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Max Isochronous Endpoint Size for TM4C1290NCP

Craig Fahrenkrug
Prodigy 185 points

I want to hook a webcam up to a TM4C1290NCP device.   

The webcam profile shows that at 640x480 it requires 147.456Mbps in isochronous mode.

When I do the math for this mode, I calculate that each packet shall hold about 2K data bytes per transmission.  

The datasheet says:

" 4 KB dedicated endpoint memory: one endpoint may be defined for double-buffered 1023-byte isochronous packet size"

The way I read this, I believe that this device will be insufficient buffer size for this endpoint to work correctly.    

I am new at reading USB specs, so I wanted to have some help.   

Also if this is not the right chip to do this, what low cost chip would you use to access a USB camera that was mentioned above?

Thanks,

Craig

  • 0
    TI__Guru**** 244400 points
    Hello Craig,

    A double buffered would mean 2046 byte of isochronous data with an interrupt generated when one 1023 byte buffer is full. Thus you can still read a full 2K (assuming the math would mean 2000 and not 2048 byte). Secondly the use of the webcam would require HS Mode of transfer since FS would be upto 12Mbps only.

    The next thing to keep in mind is that application in the webcam can split it to smaller packet size allowing for smaller buffers to be used.

    Regards
    Amit