Great update Dave. Very useful indeed. Paul
Sent from my iPad On 07.08.2013, at 21:26, David Bagby <[email protected]> wrote: > 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. Get down to code-level detail for bottlenecks, with <2% overhead. 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