Re: [libusb] less data length in async bulk transfer with 2 cameras

[Tim R. <ti...@pr...>]

Tim Roberts wrote:
>
> Your pixel stream isn't actually continuous during a frame.  You get 
> continuous pixels during a scanline, then there's a pause during 
> horizontal blanking, and a longer pause during vertical blanking. Your 
> frame must be 640x564, so it takes two scanlines to get a packet ready 
> to send.  If you count the H blanking, does the timing work out?  Will 
> you accumulate more than 3072 bytes in 125 microseconds?  If so, then 
> you will require an external FIFO to survive the bursting.

Also remember this -- when you have a maximum isochronous pipe with 3x 
1024-byte packets per microfame, the spec does not guarantee that those 
packet opportunities will be evenly spaced throughout the microframe, 
nor does it guarantee that the packets will be at the same point in each 
microframe.  Also, if your device is not ready when the first of the 
three requests comes in, then you will miss the entire microframe.  The 
hardware won't ask you for the other two.

-- 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.