Pi vs BeagleBone-Black

I'd like to add another pro for the BeagleBoard Black.

With the exceptions of the integer real time processors PRU-ICSS (not sure at this point why that is), and the PowerVR GPU for

well known reasons, the AM3359 technical documentation from TI is excellent to the point of overwhelming. The Technical Reference

Manual is over 4000 pages. No I did not accidentally add any zeros !

Gary Stewart wrote:

 

With the exceptions of the integer real time processors PRU-ICSS (not sure at this point why that is), and the PowerVR GPU for well known reasons, the AM3359 technical documentation from TI is excellent to the point of overwhelming.

You're right about the proprietary GPU, that seems to be an endemic problem for open source in the industry.  It's not true for the PRU-ICSS though.

The PRU-ICSS is fully documented in the Technical Reference Manual SPRUH73C, with the entirety of chapter 4 (250 pages) devoted to it.  Also, there is a full package of PRU-related materials on Github, including more documentation and source code of the PRU's PASM assembler, a Linux loader, demos, etc.  I've even checked that the assembler compiles and it does.

The BeagleBone materials on Github are at https://github.com/beagleboard/am335x_pru_package

The PRU has been used successfully in quite a number of projects as a quick web search shows, and this long predates the BeagleBone Black since the original BeagleBone uses a slightly different version of the same AM3359 SoC.

Morgaine.

Addendum: Repeating the link to TI's wiki pages on PRU which I gave in my first post on this thread, in case it was missed when looking for docs.  There is a developers' link at the bottom of that first page.

I noticed your interesting blog post about evaluating the Freescale Freedom-KL25z board. 

That's a very nice little Cortex-M0+ microcontroller and a well-featured board, especially for frugal low power standalone applications.  Have you tried linking it to the Pi for I/O expansion and better realtime response?  The very low price would seem to make it quite a good companion for the Pi, and your "easy to use" comments were encouraging, inasmuch as the barrier for budding engineers to get to grips with microcontroller programming would be quite low.

Morgaine Dinova wrote:

 

Gary Stewart wrote:

 

Original message:

 

The Unix model of operating systems just isn't designed for realtime programming, and no matter what realtime patches you apply or which realtime scheduler you enable (I've played with both), you're never going to get anything like the low response latency and absence of jitter that you can get from the cheapest of microcontrollers.  A far better approach is therefore to combine a bare-metal micro with a *nix system, and let the latter control the former with high-level commands which the micro then executes with very tight timing constraints.

 

That was an attack on the message. I can't help if you take it personally. As far as that and your far better approach goes see the remaining responses

 

You are deliberately misreferencing.  Your personal attack was not the comment on the above, but the comment below:

 

Gary Stewart wrote:

 

You really need to get better acquainted with real time Linux.

 

That has nothing to do with the subject matter, and everything to do with attacking the messenger.  Don't do it.

 

And then because your earlier personal attack wasn't enough, you did it again:

 

Gary Stewart wrote:

 

Perhaps you should go tell all of them that they are wrong. I'm sure they would value your opinion on that subject.

 

and again

 

Gary Stewart wrote:

 

I'm sure they would like to hear from you to set them strait on why it doesn't really work.

 

Just stop it.  Talk about the technical topic, don't criticise fellow forum members when you reply to them, it adds nothing to the discussion.

 

Your technical comments are welcome, and interesting.  If you disagree with an observation, just say you disagree and provide contrary evidence.  You don't need to attack the messenger as part of your rebuttal.  It's not a valid form of engineering discussion.

  You are deliberately misreferencing.

No, you are. The statement:

  The Unix model of operating systems just isn't designed for realtime programming, ...

the "attack":

You really need to get better acquainted with real time Linux.

Pretty sure that is a response to the message not an attack on the messenger and directly related to that statement, subject matter or not.

  Just stop it.  Talk about the technical topic, don't criticise fellow forum members when you reply to them, it adds nothing to the discussion.

Does your regular use of fanbois or Raspberry Pi fanbois in completely non-technical posts of yours count as criticizing fellow forum members ?

We're not doing a tutorial, but we are discussing the technical merits of different approaches to achieving realtime performance in an embedded Linux system, and there is not the slightest doubt that the realtime performance of realtime Linux is very poor compared to that of any old bare metal embedded microcontroller.

Not sure how discussing hard real time jitter relates to discussing the performance of real time Linux compared to any old bare metal processor. Seems like it would be more appropriate if we were discussing real time Linux performance verses

any other full feature RTOS performance (apples to apples).

Your technical comments are welcome, and interesting.  If you disagree with an observation, just say you disagree and provide contrary evidence.

I do, and you do your best to ignore it. Well until now at least.

I agree, it is always dependent on the realtime requirements of an application, and a poorly performing realtime system may well be good enough for an application that has only weak realtime requirements.  There are undoubtedly many applications for which the 100us or so latency and unspecified jitter of realtime Linux is perfectly adequate, or at least acceptable.

OK, thanks ? But excuse me if I add that the quality of the performance is in the eye of the people building the application and the performance of the application itself not what negative spin you

want to put on it. Your continual use of damming with faint praise, adding "poorly performing", "weak realtime requirements", and "at least acceptable" to your sentences are classic examples,

clearly show bias on your part. You keep using absolute terms (always negative) to describe relative qualities (for the dependent part). The poor performance you speak of is prettymuch in line

with most commercially available full feature RTOS's given equivalent hardware and the weak real time requirements are common to a lot of applications. I'm not sure how, technically speaking of

course this makes them weak and I'm sure that the commercial RTOS people would hotly dispute the description of their RTOS as poorly performing.

We're not doing a tutorial, but we are discussing the technical merits of different approaches to achieving realtime performance in an embedded Linux system, and there is not the slightest doubt that the realtime performance of realtime Linux is very poor compared to that of any old bare metal embedded microcontroller.

Not sure how discussing hard real time jitter in Linux relates to discussing the performance of real time Linux compared to any old bare metal processor. Seems like it would be more appropriate if we were

discussing hard real time Linux performance verses any other full fearture RTOS hard real time performance (apples to apples).

You seem to be disputing the quantitive study that I linked because it used high-end machinery, but high-end machinery will almost always yield better performance in a realtime operating system simply because everything runs faster, so I can't agree with your dismissal of that study.

No, I clearly disputed the study because it was for enterprise class servers which is not even close to a typical real time application, and it did not use hardware that was even close to typical hardware. I now add that it was not a

hard real time test even though you used it as an example for explaining hard real time jitter problems and the test results for one particular version of non-hard real time Linux optimised for the enterprise server environment does

not tell me anything about others that are optimised for more general hard real time and real time applications.

I agree Mark.  This thread has lost focus. 

It WAS about a comparison of the Raspberry Pi to BeagleBone Black and how we'll use each.  Now we have gotten down to Real Time OS and FPGA like abilities.  95% of the market is going to use BOTH boards for hobbies and prototyping.  I was one of the first people to say my preferences (RPi Model A for small stuff because of power consumption and BBB for large projects because it has more of the features I'm looking for like IO.)

I would say lets fork the BBB technical talk to another thread (maybe in the BeagleBone forum) because that seems to all this is now.

Morgaine

Not yet, as I'm waiting for the headers to arrive. Silly me expected jaycar to carry them, but no...

I did order 3 more to go with the ione E14 sent. How could you resist.?

An expansion board is lacking as well, which is a shame as the number of I/O make this better priced than a Mega.

I have a cunning plan, but need to sit down and discuss it with someone for doing the boards and then selling them to make them very affordable.

If you've been following the top members forum, you'll also see that currently mbed.org is my best option for programming it, and someone has kindly done half a library that allows the existing arduino sketch to be used.

I've ordered another Pi interface so eventually it will get connected, or a normal arduino and this used as a remote using the built-in accelerometer and touch slider.

Cheers

Mark

Ervin Kosch wrote:

  I was one of the first people to say my preferences (RPi Model A for small stuff because of power consumption and BBB for large projects because it has more of the features I'm looking for like IO.)

I'm curious what your power consumption figures are like for the model A as the BBB SRM has some interesting power consumption figures that on paper appear a good deal better than the B under somewhat similar circumstances.

Ervin

I'm all up for a good debate, however this (from an outsiders view point) has turned into something else, resembling kids squabbling over he said, she said.

I think everyone needs to take a deep breath, and quieten down.

I've seen a written sentence interperated different ways by different readers before, and neither reader got it right, because that wasn't the way it was intended.

It just so happened that the writer hadn't phrased it as well, hence it wasn't as clear as they intended.

I'm sure both boards will have their place in our world, and one might be favoured over the other for xyz reason(s).

I haven't seen a direct comparison between the both to enable a begineer to make choices.

I'm sure that with all the intellect in this group, we should be able to draw up a chart, so that someone could do that, and yes price may be one factor.

So how about it people?

cheers

Mark

Mark,

> I haven't seen a direct comparison between the both to enable a begineer to make choices.

There is a summary comparison for beginners here:

   http://www.raspberrypi.org/phpBB3/viewtopic.php?f=63&t=41489&start=81

I found user gyeben's response interesting, which says:

     "Took a look at the article mentioned in the first post (http://roboteurs.com/beaglebone-black-vs-raspberry-pi/) and that article is clearly unfair to the Pi. 

        | Some people have clocked the Pi up to 1Ghz but its pretty risky.

     It's NOT risky. Overclocking the CPU is not risky at all."

Mark Beckett wrote:

 

I'm all up for a good debate, however this (from an outsiders view point) has turned into something else, resembling kids squabbling over he said, she said.

 

I think everyone needs to take a deep breath, and quieten down.

 

...

 

cheers

Mark

The following comment is to be taken humorously and with hopes that this shadow hasn't offended:  It does seem to the casual observer that some of the above discussion appears to be arguing-for-the-sake-of-arguing rather than a productive exchange of ideas.  Personally, some of it calls to mind a Shakespeare play in which a young man and a young woman are constantly sniping at each other through the first few acts but then they realize that all the arguing is really because of repressed sexual tension and that they're really in love with each other and become an item at the end.

Hmm, now what was the name of that play?

coder27 wrote:

 

Mark,

> I haven't seen a direct comparison between the both to enable a begineer to make choices.

 

There is a summary comparison for beginners here:

   http://www.raspberrypi.org/phpBB3/viewtopic.php?f=63&t=41489&start=81

 

I found user gyeben's response interesting, which says:

 

     "Took a look at the article mentioned in the first post (http://roboteurs.com/beaglebone-black-vs-raspberry-pi/) and that article is clearly unfair to the Pi. 

        | Some people have clocked the Pi up to 1Ghz but its pretty risky.

     It's NOT risky. Overclocking the CPU is not risky at all."

Here's what I wrote at in the same RasPi forum discussion:

What are some of the things you get for that extra US$10 versus RasPi?

 

Faster processor: 1 GHz Cortex-A8 versus 700 MHz ARM11.

Far more I/O pins.

Ethernet that connects directly to SoC instead of over USB.

Two RISC engines for low-level programmable I/O.

BBone white has rounded corners so it actually fits in an Altoids box.  I think BBone black is the same form factor.

 

According to my observations, I would say RasPi has better community support so is a better choice for new users.  IMO Beagle has always targeted developers rather than users -- I don't know if there will be an effort to change that.  Also, it may only be my own impression.

 

[Edit: Beagle does have good community support -- it just seems to me that RasPi's is better and that it's easier for a new user to get up to speed with RasPi than Beagle.  For example, it's easier with RasPi to find a recommended OS version and install it.  JMO/YMMV]

Today I would also add that BBone Black has 2GB eMMC on the board which is pre-loaded with Ångström so it boots right out of the box and is immediately useful.  BBone's Cortex A8 supports other GNU/Linux distros such as Ubuntu which haven't been ported to RasPi.  (Personally, I prefer the Debian on RasPi to Ubuntu on my x86 PC -- chacun a son goût.)

OTOH, for video RasPi's media processor is probably better.  Like Morgaine, I have no need for it so it's not an advantage.

Also, I wrote the above comment before discovering that beagleboard.org had just reformatted their web site and it appears now to be a lot easier to get OS distros (for example).

Luc, Mark and Ervin, I agree completely about the pointless digression into realtime Linux.  That's why I didn't respond to the latest salvo, it's clearly a non-productive argument, so I ended the interchange unilaterally.  The merits or otherwise of realtime Linux are entirely irrelevant to the discussion about BBB versus Pi.  I tried to end it through reasoned discussion, but that failed.  Sorry.

In contrast, the BBB's PRUs are entirely relevant in the comparison, because it's a salient built-in feature of the BeagleBones and is so powerful that it has front-page bullet points on beagleboard.org's BBB page.  It's clear that they rate it highly, and not discussing it in a comparison with Pi would be remiss.

Also, let's not forget that even Eben Upton has publicly expressed support for the idea of coupling the Pi to an Arduino.  He's an engineer, and he knows full well that the gains in interface expansion and in realtime performance are really quite enormous when you combine the two.  Even the Gertboard has a microcontroller on-board, and despite not being an RPF product, it certainly has their blessing.

Well, because of its PRUs, the BBB requires no additional microcontroller to achieve the same kind of gains in interface expansion and realtime performance, so this enters very strongly into the comparison.  Pi can handle a small amount of interfacing without additional hardware, whereas BBB can handle a lot more.  Pi can satisfy very very weak realtime requirements with its standard kernel, whereas BBB can meet very hard realtime constraints with its standard kernel because it has a couple of PRUs that are dedicated to I/O.  For ambitious applications, that's a very big deal.

PS. This was about one feature only, where BBB happens have superior functionality.  Both boards do of course have both pros and cons, that's very clear, and it means that there is no "best board".  There is only "best board for your particular requirements", and so the answer will vary with the person.

Morgaine.

Luc, Mark and Ervin, I agree completely about the pointless digression into realtime Linux.  That's why I didn't respond to the latest salvo, it's clearly a non-productive argument, so I ended the interchange unilaterally.  The merits or otherwise of realtime Linux are entirely irrelevant to the discussion about BBB versus Pi.  I tried to end it through reasoned discussion, but that failed.  Sorry.

In contrast, the BBB's PRUs are entirely relevant in the comparison, because it's a salient built-in feature of the BeagleBones and is so powerful that it has front-page bullet points on beagleboard.org's BBB page.  It's clear that they rate it highly, and not discussing it in a comparison with Pi would be remiss.

Also, let's not forget that even Eben Upton has publicly expressed support for the idea of coupling the Pi to an Arduino.  He's an engineer, and he knows full well that the gains in interface expansion and in realtime performance are really quite enormous when you combine the two.  Even the Gertboard has a microcontroller on-board, and despite not being an RPF product, it certainly has their blessing.

Well, because of its PRUs, the BBB requires no additional microcontroller to achieve the same kind of gains in interface expansion and realtime performance, so this enters very strongly into the comparison.  Pi can handle a small amount of interfacing without additional hardware, whereas BBB can handle a lot more.  Pi can satisfy very very weak realtime requirements with its standard kernel, whereas BBB can meet very hard realtime constraints with its standard kernel because it has a couple of PRUs that are dedicated to I/O.  For ambitious applications, that's a very big deal.

PS. This was about one feature only, where BBB happens have superior functionality.  Both boards do of course have both pros and cons, that's very clear, and it means that there is no "best board".  There is only "best board for your particular requirements", and so the answer will vary with the person.

Morgaine.