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Several years ago, I worked with software engineers who did "voice over
Ethernet and long haul networks", which is essentially voice over IP. Some
suggestions based on that experience:
(1) use a mu-law or a-law encoding to get 16 bit audio down to 8-bit audio
to conserve bandwidth and packet size This method is also robust in dealing with
lost packets. If your use CVSD or other low-bit rate encoding schemes for voice,
you incur additional delays, require additional processing power, and have
problems with lost packets causing the decoder to lose synchronization and
reproduction accuracy, as well as having nasty clicks and squawks in the
received audio strearm.
(2) you will need a network interface--Ethernet is a good choice.
(3) Use of UDP as network protocol is effective.
(4) There are numerous articles in Circuit Cellar Ink magazine about
connecting Ethernet interfaces to microcontrollers--check issues in the last
couple of years to give you a guide as to how to attach an Ethenet IC to a
DSP IC.
(5) You will need to buffer the audio on both the transmitting and
receiving ends.
(6) You may wish to put about a 500 millisecond delay (or perhaps a lesser
delay of say,100 milliseconds) to allow time to build up the transmit buffer and
give the receiver buffer time to receive possibly delayed packets to ensure a
continuous voice stream.
(7) an 8 KHz sample rate is usually adequate for voice--this is telephone
toll quality for speech, and supports a 3.3 KHz audio bandwidth. Wider
bandwidths are achieveable with faster sample rates, of course.
(8) a header or sub-header giving connectivity information may be
helpful.
MW Ron <m...@metrowerks.com> wrote:
dsp_devil wrote:
> I just bought a
Motorola 56858 EVM and along with it came the
> Codewarrior software.
I'm trying to implement a VoIP system. However,
> i have not had
any prior experience with either the hardware or
> software. Can anyone
give some advice as to a good place to start on
> such a project. Are
there any open source websites that would be
> helpful for my
purposes.
To learn how to use CodeWarrior, I'd suggest you
do a quick run through of
the the DSP course on CodeWarrior
<http://www.codewarrioru.com> It is self
paced so you can do it
all at once now. While it isn't going to show you
exactly what
you want it will help you see how CodeWarrior works and all of
that.
Ron Programming Motorola's
DSP
Course Description
This course will provide you with the basic concepts of programming
embedded
systems. You will learn what digital signal processors (DSPs) are,
and how
their capabilities make them the core part of the embedded computer
systems
found in everyday devices such as consumer electronics. Along the
way,
you'll learn to program Motorola's DSP56824, DSP56803 and
DSP56805
processors. You'll use Metrowerks' CodeWarrior
development tools to write
DSP programs in C. A built-in simulator program
lets you write and debug DSP
programs on your desktop PC without special
hardware. When you've completed
this course, you'll appreciate
the skilled programming behind the smooth
operation of that cellular phone
or digital camera.
--
Check out the
codewarrior.* usenet newsgroups
for
assistance with your programming
questions.
Ron Liechty - M...@metrowerks.com -
http://www.metrowerks.com
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