Just Enough Developed Infrastructure

Patching Ruby USB on Mac OSX

When my son got himself Buzz Quiz, it struck me that there was no way to create your own quiz. So that got me started on reading up on how I could use the Buzz Quiz controllers on my Mac.

Selecting a toolkit

All effort has gone to libusb. But i did not want to into C code again. This links sums up a list of related wrappers or bindings: http://mcuee.blogspot.com/2009/05/libusb-related-wrappers-or-bindings.html

I've considered the following options:

Installing libUSB (using macports)

ruby-usb requires you to have libusb http://www.libusb.org/ . This library has a current version of 1.0.3 , this version version not compatible with ruby-usb. Luckily macports still has the older versions available for us. The version we need is the libusb-compat . Note: that my macports where installed in /opt/local so you might need to change some paths.

Lets list the versions available by macports:

$ sudo /opt/local/bin/port list |grep -i usb
usbprog                        @0.1.8          cross/usbprog
libusb                         @1.0.3          devel/libusb
libusb-compat                  @0.1.3          devel/libusb-compat
libusb-legacy                  @0.1.12         devel/libusb-legacy

We install the libusb-compat version:

$ sudo /opt/local/bin/port install  libusb-compat
 --->  Computing dependencies for libusb-compat
 --->  Fetching libusb
 --->  Verifying checksum(s) for libusb
 --->  Extracting libusb
 --->  Applying patches to libusb
 --->  Configuring libusb
 --->  Building libusb
 --->  Staging libusb into destroot
 --->  Installing libusb @1.0.3_0
 --->  Activating libusb @1.0.3_0
 --->  Cleaning libusb
 --->  Fetching libusb-compat
 --->  Attempting to fetch libusb-compat-0.1.3.tar.bz2 from http://mesh.dl.sourceforge.net/libusb
 --->  Verifying checksum(s) for libusb-compat
 --->  Extracting libusb-compat
 --->  Configuring libusb-compat
 --->  Building libusb-compat
 --->  Staging libusb-compat into destroot
 --->  Installing libusb-compat @0.1.3_0
 --->  Activating libusb-compat @0.1.3_0
 --->  Cleaning libusb-compat

Getting ruby-usb

The most recent success with lib-usb I found was described on http://markmail.org/message/peidli3qjrqpwbk5

downloaded the latest cvs snapshot from http://www.a-k-r.org/ruby-usb/ . This will install version 0.2-something. The rubygems is only the version 0.1 version. There were some bug fixes since then.

$ svn co svn://svn@svn.a-k-r.org/akr/ruby-usb/trunk ruby-usb
$ cd ruby-usb

Solving the library and include paths

replace the extconf.rb as follows where /opt/local is the place where you installed libusb

require 'mkmf' 
find_header("usb.h", "/opt/local/include") 
find_library("usb", nil, "/opt/local/lib") 
have_library("usb", "usb_init") 

Specify the correct build architecture

For some reason, the make mkmf decides to put both the ppc and the i386 as flags to the architecture. So we have to specify the i386 using the ARCHFLAGS variable:

$ ARCHFLAGS="-arch i386" ruby extconf.rb
checking for #include <usb.h>
... yes
checking for main() in -lusb... yes
checking for usb_init() in -lusb... yes
creating Makefile

Not specifying the architecture would result in a warning at compile time (file is not of required architecture)

gcc -I. -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin9.0 -I. -I/opt/local/include  -fno-common -arch ppc -arch i386 -Os -pipe -fno-common  -c usb.c
cc -arch ppc -arch i386 -pipe -bundle -undefined dynamic_lookup -o usb.bundle usb.o -L. -L/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib -L/opt/local/lib -L. -arch ppc -arch i386    -lruby -lusb  -lpthread -ldl -lm  
ld warning: in /opt/local/lib/libusb.dylib, file is not of required architecture

At runtime this would result in an error

dyld: lazy symbol binding failed: Symbol not found: _usb_init
  Referenced from: /Library/Ruby/Site/1.8/universal-darwin9.0/usb.bundle
  Expected in: dynamic lookup

dyld: Symbol not found: _usb_init
  Referenced from: /Library/Ruby/Site/1.8/universal-darwin9.0/usb.bundle
  Expected in: dynamic lookup
Trace/BPT trap

Even though we have the usb_init compiled in the dynamic library

nm /opt/local/lib/libusb.dylib |grep -i usb_init
         U _libusb_init
00001630 T _usb_init

The reason we only get an error at runtime is that ruby-usb dynamically load the library. In our case it will load the libusb.dylib which points to version 0.1.4 of the libusb.

$ ls -l /opt/local/lib/libusb.dylib 
lrwxr-xr-x  1 root  admin  18 Sep 29 09:24 /opt/local/lib/libusb.dylib -> libusb-0.1.4.dylib

Also check if old libraries exist in other places

$ ls -l /usr/lib/libusb.dylib 
-rwxr-xr-x  1 root  wheel  24084 Sep 29 10:46 /usr/lib/libusb.dylib
$ sudo rm /usr/lib/libusb.dylib

Build the library with make

$ make
gcc -I. -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin9.0 -I. -I/opt/local/include  -fno-common -arch i386 -Os -pipe -fno-common  -c usb.c
cc -arch i386 -pipe -bundle -undefined dynamic_lookup -o usb.bundle usb.o -L. -L/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib -L/opt/local/lib -L. -arch i386    -lruby -lusb -lusb  -lpthread -ldl -lm

Patching the usb.rb

The last thing to get it working is to have usb.rb catch the error Errno::ERANGE . We do this by adding it to the corresponding line in usb.rb

<       rescue Errno::EPIPE, Errno::EFBIG, Errno::EPERM,Errno::ERANGE

>       rescue Errno::EPIPE, Errno::EFBIG, Errno::EPERM

If we don't patch it , it would result in the following error:

[Errno::ERANGE: Result too large - usb_get_string_simple
    from /Library/Ruby/Site/1.8/usb.rb:412:in 'usb_get_string_simple'
    from /Library/Ruby/Site/1.8/usb.rb:412:in 'get_string_simple'
    from /Library/Ruby/Site/1.8/usb.rb:349:in 'description'
    from /Library/Ruby/Site/1.8/usb.rb:276:in 'open'
    from /Library/Ruby/Site/1.8/usb.rb:349:in 'description'
    from /Library/Ruby/Site/1.8/usb.rb:341:in 'inspect'

Finally installing ruby-usb

$ sudo make install
mkdir -p /Library/Ruby/Site/1.8/universal-darwin9.0
/usr/bin/install -c -m 0755 usb.bundle /Library/Ruby/Site/1.8/universal-darwin9.0
/usr/bin/install -c -m 644 ./lib/usb.rb /Library/Ruby/Site/1.8

Example program

require 'usb'
require 'pp'

USB.devices.each do |dev|
     pp dev
#<USB::Device 029/001 05ac:8005 (Full speed Hub)>
#<USB::Device 029/002 05ac:021b Apple Computer Apple Internal Keyboard / Trackpad ? (HID (01,01), HID (01,02), HID (00,00))>
#<USB::Device 061/001 05ac:8005 (Full speed Hub)>
#<USB::Device 093/001 05ac:8005 (Full speed Hub)>
#<USB::Device 093/002 05ac:8240 (HID (00,00))>
#<USB::Device 125/001 05ac:8005 (Full speed Hub)>
#<USB::Device 253/001 05ac:8006 (Hi-speed Hub with single TT)>
#<USB::Device 253/002 05ac:8501 (Vendor specific (ff,ff))>

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