Why so serious?

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"The most dangerous tradition we hold about work is that it must be serious and meaningless. We believe we are paid money to compensate us for work not worthwhile on its own.". --Scott Berkum "The Year Without Pants"


Twisted Blades' BeagleBlox System on Module

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Many years ago I started using Cadsoft Eagle  to design printed circuit boards.  REVOLT's various lithium ion battery management systems were all designed and built using Eagle.  A licensed copy is about $1200, and upgrades have been pretty reasonable.  

My latest project, started a few months ago is to design an ARM processor based System on Module (SoM).  These are common in the industry, since the difficult high speed, multilayer board can be designed by an expert.  The customer designer just has to design and layout the less dense, easier low speed peripheral interfaces.  The problem with these is they are packaged into lay down modules, where the module is parallel or nearly parallel to the board.  If you want to put a bunch of these into a small area you waste a lot of board space under those modules.

I've decided to take the BeagleBone Black's open design and move it into a module that can be more easily integrated into my projects.  Specifically I want to build a board that plugs into the backplane at right angles to allow a bunch of these in a small amount of space.  

The Beaglebone Black is a small hacker friendly ARM board that uses TI's AM335x line of processors.  1Ghz, 512MB RAM and 10/100 or 1GB ethernet for about $45.  About the same processing power as a two year old cell phone, and only using a few watts of power.

I want a bunch of them in a server rack as small nodes in a hosting or compute cluster.  My idea is to repackage the BeagleBone Black into a DIMM module style board.  DIMM memory module connectors are dense (200+pins), cheap, and require only the backplane side connector.  The module side connector is just a card edge.
168.gif
If you've ever looked at a computer motherboard these modules are often placed very close to each other.  My design will be able to house several hundred processors in 1 or 2U rack units.  This is almost unheard of density, and is an area being actively pursued by HP, Google and a few other vendors.  My design will be a little simpler, hopefully a lot cheaper, and more accessible.  

To get there I need to do my first 4 or 6 layer PCB, with higher speed signals and a 324 pin BGA package.  This is turning out to be a lot more complex than I expected.  I've been at it for a few weeks and Eagle just isn't working out great.  

Below you can see I've escape routed most of the BGA package on the right.  I'm trying to figure out a clean way to route all of the traces to the 4GB DDR3 memory module on the left.  The data lines at the bottom went OK though their lengths differ more than I want.  The address lines at the top are more complex, and have been trouble.  Eagle's has a tool for measuring the lengths of signals, but it doesn't have a tool for making a group of more than two signals the same length. 
EagleDDRrouting.png
So while I can't afford the cost, and I really don't want to learn a new app, I'm going to try Altium.  Well see how that goes in a future post.



IRC notification Bot using Ruby Cinch

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My RFID door controller written in Bash has been going for a month now, and has proven to be reasonably stable.  I wanted to add some kind of notification that people were entering/leaving the Maker space.  Since a portion of the group hangs out in the freenode IRC channel #grmakers I figured I'd hack up a quick command line to IRC bot.  This is common in the Java world for use with various continuous integration (CI) systems.  Both Logstash and irccat exist.  I don't have Java installed on the door controller, and doing so seemed like a bit of a hassle.  I do have Ruby, and Ruby has a very nice IRC bot builder gem called Cinch.

Cinch is primarily designed to be a bot, and respond to messagaes directed at it on the IRC channel.  With a lot of searching I got something working.  This script should be started up from daemontools or init.  It listens on a TCP port, and gates any text pasted into the TCP socket through to the IRC channel.  Note that this has no authentication or data validation, so only use this bound to localhost on a dedicated machine.


require 'socket'
require 'cinch'

MY_CHANNEL = "#door-bots"
MY_LISTENING_PORT = 2000

class MonitorBot
  include Cinch::Plugin

  listen_to :monitor_msg, :method => :send_msg

  def send_msg(m, msg)
     Channel(MY_CHANNEL).send "#{msg}"
  end

end

bot = Cinch::Bot.new do
  configure do |c|
    c.nick            = "door"
    c.realname        = "Door Bot"
    c.user            = "myuser"
    c.server          = "irc.freenode.org"
    #c.port            = 7000
    #c.ssl             = true
    c.channels        = [MY_CHANNEL]
    c.verbose         = false
    c.plugins.plugins = [MonitorBot]
  end
end

def server(bot)
  print "Thread Start\n"
  server = TCPServer.new '127.0.0.1', MY_LISTENING_PORT
  loop do
    Thread.start(server.accept) do |client|
      message = client.gets
      bot.handlers.dispatch(:monitor_msg, nil, message)
      client.puts "Ok\n"
      client.close
    end #Thread.Start
  end #loop
end

Thread.new { server(bot) }
bot.start

Sending text to the channel is easiest to do using Netcat:
echo "Hello from the command line" | nc localhost 2000
Some GRMakers members pointed out existing solutions that I missed that would have been far easier to implement. Eric Raymond wrote irker which works similarly to the above but is more full featured and accepts commands as JSON. Even better suited to command-line scripting is "ii" which creates a virtual filesystem with input and output pipes created dynamically for each joined channel.  

Simple Door Access in bash

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RFID Door Access controller using Raspberry Pi, AdaFruit PN532 RFID reader, and Wiring Pi and implemented as 29 lines of bash.  GPIO 17 (0 in WiringPi) is used to activate the door release and libnfc provides the nfc-poll command that scans for a card.

(Edited Nov 2. I was reminded that the backtick (`) has been deprecated for the more POSIX friendly $() operator. Fixed but not tested.) 
 
#!/bin/bash

FILENAME='/home/pi/door_basher/allowed_tags.txt'
LOGNAME='/home/pi/door_basher/access_log.txt'

gpio mode 0 out
gpio write 0 0


while true; do 
   TIMESTAMP=`date`
   NFC=$(nfc-poll 2>&1 |grep "UID")

   if [ $? -eq 0 ] ; then
       CARDID=$(echo $NFC|cut -f2 -d ":"|sed  -e 's/[ \t]//g')
       NAME=$(egrep "^$CARDID" $FILENAME) 
       if [ $? -eq 0 ] ; then
          NAME=$(egrep "^$CARDID" $FILENAME|awk -F $'\t' '{ print $2;}') 
          echo "$TIMESTAMP ALLOW $NAME ($CARDID)" | tee -a $LOGNAME 
          gpio write 0 1
          sleep 10
          gpio write 0 0
       else 
          echo "$TIMESTAMP DENIED $NAME ($CARDID)" | tee -a $LOGNAME
          sleep 2
       fi
    fi
done

The allowed_tags.txt file is a tab delimited list of the MiFare card UIDs and the username. For centralized management use a cron job to update this file from a central webpage and to upload the access log.
7e33456e      Mark Farver
763a45df       User Two
It may be wise to start this with init or damontools, so it will always be running. It could probably use some more testing and thought. It does not do a very good job of guaranteeing the door will be re-locked if the script crashes or is aborted.

Custom GrrCON conference badge

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Finished the admission badges for the GrrCON hacking convention here in Grand Rapids.  I modified the basic Arduino Uno design, converting it to run off a battery, adding a LED signboard, and putting it on a custom PCB that matches the conference logo.  

To keep costs low I ran the processor and LEDs direct from the battery. This was a mistake.  I should have used a boost regulator, the conference chose white and purple LEDs for some of the badges.  These need much higher forward voltages (2.5 and 2.7V, respectively).   Without a boost regulator the battery life is quite short, as it drops below the LED voltage pretty quickly.  Future version will use something like the Microchip MCP1623 to boost the voltage and keep it steady as the battery discharges. 

USB video playback on Sony Bravia TVs

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I was trying to play a video from a USB stick on a Sony Bravia TV KDL-55EX500.  

The TV is a little picky about the video format.  I spent a few minutes figuring out what combination of resolution and video settings were needed to get full screen playback.  The TV seems to like MPEG-2 video and 1920x1088 resolution. The command-line for Linux's avconv command was this:

 
avconv -i input.mpg -f mpeg -target ntsc-dvd  -s 1920x1088 output.mpg

I also wanted to turn off the annoying "Bong" noise the TV makes in startup but couldn't find it anywhere in the settings menu. Turns out Sony added that option back in later firmware. If you upgrade the TVs firmware to the latest version you can turn it off.

Juniper JunOS USB partition table rescan

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As an update to my upgrading Juniper EX switches from USB.  Upgrading from a USB thumb drive works well, but if you don't have one handy you might try to use another "dual use" mass storage device like a phone or Kindle.  Problem is the delay while that device initializes causes JunOS to fail to read the partition table.  You will have a /dev/da1 entry, but no /dev/da1s1:

umass1: Amazon Amazon Kindle, rev 2.00/1.00, addr 3
da1 at umass-sim1 bus 1 target 0 lun 0
da1:  Removable Direct Access SCSI-2 device
da1: 40.000MB/s transfers
da1: Attempt to query device size failed: NOT READY, Medium not present
(da1:umass-sim1:1:0:0): READ CAPACITY. CDB: 25 0 0 0 0 0 0 0 0 0
(da1:umass-sim1:1:0:0): CAM Status: SCSI Status Error
(da1:umass-sim1:1:0:0): SCSI Status: Check Condition
(da1:umass-sim1:1:0:0): UNIT ATTENTION asc:28,0
(da1:umass-sim1:1:0:0): Not ready to ready change, medium may have changed
(da1:umass-sim1:1:0:0): Retrying Command (per Sense Data)
The workaround seems to be to issue a "camcontrol rescan da1" to rescan the parition table.

This issue only shows up on some versions of Junos, and the camcontrol command is also only available on some versions of Junos. 
I found a new trick in iptables I wasn't aware of.  Turns out iptables tracks all connections, even ones that are not going to be NAT'd.  On a busy webserver or router this means iptables is wasting resources tracking connections when it should be just routing.

The raw table in iptables can be used to set a NOTRACK flag on a packet, and that packet will not traverse the ip_conntrack stuff.

So for a busy webserver, you could disable tracking for web connection states:
iptables -t raw -A PREROUTING -d <server IP> -p tcp --dport 80 -j NOTRACK
iptables -t raw -A PREROUTING -s <server IP> -p tcp --sport 80 -j NOTRACK

Or on a machine that is routing between several internal networks and also NATing external connections you could disable tracking for the internal to internal stuff.
iptables -t raw -A PREROUTING -s 172.16.0.0/16 -d 172.16.0.0/16 -j NOTRACK

On one of our core Linux routers the number of ip_conntrack entries dropped from an average of 65-70k down to about 2k. 

Upgrading Juniper EX series switches from USB.

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This is for my notes. Generally I use this to upgrade the firmware of an EX4200 switch to the same JunOS version as the rest of a virtual chassis, BEFORE connecting the VC cables.  I'm doing this from memory, so if there are any mistakes let me know.

You will need to have access to a shell. The "root" user logs into shell automatically, other users should run "start shell"

From the shell run these commands:

 # mkdir /mnt/usb

Insert the USB stick (FAT32 formatted) into the port at the back of the switch. It should have the firmware on it, generally in a file named something like "jinstall-ex-10.3R3.4-domestic-signed.tgz"

 # mount -t msdosfs /dev/da1s1 /mnt/usb"

Note that tab completion works on Junos, to save some typing just enter the frist few characters of the filename and hit "tab"

 # cp /mnt/usb/jinstall-ex-10.3R3.4-domestic-signed.tgz /var/tmp 

If the switch is running firmware older than 10.3 you should upgrade the loader too:

 # cp /mnt/usb/jloader-ex-3242-11.3I20110326_0802_hmerge-signed.tgz /var/tmp
 # umount /mnt/usb
 # cli
At the ">" cli prompt: If the firmware on the switch is older than 10.3 you will need to install the updated jloader
 > request system software add /var/tmp/jloader-ex-3242-11.3I20110326_0802_hmerge-signed.tgz
then:
 > request system software add /var/tmp/jinstall-ex-10.3R3.4-domestic-signed.tgz reboot

Dual IP stack for twice the love

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Several weeks too late for world IPV6 day: My first directly connected dual stack router (no tunnel). In this case a Juniper MX-80 connected to TW Telecom.
mfarver@RTR2> ping 2001:470:1f0e:d23::1
16 bytes from 2001:470:1f0e:d23::1, icmp_seq=0 hlim=62 time=46.032 ms
16 bytes from 2001:470:1f0e:d23::1, icmp_seq=1 hlim=62 time=45.363 ms
16 bytes from 2001:470:1f0e:d23::1, icmp_seq=2 hlim=62 time=44.284 ms

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