7
This became apparent to us when we found about the software’s reliance on the
Advanced Linux Sound Architecture (ALSA). The ALSA libraries, drivers and utilities
were supposed to be compiled and installed on the machine running the software. This
was however not possible with the PCM-5896 as it was not equipped for compilation and
development. An example of this limitation was unavailability of the make utility. We
tried to circumvent this by transferring the already compiled object files under
/lib/modules/misc under Linux but we were unsuccessful in getting the ALSA drivers to
load with the modprobe utility. This was because they were not compatible with the
configuration of the kernel on the Single Board Computer. We discovered this after a
couple of frantic calls to our vendor who informed us that their product would actually be
incompatible with ALSA at a very low level due to the configuration of the pre-installed
2.2.14 kernel at compile time. The lack of configuration utilities on our Single Board
Computer ( typical of Linux installation on embedded applications of this type ) left us
even less room to maneuver in. Due to this turn of events, we were forced with two
choices: change the command line Voice over IP code in order to eliminate its reliance on
ALSA and use the Open Sound System (OSS) instead or choose another application that
did not rely on ALSA. We felt that figuring out the workings of the VoIP software would
involve a steep learning curve and would therefore be unsuitable to our limited time
frame. This left us searching frantically for another application that implemented Voice
over IP with some promise of working on an embedded platform. We were unsuccessful
in finding any that was distributed as a binary, something that we were looking for due to
the lack of compilation utilities on our Single Board Computer. We came across two
programs: SIMPH323 and Ohphone, both of which were source downloadable from
http://www.openh323.org/. We were quite skeptical about getting either of these to work
on our embedded system as they relied on the PWLB library package whose source was
also freely available on the same website. This package would have to be compiled on the
desktop and then the library structure would have to be recreated on our Single Board
Computer. This meant that we would have to run the risk of those libraries being
incompatible with our newer 2.2.14 kernel on our embedded system. We decided to go
with the first application we downloaded, SIMPH323, which had very excellent
directions for compilation and installation as did the PWLIB library. After experimenting
with transferring the relevant libraries to another Desktop, we were able to get
SIMPH323 to work over wired Ethernet. This gave us some encouragement to try the
same approach on our Single Board Computer. When testing with the PCM-5896 also
proved successful, we decided to adopt SIMPH323 as our embedded software application
of choice.
4.2.2 DRIVERS
4.2.2.1 SOUND DRIVERS
As mentioned before, the ALSA sound drivers were found to be necessary for our initial
choice of Voice over IP software. However, when it became evident that it would not be
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