From the forum: Raspberry Pi review

in part review by DP | 11 comments

Here is a review of the Raspberry Pi from the forum:

This is my “home” forum for embedded stuff, as the community here is good. Though I note Raspberry Pi (here forward R-Pi) has its own forum (I’m teholabs there).

I wonder how many persons here got one? I ordered on day 1 (March) and just got mine this week… Eeppp. But I’m sure they will catch up in not too too long.

So I have some mixed feelings about R-Pi, on the one hand a lot of the fun of doing embedded system stuff for me is to see how much you can do with very little. People laugh at me when I tell them I have 512 bytes of memory for a project.

Read the full review below.

However, simple to use is good and always reinventing the wheel is not needed. While I like to code, implementing some protocol I didn’t design isn’t a lot of fun. Linux is a big big help there. I don’t have to port SSL/TLS for instance it is just there. This makes R-Pi a great way of being on the internet in a secure way. This is possible with my Procyon board as well but it isn’t as easy honestly as having an OS with a huge amount of software to throw at the problem.

I think a lot of people were expecting a lot for their 35 dollars (+ SD card + screen + mouse + keyboard; no so cheap now is it), investment… (though you can always SSH in ;-), but still need an SD card).

First impressions:

I started with Arch Linux, for a console application I think I would use Arch (at this point). At first it didn’t display anything over HDMI (I have it hooked to a TV). After a quick search I learned about the somewhat opaque config file.

R-Pi has a FAT boot partition. This holds the stuff that it needs to read for boot both kernels and configuration details. The configurations are all text files. The Arch image has a config.txt in this FAT partition. The file tells it to use HDMI_MODE=X (I forget the number but it is UK frequency). Thus my TV didn’t show anything, because it doesn’t support that refresh rate. I realized this when I did a quick google and found I should delete this file.

If you don’t have a config.txt it uses whatever mode the TV/Display wants. Okay great, only thing is it didn’t fill up my TV. To fix this you add overscan offsets to fill the rest up (In the troubleshooting eLinux FAQ). There is a post in the beginner section of R-Pi’s forum about HDMI modes (it is a big list). To start with though have no config.txt later you can add one.

After installing X and openBox on Arch (using VESA and fbdev as the video drivers) I decided to give another Distro a try, as it wasn’t all that smooth. I thought the recommendation was Fedora Remix based on some comment on the eLinux wiki. I have to say I did not find the Fedora remix acceptable at all. Performance was far worse than Arch subjectively. I then decided to try Debian’s image. This is what the “alpha” boards used.

It works quite well they were smart and used Midori and not Firefox and lots of other little things. I also note that Debian has a swap partition in the image while I know Arch didn’t and I don’t think Fedora did either. This could be why it runs better or it could be the kernel or maybe it is using a video driver other than VESA. I posted a question about this on the R-Pi forum but no answer as yet.

This might be Linux but a heavy distro full of software you don’t need like the Fedora Remix is currently is totally inappropriate for an embedded system.

I’m sticking with Debian for now using R-Pi and would recommend everyone use it for now at least, though no doubt progress will be rapid. However if I was done with a project that didn’t need a screen I might well go back to Arch for the no frills, configure everything base it has. I like that more for “I’m going to deploy this”.

Hardware:

The full datasheet for the BCM2835 is not public. Boardcom like Marvel is one of these companies that is highly unfriendly to anyone but volume people. I don’t honestly see how that helps them at all… But whatever the case may be a partial datasheet was released for the chip.

If you are used to micros this is the key stuff. Also Gert’s software for the Gertboard is that always helpful programming example to get started.

He nicely made it public domain, so we are free to crib from it. Though the pointers he chooses are a bit odd in places you can see what he does to get to the memory map for GPIO and things. Importantly he has basically handed everyone GPIO both in and output (with pull up/down), SPI, I2C, PWM and UART (though he doesn’t use it it is written down in the code).

The big difference here with R-Pi vs. regular embedded system programming is of course this isn’t embedded system programming by which I mean it is a program running on a OS with lots of processes and that OS is not a RTOS, so timing is not promised. This is a big deal and a big difference. I bet people will piggyback simple micros like AVR for just this reason.

I also think it will be interesting to see if/when someone does a RT-Linux flavor. They do exist.

I found getting started with the hardware not hard though and my first project is already under way.

Via the forum.

This entry was posted in part review and tagged , , .

Comments

  1. JBeale says:

    The eLinux wiki should be updated. Fedora Remix was initially recommended, but within a few days of its release, the significant bugs and usability problems caused it to be Not Recommended and it was removed from the R-Pi Downloads Page at http://www.raspberrypi.org/downloads

    You can see a discussion about open vs closed-source GPU drivers with JamesH (a Broadcom employee) here: http://www.raspberrypi.org/phpBB3/viewtopic.php?f=33&t=6188&start=25#p84117

    …still waiting for my own piece of the Pi.

  2. ginpb says:

    Debian rocks!!

  3. JesseJ says:

    Just a comment. The original author complains that Broadcom isn’t supplying the whole datasheet on the chip, but for many SoC solutions, the peripherals are one chunk and the original ARM datasheet is the other.
    He should be able to find the ARM 1176 reference/user guide to fill in the gaps, at the ARM website. After knowing the I/O and memory mappings, much of the rest will be software.

    IMHO

    • Brian says:

      I hope that is the case. But I do believe it was remarked when posted that it was a partial. NDAs are typical for Boardcom you have to give them a business plan and volume and all sorts of stuff for get full access. Such reserve is certainly not the the spirit of the DIY/maker/open hardware folks that this will be depending on.

  4. JBeale says:

    The Raspberry Pi uses the Broadcom BCM2835 SoC including the ARM1176JZF-S cpu core. The technical reference manual for that CPU is here: http://infocenter.arm.com/help/topic/com.arm.doc.ddi0301h/DDI0301H_arm1176jzfs_r0p7_trm.pdf

  5. asdf says:

    Reading various forums around the time of the first preorder round, there were a lot of people with higly unrealistic expectations of the Pi’s capabilities and who vastly underestimated the effort of working with a board like that right after release. I’m guessing a lot of the first batch will end up in desk drawers or on eBay, though I don’t know if the risk of getting a board damaged by static electricity is worth the $10-$15 you could save that way.

  6. JBeale says:

    I think some had overhyped expectations but you won’t save any money buying on Ebay yet. As of today June 4 2012, R-Pi’s are going for over 3x list price, http://www.ebay.com/itm/Raspberry-Pi-Model-B-Brand-New-/221038226220
    and even just an order code ( the right to purchase a new one at full price, delivery in ~5 weeks) went today for $11.

    • ewertz says:

      The average new board is going for about $100 on eBay right now — down from about $120-125 ten days ago and more like $140 ~3 weeks back. I doubt that they’ll sell for the retail price for at least three months.

  7. ray smith says:

    I have been in line too darned long to remain seriously interested in the r-pi….and glad I did not get in on the first batch, already moved the project over to an intel fly and happy about it….

  8. Steveh says:

    Initially I found rpi very interesting, however, if you dig a bit, you soon see that Raspberry pi is a bit of scam. It seems rpi has been created as a marketing ploy. Broadcom undercut and dump their commodity BCM2835 processor on the market through rpi, trashing vendors who supply normal linux OS chips (broadcom wont sell their chip to you, only to large corporate customers with a business model of cornering broadcom approved consumer markets). The raspberry pi foundation and their forums are plagued with broadcom employee’s, keeping the focus concise and in their favor whilst conditioning anyone seeking information (as they release close to nil info – so much for education). For an organisation declared as “Charity Commission for England and Wales” they are as much a charity as the fed is government.

    • ewertz says:

      None of what you’ve said is either news, nor is it unique to Broadcom. Nor are you alone in not loving the status of this CPU.

      It is not unusual for certain chips, especially mass-mass-market chips to only be sold to a few customers because they’re the only ones it was (originally) intended to be used by. TI does this with some of their OMAP products that are (were) targeted towards cellphone makers and the like. They may not even be documented to the same standards as general release/availability products as they work directly with the very few customers to whom it’s being sold. Pretty much all ARM and MIPS SoCs from China fall into this category.

      Many people are unhappy with the unavailability of documentation for this SoC. As long as RPi gets as many chips as they want at the prices they want, I don’t think that they or anyone else cares if they came from the clearance bin. It would (only? arguable…) be a terrible decision to use them if Broadcom only had a few hundred thousand of them left and no intention-of/obligation-to making more if RPi wanted them.

      In the end, noone’s forcing you to buy one, so you’re free to take a pass. Nor are you being forced to believe that Broadcom is doing the world any great favors for being part of the project. Noone but techies even knows that it’s a Broadcom CPU. You can bet if it was an Intel processor that you’d be subjected to an “Intel Inside” logo barrage.

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