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. |
|
DSP56858-VoIP
Started by ●January 18, 2004
Reply by ●January 19, 20042004-01-19
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 - - http://www.metrowerks.com |
|
Reply by ●January 20, 20042004-01-20
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: |
Reply by ●February 17, 20042004-02-17
I had a further thought about VoIP in general, and was wondering if there
was any comment on the following:
VoIP, as I understand it, runs in some form of Ethrnet style packet
structure at its most basic level.
Assuming these packets are not encoded or encrypted, wouldn't it be
extremely easy for some one to "wire tap" the users on a VoIP based system,
whether voice telephone or data? Assuming it's possible to read the packet
headers, decoding the payload and figuring out who it belongs to should be
easy.
I know there are some actual telephone systems that are VoIP. I
wonder if they deal with this issue.
MW Ron <m...@metrowerks.com> wrote: dsp_devil wrote: |