Hello, is it me you're looking for?

Elegant simplicity. Those were the days *sniff*.
(Atari 800XL emulated with Atari 800 Win PLus)

It never ceases to amaze me how satisfying "Hello world!" can be.

It seems so trivial now, but way back in the proverbial day the shortest BASIC program felt like a triumph.

Nearly 30 years on, the language may have changed but it's still satisfying proof that you can get something to work. In this instance it took seconds to write some C++, a couple of hours spread over half a week to work out how to cross-compile from Ubuntu to Rasbian. The relief at finally seeing those immortal words was immeasurable. Could be worse I suppose - it took researchers two years to write the first non-trivial program in Malbolge.

Virtual machine, Makefile, C++, compile, SFTP, SSH session,
and it's done. This is progress, people! Or horses for
courses, you decide.

To cut a long story short, the ARM cross-compile toolchain in the Ubuntu repos is set up for ARMv7 onwards whereas the Raspberry Pi has an ARMv6. With just a few parameters in the makefile you can tell it to compile for ARMv6 with hard float, but you also need to get hold of some ARMv6 static libraries - I just copied them over from the RPi. There's a toolchain on the Raspberry Pi repository on github which already has the correct parameters and libaries, but it's 32-bit so I had to install some 32-bit libraries to get it to run on my 64-bit Ubuntu virtual machine (libc6-i386 and lib32z1 if you're asking). It worked on 32-bit Ubuntu with no fiddling at all, but it took me a week's worth of evenings to figure that out.

This is all well and good when I'm only using the most basic libraries which come with the toolchain, but to do more interesting stuff I'll be needing more libraries. I still don't think I've found the ideal solution to this: at the moment I'm rsyncing the Raspbian libraries over from the Raspberry Pi. Compiling libraries from source seems a bit of a wasted effort. I wonder if I can set up APT to get the Raspbian libraries directly from the repo?

I've managed to get the core part of my OpenGL screensaver working on the Raspberry Pi now. It's incredibly slow, and I think that's because I'm using the OpenGL libraries which aren't supported by the GPU, so it's using the Mesa software drivers instead. To use the GPU I'm going to need to switch to Open GL ES and EGL, and that's a whole new can of worms but it's ultimately what I wanted to do anyway.

So it's been a bit of a frustrating fortnight, I've broken my update-a-week guideline, and spent too much time floundering around trying to understand the infrastructure with too little tangible progress. Having said that, floundering around for a while is fine so long as something is learnt in the process, and I think I've learnt a lot more about the GNU C++ toolchain, in particular the linker. Hopefully I'll start getting my head round OpenGL ES soon, I think it's mostly the same as regular OpenGL and it's just a matter of appreciating the differences.

We are dancing mechanic

Just as I've started thinking about making a board for a Raspberry Pi based robot, someone goes and makes the mother of all robotics boards - the Gertboard. Curse you Gert Van Loo! Actually it's a very nice piece of kit, but it's bigger and more expensive than the Raspberry Pi itself, and I don't think it's really what I want. It's given me a few ideas though.

Some circuitboards, yesterday

The most powerful component on the Gertboard is the Atmel AVR microcontroller, which is the same chip that's at the heart of the Arduino, but it seems like overkill for my purposes. Do I really need a microcontroller on the robot when I've got a Raspberry Pi sitting next to it? It's cheap, and looks like it's got on-chip D/A converters so I could probably use it to drive the motors with variable speeds, but if I wanted that I could do it more simply and cheaply with my own circuit.

The Gertboard manual suggests that you can vary speed with pulse-width modulation (PWM), but the problem is that the Raspberry Pi only has one part-time PWM output and the switching on the GPIOs isn't fast enough for me to do botched up PWM on those. Maybe one PWM output is enough though - rather than connecting four GPIOs to the motor controller inputs, use the GPIOs to gate the PWM input - yeah, that'd work.

I'd been looking at a separate motor controller board, but wouldn't it be neater and cheaper to put a controller chip on my own board? The Gertboard has an L6203, but that's more expensive than the controller board, is specced way beyond what I need, and only has one channel whereas I'd like two. I'll have to look around and see if I can find the same IC that's on the controller board, or something similar. Would PWM work with the motor controller? Gert reckons it will with his board, and who am I to argue?

Wearing a bra on your head while working on geek
projects turns them into Kelly LeBrock. That guy
should know, he's Iron Man FFS.

Now I'm trying to remember the circuits to do some of these things, but I've forgotten pretty much all of the analogue electronics I learnt at college. Thankfully the intaweb is helping to jog my memory a bit. If I do want variable speed, gating a PWM signal should just be AND gates so that's easy. But I'll probably want something to convert that to a stable DC analogue voltage, which is... an integrator? Can the motors take a PWM input? The GPIOs are 3.3V and the motors take 6V, so I need to step that up and be able to supply up to 2A for each motor. An OP-AMP with positive feedback isn't going to supply enough current so I'll need a hefty power transistor in there... whaddya know, I just re-invented the Low drop-out regulator... Is there an off-the-shelf LDO which lets you provide a variable reference voltage? That's basically what's in a motor controller, so I've come full circle - might as well just get one of those.

As I'm so out of practice with boards I'm a bit apprehensive about doing a complicated board in one go. It's tempting to do a smaller board first, or at least do a larger board in phases and test it between each phase. Just getting battery power to the RPi via a switching regulator would be a good start and confidence boost. At the very least I've got to start getting some schematics drawn up, not worry about exact capacitor values or board layout yet, but just start turning the morass of nebulous ideas into something a bit more coherent.

Whatever I do with the robot, it's going to need some software so that's where I'm spending my time at the moment. I'm trying my hand at cross-compiling as it's going to be faster than compiling on the RPi itself, and it's also harder than a native compile so more interesting. As I've been playing with DOSBox recently I downloaded the source for that, got the Raspbian toolchain and... wait a minute, where's the Makefile? There's a Makefile.am and a Makefile.in, what're they? Turns out they're for the GNU Autotools, which I've never used before.

Learning how to use those and how to cross-compile was a bit much to take on in one go so I took a step back and started with "Hello world". Once I'd mustered the presence of mind to write 5 lines of code which actually compiled natively, I'd got the right toolchain for compiling C++ from Ubuntu to the Raspberry Pi (g++-arm-linux-gnueabihf seems the best bet), and I'd sorted out the libraries, I got an executable which I FTP-ed over to the RPi, SSH-ed in, ran the executable, aaaand.... segmentation fault, my old friend. Next time my "Hello World" is just going to print "Segmentation Fault" so it'll look like it worked whether it did or not. It's barely worth opening up gdb, with a program that simple it's going to be a linking issue so it's probably just a matter of getting the right options in the makefile.

In other news, I've continued getting things to work on DOSBox. Speedball 2 works very nicely, it sounds absolutely awful but early PC games always did. I got UFO: Enemy Unknown working briefly but it was very slow and after I'd faffed about with the config it stopped working. It looks like I should give up on protected mode games until protected mode is improved, which it probably never will be, or DOSBox starts using SDL 2.0 with its improved use of OpenGL. And it seems that others are having much more luck with MAME than I did on my half-arsed attempt, so maybe I'll give it another go one day.

We've only just begun

I finally got a chance to play with the Raspberry Pi and it's been a doddle to set up so far.

After reading some of the horror stories, I half expected some problems getting the RPi to start up at all but thankfully had none. I guess my paranoia helped as I'd read all about the power issues, purchased a half-decent power supply and a really good powered USB hub.

My only video option at the moment is composite to my telly. Yes, I know most self-respecting gadget-philes bought HD flatscreens with HDMI years ago - myself and my partner both bought 21" Sony Trinitrons over a decade ago, we don't want to get a new telly until at least one of them expires, and the damn things are just too well-built, refusing to die. I'm using a composite + phono to SCART adaptor, combined with composite and 3.5mm to phono cables running from the RPi, and the picture isn't too bad. There's a bit chopped off the left-hand side, the interlacing looks awful sometimes and text in a terminal window is a bit blurry, but it's generally good enough for most stuff and it'll do until my HDMI-DVI adaptor turns up.

Bear in mind that though I've had close to 20 years of experience as a UNIX/Linux user, I've not really done much in the way of installs or admin beyond switching window manager. I've installed Ubuntu on my netbook about a million times, but that practically installs itself. I've been learning as I've gone along, trawling the intaweb for guides, supplementing them with a great deal of educated guesswork and trial-and-error.

For the Raspberry Pi I'm using Raspbian, as it's now the recommended Linux distribution and the optimisations are coming thick and fast. At initial startup there's a config utility to help sort out the important stuff. I'm not going to be doing anything clever with graphics yet, so memory's shared 7:1 between CPU and GPU. I thought I'd give the LXDE window manager a go to start off with, but at PAL resolution it looked a bit cluttered and with the interlacing it was a little too reminiscent of Amiga Workbench for my liking, so I turned it off again and turned on SSH.

SSH just worked, with no fuss whatsoever. I got the IP address from my router (though "ifconfig" on the RPi also does the job), put it into PuTTY and that was it - remote access to the RPi. Xming was also fairly easy to set up without really knowing what I was doing - initially the RPi's IP address was being blocked so I added it to Xming's X?.hosts file, set the $DISPLAY variable, et voilà. Then I undid all that and set up X11forwarding in PuTTY to sort out the display for me. Wireless was a lot more tricky to set up, but once I'd read a few guides (the debian one was the most useful), convinced myself that the dongle wasn't broken, figured out that you need to be root to scan for interfaces, learnt the syntax of the interfaces file, realised that WPA needs a completely different set commands to WEP, and worked out how to generate a PSK, I was up and running.

Setting those things up meant I could remove the mouse and keyboard, disconnect the telly, and unplug the Ethernet cable tying it to my router. I've now got the RPi on my desk instead of a footstool by the telly, with just the hub/wireless plugged in. It's a useful setup for playing around, getting better stuff set up, taking screenshots, perhaps natively building C++, but what to try first? For low-effort instant gratification, how about some old games?

Tiny amount of activity in game, sshd CPU usage spikes

I mentioned Beneath a Steel Sky in my previous post, and that's free on ScummVM so I gave it a go... perhaps unsurprisingly it was very, very slow over a remote display and there was no audio. When I switched back to using the telly it was nigh perfect and really fast, huzzah! There was the odd crackle and pop over the speakers, though I've no idea whether that was the SCART connector, phono cable, socket, board, drivers, feedback from the USB hub or just the incessant ALSA underruns you get with a busy CPU. Back to the SSH connection again I could see the CPU usage of the sshd (SSH daemon) process spike when anything moved. Turning off X11forwarding and going back to insecure X?.hosts/$DISPLAY didn't make much difference, but VNC was a bit better.

It took over an hour just to get to kick-off for this
screenshot

Next up, Sensible World of Soccer running on DOSBox. First job: finding the CD, which took a while as it was in storage, in one of the many boxes of stuff we rarely use in the spare room. You may be shocked to learn that the Raspberry Pi doesn't have a native CD drive, and I don't have one with a USB connection, so I tried to find an ISO maker which was a) free and b) actually worked. Eventually I settled on ISODisk, which was a bit flakey but did the job nicely. Once SWOS was running it was ridiculously slow with Xforwarding, and didn't work at all with VNC. On the telly there was a keyboard issue, but once I'd sorted that out it was still rather slow. It could probably be tweaked a bit, but SWOS runs in protected mode which is notoriously slow on DOSBox so I think the RPi's 700MHz processor doesn't quite cut it. That's a shame, I was quite looking forward to having SWOS on a little box under my telly - though I've discovered that there's a Wii version of DOSBox available...

I've also had a look at MAME, but there's some weird video driver issue I'll have to get to the bottom of. If I do get it working, I'll really want to get my gamepad working too but that looks a bit tricky under Linux. It's a Microsoft gamepad, so what are the chances of an official Linux driver?

Perhaps trying to use the Raspberry Pi as an emulation machine is a bit optimistic as its processor isn't great. All the graphics is going through the CPU, most emulators don't take advantage of the GPU. ScummVM works well but as I understand it that's not really an emulator, it's a new implementation of the interpreter. But it's been a useful exercise in just getting stuff working and probing the limitations of the box. For my next trick I think I'll try something a little more suitable. Maybe I'll learn how to use OpenGL ES? Well lookie here, the Quake II source code...

Domo Arigato, Mr Roboto

I apologise if my first post was incomprehensible to non-technical people. I did try, but it's not easy to accommodate an audience ranging from university Electronic Engineering lecturers to drama graduates - I'm torn between getting lost in jargon and getting bogged down explaining what things like SSH are. I suppose I could provide some hyperlinks?

When I ordered a Raspberry Pi I was told I'd have a six week wait, but against expectations I got it 10 days later. The trouble is that I ordered parts with long lead times, thinking they'd still turn up before the RPi, and a lot still hasn't turned up. Two key components are missing - a power supply and an HDMI-DVI adaptor. I think I can use my iPad charger temporarily, and get by with composite video to our aging telly, but I've not had time to try yet due to spending the last couple of days being ill and a dad.

Ooh I see evil...

I've been thinking some more about a robot project, though at this stage it's still about checking feasibility and costs without too much detail. The RPi will be the heart of it, connected by the GPIOs to an off-the-shelf motor controller, possibly via something to protect the RPi, that much is straightforward. As I see it there are two main problems to solve: connectivity and power.

The robot needs to provide some kind of remote access to the RPi for a telnet or ssh session, and preferably a fast enough link to send back real-time lo-res video. Wi-fi seems like an obvious choice for this but the RPi isn't designed to support most USB Wi-Fi dongles without a powered hub. It's designed for "low-power" devices, taking no more than 100mA - the "unit load" in USB 2.0. The polyfuses used on the USB ports are rated at 140mA, and they have quite a bit of resistance so at high currents the voltage supplied can drop significantly below 5V. You can perform what's called a PiPass, short-out the fuse with a small resistor, but I'd rather not solder stuff directly to my RPi if I can help it and reckon fuses are generally added for a good reason. So my options are:

1. Find a Wi-Fi dongle which draws less than 140mA, can tolerate a supply drop of about a volt, and has a linux driver compatible with the RPi's ARM processor.
2. Use a Y-cable to connect to both USB ports.
3. Feed external power into the Wi-Fi dongle.
4. Use a different type of connection.

Would a low-power dongle compromise on range and signal strength, so drop-out more easily? I'm yet to find one which I'm certain will work. I recall reading somewhere that Y-cables violate the USB spec and I'd kinda like having the other port available, so I'm leaning towards option 3. What's needed is effectively a mobile 1-port powered USB 2.0 hub. Could I put together something which supplies the power without knackering the signal integrity of the data lines? As the data lines are a twisted pair I guess they're completely independent of the power rails, but is the shielding connected to ground? Though it should be a short trip from the RPi's USB port, over a cable which is maybe 10cm long to a new port, at 480 MBit/s does it still have to be treated as a transmission line with matched impedance? Perhaps I'm just being paranoid and it'll be a cinch, but I'd better dig out the spec to answer some of these questions.

Ideally everything would be powered off a single battery pack. The RPi can be powered over GPIO, it needs a steady 5V supply and can draw up to 1.2A. The motors I'm looking at each take 6V and have a 360mA stall current, and that's just for the low power versions - HP ones stall at a whopping 1.8A, though if I could provide that the extra speed/torque would be tempting (200cm/s? Practically light speed). Power also needs to be provided for the motor controller and connectivity in whatever form it might take. Will four AA batteries be up to the task? Rechargeables can do about 2500mAh, I doubt I'd get much more than an hour out of them even if the power were consumed really efficiently, but it'd depend on how much work the RPi was doing and how much the motors were moving. As a battery drains its voltage can vary quite significantly, so I'll have to use regulators and if I do that I might as well go with something mightier and step it down to the right voltage(s).

So I'm looking at putting together a custom board to do those things. Though I might be able to get away with one voltage regulator, I expect I'll need two - one giving me 5V for the RPi and the extra USB power, the other giving me 6V for the motors and controller. The RPi will need a switched supply to keep a nice, steady voltage, I might get away with a linear regulator for the motors but if there's a controller on the same circuit I'd have to check that could take a voltage drop, and a switched supply would be more efficient, helping prolong the battery life. I'd also like to detect when the battery voltage is getting low so I can cut off the motor power, with luck keeping the RPi up long enough to shut down cleanly.

Making a board like that should be well within my abilities. At college our end of year one project was to make a switch-mode power supply, and though IIRC I only got a C that was pretty good for the marker I had. That was running off the mains, so it had a step-down transformer and rectification which I wouldn't need for this project where it'd be DC-DC. My worry is that as I've gravitated towards digital electronics I've learnt a lot of theory but not really had much experience with boards or more practical considerations like impedance matching, decoupling capacitors, etc. Still, half of the point of this project would be to re-acquaint myself with all that stuff.

Once I've recalled enough of my college education to pick the right resistor and capacitor values, I'll just need a stack of soldering kit, bit of Veroboard™ and a bunch of components, just like the good ol' days. Then I need some time to spend on it. If Micro Men is to be believed Steve Furber single-handedly soldered the Acorn Proton prototype overnight, but the guy's a god among men. Still, once I've finalised the design I should be able to put it together in a couple of hours I reckon.

I'm also wondering how to make it more than just an over-complicated RC car. It'd be good to add a camera, even if that proved to be no more useful than helping me find things I'd stored under the bed. It'd be really good if the robot could process the images and do its own path-finding, but creating a model of the world off a single camera is pretty hard. I could add a pump and a bag for the world's smartest Roomba™? That reminds me - anti-stair sensors might be an idea as that's how my BigTrak met its demise...


Finally, I was thinking about naming the robot. For some reason "Harvey" sprang to mind immediately, I've no idea why. It'll be a wall-banger of sorts I guess. I also like "Joey", after the robot from Beneath a Steel Sky who starts the game as a small card and gets inserted into different chassis as the plot progresses. There's also "Nigel", the robot from Gozilla: The Series who gets destroyed every episode. Any other suggestions welcome.

Hello, good evening, welcome to nothing much

Welcome, gentle reader, to my blog of adventures in geekery.

Since I heard about the Raspberry Pi project I've been getting progressively more and more excited about it. I'm of the same generation as the RPi's creators, the generation of bedroom programmers and electronics hobbyists who grew up to become the engineers of today, so I can appreciate what they're trying to do with it as a way to introduce kids to programming. But it's also a great platform for more experienced tinkerers to play with, as it can easily be powered by batteries and at under £30 you don't have to be too worried about breaking it. The early adopters have had their RPis for a while now and come up with some great projects like this one. 

Due to the somewhat distracting arrival of our second child I've not pounced on the RPi as quickly as some, and by the time I'd registered my interest there was a waiting list before they'd even take a pre-order. But the orders opened up earlier this month and I placed mine last week, apparently it's now been dispatched so I'm getting giddy with excitement. Unfortunately the RPi doesn't currently come with all of the bits and pieces you need to get started, you need to order those separately and I'm going to have to wait for those. There's not much I can do without a power cable and the one I ordered isn't due for a month (!), so I'll have to see if I can use my iPad's mains to USB adaptor until the dedicated one turns up though I've seen some reports that it's been found to be inadequate. I've not ordered a powered USB hub as the decent ones are more expensive than the RPi itself, though having read a bit about power requirements and polyfuses I'm not so sure I can get away without it. Hub or hubris?

And that brings me clumsily to the point of this blog - essentially a lab book with style sheets, to keep track of my Raspberry Pi projects and other geeky projects I'm up to. It's purely for my own benefit, though should anyone other than myself and my mum read it then all the better. However as most of my friends are people from college or work colleagues, many of whom are far smarter than me and more knowledgeable about this stuff, I expect they'll only read it for the schadenfreude gleaned from my inability to perform simple tasks such as setting up SSH (must be the firewall, or I'll have to get out Wireshark).

So what have I got planned? Well, I've seen enough hardware bringups to be painfully aware that it's best to walk before I try running - let me just get the bleedin' thing plugged in and booting reliably first. Then I can try a few simple projects, maybe a Squeezebox type thing? After that I've got my eye on those GPIOs, and I'm wondering what I can wire up to them. One of my favourite toys when I were a nipper was BigTrak and I was thinking of making a programmable robot type thing, maybe add a camera, a few sensors, battery pack or really long power cable, etc., then it's all "just" software. There are lots of pre-made robot parts which I could use, the question is how much I want to make myself? Maybe I should just buy a BigTrak, chuck out the microcontroller and use the chassis?

Fifty-Nine Icosahedra screensaver (in windowed mode
for screenshot) - looks better when moving, but still
not good

As for other geek projects - they're currently languishing, damning reminders of the fact that I'm not a completer/finisher. I've been trying to get some C++ practise in an environment where I'm not afraid of breaking stuff (i.e. not work) and I've wanted to do some 3-D projects since I wrote a crude 3-D engine in college. One project is an animation tool which will do inverse kinematics, but after initial success in rendering meshes and skinning them with DirectX (and that was a mission and a half, I tells ya) I decided to switch to OpenGL and got bogged down in the code which loads in resources and follows references to more resources. So that's on permanent hold until I can be bothered with it again. I also wrote a screensaver which renders the Fifty-Nine Icosahedra. The hardest bit was recalling enough GCSE-grade trig to sort out the geometry, but once I got there it gasped into life and... it was a bit disappointing really. Though there are some really weird shapes, on the whole they're a bit samey. It really needs someone with a girlier eye to pick a decent colour scheme, or maybe it'd be better with a single colour, some light sourcing and anti-aliasing, and it could do with some funky transitions between the shapes. Also I tried it at work where it really doesn't agree with my dual monitors, though I'm told that's a problem with many screensavers. I might resume work on that once I get over my disappointment. I wonder if it'd work with the RPi's OpenGL ES? It already works under  Windows or Linux, might need some minor mods to the XWindows code

So that feature-length pilot was a small taste of the hi jinks to come. With luck my Raspberry Pi will arrive soon and the next instalment will be all about how easy it was to set up. Or have close-ups of the voltage regulator with a neat white hole burnt through it.