Category Archives: Projects

The Euroquadruped, or the solution to wall wart Tetris

Having relocated from the UK to Poland, the change in mains plugs has never quite been resolved. All the equipment that came from the UK has 13A plugs on it, and all the local sockets are the CEE 7/5 type. Then there are locally-acquired bits and pieces  which generally have two-pin Europlugs. No matter how many adapter cables and extension leads I make, or change the plug or socket on, there’s always something that doesn’t fit, or won’t reach the nearest compatible socket.

Of particular annoyance are various chargers and wall warts. They’re all bigger than a standard Europlug, and there’s no standard for which way the ‘lump’ of the charger will be attached, so connecting several of them in to a multi-socket extension lead doesn’t work well. Often one charger will obscure one or more sockets in such a way that all the things you need just won’t fit, or the whole assembly becomes so big and unwieldy that things start falling out under their own weight.

It is therefore with some relief that I announce the debut of the Euroquadraped: one 13A plug with short cables to four Europlug sockets. It reminded me of an octopus but only has four ‘legs’, hence the name.

IMG_20180211_221335.jpg

Getting all four cables in to the 13A plug was a bit fiddly, but choosing a roomy plug helped. The little Europlug sockets are neat. I’ve only seen them here in Poland. The finger ring to discourage pulling on the cable is a nice touch, and doubles as a cord grip internally. They even (finally) have safety shutters on the socket holes, roughly 60 years after shutters became standard on the British 13A socket…

The great advantage of this thing is that each socket is independent of the others and can find its own equilibrium with whatever electrical carbuncle is plugged in to it.

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It’s trivially simple, but it’s going to save a lot of frustration in the workshop.

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Garage door opener life extension

This little thing is really annoying. It’s the remote control for our electric garage door, and I use it several times a day to get my bike in and out. Luxury, pure luxury. Or it would be, if it worked properly. The trouble is that about half the time after pressing the button, it locks up, stuck either on, with its little red LED lit, or off, so it won’t open or close the door, and drains the battery. The only way to fix it is to pull it apart, take out the battery, and put it back in without losing any of the bits of plastic. You can imagine how much fun that is with gloves on, in the rain, when you’re in a hurry. Yeah, yeah, first world problems, I know. But there doesn’t seem to be any way of opening our garage door manually, which is a nuisance.

IMG_20171215_155448.jpg

Inside is a little PCB containing a PIC12F635 microcontroller and a simple 433MHz transmitter circuit using a couple of transistors and a resonator. I did all the obvious things: replace the battery, clean the board with solvent, all of that. Nothing helped. It seems there’s a bug in the PIC’s software which makes it prone to locking up. The switch under the button is rather worn and thus suffers from contact bounce, and I think that’s what’s upsetting it.

I tried filtering the signal from the button to the PIC with an RC network. That didn’t help: the PIC didn’t even respond to the button any more. Presumably it needs a fairly quick risetime to trigger an interrupt, or something similar.

There is a second button which is less worn. It transmits a different code which doesn’t seem to do anything on our garage door, but it never crashes the PIC. I considered swapping the switches over, but they’re surface-mount and glued down, and the chances of removing both of them and successfully soldering them down again undamaged were slim.

I wondered about rewiring the PCB so that the input to the PIC is always active, and the button just switches the power to the PIC. A quick test by adding a blob of solder and removing and reconnecting the battery showed that wasn’t going to work: the PIC just didn’t transmit. It needed to have the power applied and then have the button activated.

There was another issue to address. The button, when it worked, was prone to getting pressed by accident as the bunch of keys rattled around in my pocket. That led to the garage door opening itself at odd times, which wasn’t great for the security of our bikes. Somehow modifying it to be less prone to accidental operation would be nice. 

Design changes were called for. Since the second button is redundant, I decided to convert it in to a power switch, so it has to be held down while the real button is pressed, and releasing it will guarantee that the power is cut from the PIC so it can’t remain locked up. I cut the power track to the PIC and took advantage of the PCB layout to add a P-channel MOSFET in series with it, then cut the track from the second button to the PIC’s input and wired it to the MOSFET’s gate. The buttons both have one terminal to battery negative. A pullup resistor between gate and source completes the circuit.

IMG_20171215_155001.jpg

Here’s the modified board. You can see the remnants of some of my previous repair attempts, and the extra MOSFET and pullup resistor at top right. Now, to open or shut the door, I have to hold down the button on the right and press the left button, rather like using a shift key on a keyboard.

It seems to work reliably now, so leaving the house and returning are considerably quicker and less stressful. 

Incidentally, I did the repairs and modifications in the office, which is several miles away from the offending garage door. To check that the remote was actually transmitting properly, I used my Tektronix 7912AD programmable digitizer with 7A29 vertical plugin. Originally intended for high-speed laser and nuclear physics research, it’s kind of overkill for testing a garage door opener, but its 700MHz bandwidth is plenty fast enough to get a clear picture of the transmission using just a loop of wire connected to the input. Analogue technology at its very finest. Here’s its TV output connected to a little LCD monitor showing the 433MHz signal from the remote.

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Cracking a password-protected PDF file

Suppose you asked an insurance company for a letter. The insurance company kindly sent it as a PDF attached to an email. Sensibly, they protected that PDF with a password which they told you over the phone. You wrote it in a notebook and then left the notebook at work over the weekend.

pdf-password

How could you read the letter in the password-protected file at home, then? Remembering that the password was definitely an English word, and all in lower case, a dictionary attack has got to be worth a try.

Linux provides some handy tools for this. There’s a list of English words in /usr/share/dict/words, and a suite of PDF tools which can attempt to open the file using a password, indicating success or failure. A few minutes with Python and:

#!/usr/bin/python
import os,sys

wf=open('/usr/share/dict/words','r')
while True:
  word = wf.readline().strip().lower()
  if word == '':
    print "No solution found"
    break
  print word
  cmdline = 'pdftotext -upw "'+word+'" '+sys.argv[1]
  result = os.system(cmdline)
  if result == 0:
    break

The same thing must be possible in a more hipsterly fashion using awk, but I couldn’t be bothered to figure out a sufficiently baroque command line.

By the way, the password was ‘orange’. Don’t tell anybody.

Systemd for Embedded Linux

Over the last few years, there has been a lot of controversy in the Linux world about systemd. As I understand it, systemd is intended to be a better-engineered, more powerful version of the motley collection of little programs and scripts which keeps the essential services on a Linux system running.

systemctl

The controversy arises because the original 1970s Unix way of doing things was to rely on a motley collection of little programs and scripts for everything, each of which was simple but well understood, and to knit them together to form a complete operating system. Systemd takes a different approach, using larger and more sophisticated components which are more dedicated to particular tasks, such as managing services or network connections. This is supposed to make it more efficient and easier to manage in the twenty-first century.

I’ve been doing some work recently on an embedded Linux system which runs on the latest version of Debian Linux, version 8 (‘Jessie’). Debian Jessie fully supports systemd to the extent that it seems to be the default way of doing things. I thought I’d experiment with it a bit.

When working on an embedded Linux system, I very frequently want to have a piece of my software run reliably at startup, get restarted if it fails, and be able to output logging information to an easily-managed place. In this case, my software provides a D-Bus interface to a piece of industrial electronics.

In the past I’ve relied on copying and pasting scripts from other pieces of software, and managing log files has always been a bit of a mess. It’s hard to do these things right, so re-inventing the wheel is too risky, which means that the best strategy is to copy somebody else’s scripts. I have never counted the hours of my time which have been wasted by dealing with awkward corner cases and peculiar bugs due to recycled scripts behaving in ways I hadn’t anticipated.

What does it look like with systemd? There are some helpful tutorials out there, including this one from Alexander Patrakov, so it didn’t take me too long to put together a service file which looks like this:

[Unit]
Description=My D-Bus Gateway
[Service]
Type=dbus
BusName=com.martin-jones.gateway
ExecStart=/usr/bin/my_dbus_gateway
Restart=always
[Install]
WantedBy=multi-user.target

I’ve changed the names to protect the innocent, but the contents of the file are pretty self-explanatory. The [Unit] section just includes a description which is readable to a human being. The [Service] section describes the service itself. In this case it’s of type  dbus, which means that systemd will check that the service name (com.martin-jones.gateway in this case) gets correctly published on to D-Bus. The Restart=always setting means that my software gets restarted if it exits. The [Install] section just indicates that this service should run when the system comes up in multi-user mode (like the old runlevel 5).

Having created this file, I simply copied it into /etc/systemd/system/my_dbus_gateway.service and, lo and behold, my new service worked. It was immediately possible to manage the service using commands like

systemctl start my_dbus_gateway.service
systemctl stop my_dbus_gateway.service
systemctl status my_dbus_gateway.service

Great! That’s exactly what I wanted.

Now for logging. I’d heard that systemd would log the stdout and stderr outputs of services into its own journal, and forward that to syslog as required. It does, but there’s a subtlety. Output from stderr appears in /var/log/syslog immediately line-by-line, but output from stdout gets aggressively buffered. This means that it gives the appearance of not working at all unless you explicitly flush the stdout buffer in your code using something like

fflush(stdout)

That’s the only wrinkle I came across, though.

In summary, using systemd’s facilities has made my life as an embedded Linux developer much, much easier and hopefully more reliable. That’s a good thing. My top tips for getting your software working under systemd are these:

  • Create your .service file using the recipe above and the documentation
  • Don’t forget to flush stdout if you want to see it in syslog.

Lattice FPGA programming adapter from the junk box

Working with Lattice FPGAs recently, I had a need to program one but couldn’t find my ‘proper’ (Chinese clone, bought from eBay) programming adapter. When I started the Diamond Programmer software, though, it claimed it could see a USB programming adapter. It turned out that I’d left an FTDI ‘FT2232H Mini Module‘ attached to the PC. I use the module for all sorts of little debugging exercises: most often as a dual serial port for serial port debugging, but it also works for programming Parallax Propeller microcontrollers.

Img_0603

As luck would have it, the Diamond software recognises the unadulterated FT2232H as a legitimate USB programmer, and pressing the ‘Detect Cable’ button finds it. Note that if you plug in a new USB device, the Diamond Programmer software needs restarting before it can see it.

The FT2232H has two ports, A and B, and these appear as ports FTUSB-0 and FTUSB-1 in the Diamond software. All that remained was to figure out the wiring. Fortunately, there are a lot of clues in the schematics of various Lattice evaluation boards, particularly the MachXO2 Pico Board and the iCE40 Ultra Breakout Board.

diamond-programmer

Here’s the wiring, both for SPI and JTAG, referred to the pins on the Mini Module. I chose to use port B since it was more convenient for my prototype board. Translating the wiring to port A is left as an exercise for the reader.

SPI    JTAG  FT2232H  Mini Module
SO     TDI   DBUS1    CN3-25
SI     TDO   DBUS2    CN3-24
SCK    TCK   DBUS0    CN3-26
SS_B   ISPEN DBUS4    CN3-21
CRESET TRST  DBUS7    CN3-18
GND    GND   GND      CN3-2,4

It works well, and does exactly what it should.

First steps with a Lattice iCE40 FPGA

I’ve just been doing some work with the iCE40 series of FPGAs from Lattice Semiconductor. They’re small FPGAs, with up to 7680 gates, and they’re very low-power, which is nice for mobile applications. From what I can gather, Lattice acquired the designs when they bought a company called SiliconBlue in 2011. I’ve been used to using the Lattice Diamond software with their other chips, but the iCE40 chips aren’t supported by Diamond. Instead, they get their own software called iCEcube2. It’s a bit of a pain to use and not very well documented. I’ve just been through the process of starting a project and getting a very basic design working, and I’m writing about it here in case someone else finds it useful.

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The iCEcube2 software looks convincingly like an IDE, but it isn’t, really. It doesn’t even seem to have a way of creating new source code files, and the order in which some things have to be done is not at all obvious. I think iCEcube2 is really designed for taking existing designs and implementing them on the Lattice iCE40 chips. While the software is a complete dog’s breakfast, it does have the key advantage of being free. You do need to create a node-locked licence for it using their licencing page.

iCEcube-blank

To start an empty project, double click Project -> New Project. Select the chip you’re going to use. This creates a folder with the title of the project, containing:

  • <project>_sbt.project
  • <project>_syn.prj
  • folder <project>_Implmnt, containing folder sbt, containing folders constraint, log and outputs. All are empty apart from iceCube0.log in log folder.

Now you can add your source files. If you click on ‘Synthesis Tool’, then an ‘Add Synthesis Files’ menu item appears, but clicking on this doesn’t do anything useful. You have to right-click on ‘Add Synthesis Files’ and select ‘Add Files…’ from the pop-up menu. Go figure. I used a very simple VHDL source file:

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;

ENTITY test IS
 PORT
 (
 d: in std_logic;
 q: out std_logic;
 qn: out std_logic
 );
END test;

ARCHITECTURE rtl OF test IS
BEGIN

 q <= d;
 qn <= not d;
 
END rtl;

At this point I’d expect to be able to allocate signal names (d, q and qn, in this case) to pins on the device package. But you can’t do that yet in the wonderful world of iCEcube2. All the buttons on the toolbar are greyed out. The way to proceed is to double click ‘Run Synplify Pro Synthesis’. Hopefully your code will compile without errors, and lots of files get created.

The project folder now contains:

  • stdout.log and stdout.log.bak
  • synlog.tcl
  • loads of stuff under <project>_Implmnt

Two new files appear in the project under ‘P&R Flow’: <project>.edf and <project>.scf.

Now double-click ‘Run P&R’. The design will get placed and routed, and a bitmap gets generated for programming the chip.

At this point the toolbar buttons for timing constraints, pin constraints, floor planner, package view, power estimator and timing analysis become active. Hurrah! Now you can change your pin constraints.

iCEcube-toolbar-enabled

Click on ‘Pin Constraints Editor’, the fourth icon from the left. Put in the pin locations for the signals you want. Make sure you click the ‘locked’ checkboxes on the left hand side, otherwise the place and route process is likely to move them. Press ctrl-S to save. The constraints get saved in <project>_Implmnt\sbt\constraint\<top design file>_pcf_sbt.pcf. You will then get asked to add the file to the project. Say yes.

If you’re using source control, it’s a good idea to add this file to it. I’m not so sure about all the other junk that iCEcube generates.

Now double-click ‘Run P&R’ again and the new bitmap file will be generated, using your pin constraints.

Programming an actual chip (or at least its SPI Flash ROM) needs the Diamond Programming tool, which comes as part of the Lattice Diamond software and *not* as part of iCEcube2. That’s just another couple of gigabytes to download, and another licence (free) to acquire, so it’s a pain, but it does work.

Orange Internet and port forwarding, continued

A long time ago, I wrote an article about how I worked around the lack of NAT loopback support on the Orange LiveBox broadband router. At the time, it was a pain to get everything working right. Having just moved house, we made the sensible decision to stay with the same broadband provider, in order to avoid having to re-invent or at least re-configure all this stuff.

Well, it turned out not to be as easy as that. Nothing ever is, it seems. The new Orange broadband service comes with a ‘FunBox‘ instead of a ‘LiveBox’. Fun? Who said? Not in my experience. The web interface to the box looks comfortingly similar to the old LiveBox, so I thought it would work the same way. No chance.

funbox2

What’s the problem I’m trying to solve here? Well, I have a little SheevaPlug which hosts some services I need to use from various locations when I’m working. Yes, I know I should put those services ‘in the cloud’, but that would involve both paying money and solving a whole load of other problems. For years and years, I’ve simply had a port forwarding rule set up on my home broadband router so that the SheevaPlug is accessible from the internet. A little touch of dynamic DNS courtesy of dyn.com and it’s all worked fine.

Fast forward to 2015. I tried to recreate the setup I’d always used, but with the FunBox (hah!). The old setup went like this:

home_net_old

  • the broadband router just does the usual NAT routing and behaves as a dumb wi-fi access point. It has a port forwarding rule set up to forward port 22 (ssh) to the SheevaPlug
  • the SheevaPlug hosts my ssh server, and provides the DHCP and DNS services to everything on the network, so I get proper local hostname lookups, easy-to-manage IP addresses, and can solve the NAT loopback problem.

That’s it. I tried to set up the FunBox the same way. What could possibly go wrong?

I boldly switched off the DHCP and DNS servers in the FunBox and switched over to using the ones on my SheevaPlug. Everything seemed to work fine, except…the TV. Yes, the TV decoder is connected to the FunBox via Ethernet, so the whole shebang comes down the wire. No aerial required. Trouble is, the FunBox seems to need to set up the TV decoder by DHCP otherwise it doesn’t know it’s there, so you get no telly. Oh well, I’ll use the DHCP server in the FunBox and put up with the inconvenience.

Even that doesn’t work out. In order to solve the NAT loopback problem, which the miserable FunBox suffers from just like the LiveBox, I need to run my local DNS server. Except that the brain-dead FunBox won’t let you change the DNS settings on its built-in DHCP server. How annoying is that?

OK, accept that NAT loopback will remain a problem. Maybe I’ll find another way round that. Now for the showstopper: the blessed FunBox refuses to forward port 22. It will forward every other port under the sun, but not 22. The web configuration interface just won’t accept the setting: it ignores it. Doesn’t even give an error message. You’re just not having it. Oh well, maybe I have to expose my ssh server on a different port and put up with changing all the gazillion clients which know about it. Except I’ve still got the loopback problem. This is getting unpleasant.

Before tearing out what little remained of my hair by this point, I slept on the problem and had a brainwave. The FunBox supports a ‘DMZ’ feature, in which it’ll forward all incoming internet traffic to a particular IP address on the LAN. I tried it, experimentally sending all internet traffic to the poor, naked SheevaPlug, and it worked! At last, sweet relief: something which does what it says on the tin.

Clearly exposing the server in all its complacent insecurity to the internet isn’t a good idea. I needed to put a firewall in the way. A rummage in the cupboard produced a spare Raspberry Pi and a USB to Ethernet adapter. I programmed OpenWRT on to an SD card and booted up. It turned out to be easier to configure it through the command line than with the web interface, LuCI, which isn’t exactly finished yet. Some fiddling later and I’d managed to disable its DHCP and DNS features and enable incoming connections only on port 22.

Adding the firewall had another bonus: it meant I could re-enable my DNS and DHCP servers and let them look after the LAN without the wretched FunBox knowing anything about it. It just has to live a simple life, looking after the telly and the firewall. I disabled its built-in Wi-fi access point and added an ageing Linksys WAP54G running DD-WRT software after the firewall. Lovely.

home_net_new

There is one fly in the ointment: the Raspberry Pi turns out to make a rubbish router. Our 30 megabit internet connection is reduced to 3 megabits on its way through the Pi. I don’t know if it’s something to do with my configuration, or the release of OpenWRT (15.05-rc3) I’m using. When I’ve unpacked enough boxes to find another router, I’ll try that.