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Christian Légaré
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Re: Nov 28 - Day 3: Understanding the USB Protocol
Christian Légaré   11/28/2012 3:06:12 PM
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Can you achieve a overall sampling rate of 100Hz for up to 32 USB FS devices connected, when the payload is 4 floats per device. Could this be achieve with HID/Joystick type class, or should I go directly with a custom class??

 

We will have to do the math. First, HID is the right class to use, because it is peioritized by the Host.

(Your 4 floats are 64 bits each? this would mean 32 bytes per transfer)

Second, let's look at the Full Spee table for Interrupt transfer using 32 bytes transfer and see the maximum throughput.

 

At 100Hz, that would mean once every 10 frames. Or stated otherwise, that would mean you can server 3.2 device per frame and have covers the 32 devices in 10 frames.



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