaglebones. There are two Beaglebone boards currently available. The original was just called the Beaglebone and it has white silk screen. The newer member of the family is the Beaglebone Black and it has black silk screen. The introduction of this "Black" product caused people to start to refer to the original as the Beaglebone White. As the boards names are both long and a bit confusing in conversation, many have started to use BBW and BBB as unambiguous abbreviations. Here are some of the significant differences between the boards from the LCNC viewpoint. BBW: US $89 No onboard video output Runs From SD card Runs on a 3.2 kernel BBB: US $45 HDMI output (can run LCNC GUI - though unclear how well - I'll come back to this) Runs from onboard Flash (eMMC) Also has a SD card slot Runs on a 3.8 kernel Essentially all the ongoing work I'm aware of is for the BBB. There seems little interest in further development for the BBW over the BBB. The difference in kernel levels between the boards means that there are major differences in how you set up the hardware at boot time. (3.2 uses board files, 3.8 uses device trees). This change is a Linux kernel thing and is something that just needs to be dealt with. The change just happened to fall in time/revision between the BBW and BBB releases. Eventually this will be less important, but we in the transition period and this has impacted BBB hardware support. LCNC (2.6pre) is running on the BBB using extensions that have not yet made their way back into mainline LCNC. (they are available from repositories with forked and experimentally extended versions of LCNC) The BBB extensions include the need to use a custom 3.8 kernel that uses Xenomai instead of RTAI. One should realize that today, working with Beaglebones (or any ARM based platform) and LCNC puts you on the bleeding edge of development. IMHO, if one's primary interest is running a rock solid stable CNC machine today, it's probably better to use a x86 platform. OTOH, if one wants to play with LCNC development, come join in the fun. Overall IO capabilities are very similar between the two BB boards. The addition of HDMI and eMMC to the BBB used pins (default config) that were avail for IO on the BBW. The BBs (both the BBW and the BBB) have connectors for "Capes" (I.e. extension boards). Some type of extension board interface between the BB and the outside world is desirable to shift logic levels between the BB levels (3.3v) and the outside world. The LCNC oriented capes also provide additional electronics to interface to the raw IO pins of the BBs (Motor drivers, temp sensing circuits, RS485 etc). Many Capes that were designed for the BBW (before the BBB was released) happened to use pins that became allocated for HDMI or eMMC on the BBB. This makes those capes incompatible with the BBB (as the BBB is configured out of the box). This resulted in two types of activities: a) redesign of capes to create new versions that work with the BBB b) Put a "pin scrambler" adaptor between the BBB and the BBW cape. One example of this is the "Bridge" adaptor that the BeBoPr author used to make his BBW board work on the BBB. c) Additional new designs are/have been being done for the BBB. In all cases significant new software work also had to be done to create the 3.8 kernel device tree support needed to boot the hardware. AS of today, many BBW capes have versions for the BBB - but probably not all (I've not checked in a while). The lack of video on the BBW means that you pretty much have to run LCNC headless on this board (unless you spend additional $ on a video cape for the BBW). The BBB is 1/2 the price of the BBW and does not need a video cape - that makes it more cost effective. OK, what about graphic performance of the BBB? In particular, is it good enough to run Axis on the BBB? The current situation is that the BBB has HDMI video out. The BBB also has some graphics acceleration hardware in the chip used in the BBs. Alas, the video driver for the BBB does not use the hardware acceleration. The result is that the BBB video performance is not as good as it could be. This should improve over time. Is the performance good enough today to run Axis? That is not clear right now. (BTW, I've not tried gscreen yet) I'm running LCNC on a BBB with a K9 Smorgasboard cape, driving a Shapeoko router that I use as a test bench setup. When running axis, much of the time it seems ok. However, sometimes, there are hesitations and irregularities in the gcode movements. The motor sounds change and it becomes real obvious that motion stops being continuous. If I switch to TKEMC the oddities appear to go away. That may be telling me that there is a CPU load problem that AXIS exacerbates. But it could be things totally unrelated to axis - for example LCNC is running from the SD card for this setup. Honestly, I don't yet know what the glitches are, or the root causes. I haven't done enough testing to isolate things to be able to draw any firm conclusions. Such is life when running bleeding edge hardware and software. Anyhow, I hope this narrative can provide a bit of context for those thinking about using a LCNC/BBB combination. Dave ------------------------------------------------------------------------------ Get 100% visibility into Java/.NET code with AppDynamics Lite! It's a free troubleshooting tool designed for production. 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