On Mon, 2002-04-29 at 12:23, bong siu wrote: > Thank you, Dmitri! > > > The other question is I am currently developing a > > USB > > > Cam. In order to increase the through-put, we are > > > trying to add a Mpeg encoder to the USB cam, so > > the > > > USB bus will only need to transfer Mpeg data. Do > > you > > > guys think that is a good idea? > > > > You would need a very fast CPU in the camera, or a > > dedicated encoder. > > Not only that; someone on the host side must > > decompress the MPEG stream > > to do something with the image - this will require > > some CPU as well. > > Maybe you would be better off using USB 2.0? > > I think I will get the Cypress FX2 for the USB > Interface and use a Xilinx chip for encoding the the > data coming from the Webcam or digital cam. On the > host side, I will write a simple web server which will > connect directly to the USB webcam's driver. The > clients will use a brower or a media player to view > the mpeg streamming out from the webserver. One thing > I am worrying about is the speed. I don't know if this > design will work or not. Any suggestions?
You just outlined a business plan for a small startup company with, let's say, USD $1,000,000 in financing :-) You have -many more- things to worry about, not just performance. a) Choose your sensor. Then choose again because the first one does not work well (after you spent 3 months trying to make it work). b) Choose your USB interface. I am not very familiar with FX2, but somehow I am unsure that an "Enhanced 8051 core" will suffice. c) Choose your sensor controls and image processing CPU. You propose to use an FPGA to do MPEG encoding - very well, I hope you have the VHDL for that ready :-) d) The host side. You propose to bypass v4l interface and dump the raw MPEG stream from your camera into whatever application the client uses to view it. I hope you are very familiar with MPEG synchronization and are absolutely sure that the client can quickly synchronize regardless of when he connected. Also, every 2 or 3 months you need to repeat steps (a) - (c) because the parts that you chose become obsolete and are no longer manufactured. Then you will need to manufacture the SMD PCB because you can't just airwire these components; this will take its usual toll as well. If you are not familiar with Eagle CAD ... you'd better start training :-) Please let me reiterate: this is not an easy project. In my estimate, if you were a startup company, you would need 3 grade A+ engineers and 6 months to get the first (barely working) prototype. Then you'd need twice as long to redo it all and maybe come closer to the manufacturing... If I were to design a camera, I would not use an FPGA for MPEG (if that is what you intend to do). I would take a fast TI DSP, or an ARM7/ARM9 chip instead. I would also consider an off-the-shelf MPEG encoder chip. But probably you already know how to get where you want to be... Thanks, Dmitri
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