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Application Notes
USB devices transfer data in packets. If data is to be sent from the PC, a packet is built up by the application
program and is sent via the device driver to the USB scheduler. This scheduler puts a request onto the list of tasks
for the USB host controller to perform. This will typically take at least 1 millisecond to execute because it will not
pick up the new request until the next ' USB Frame' (the frame period is 1 millisecond).
There is therefore a sizeable overhead (depending on your required throughput) associated with moving the data
from the application to the USB device. If data is sent 'byte at a time' by an application, this will severely limit the
overall throughput of the system as a whole.
It must be stressed that in order to achieve maximum throughput, application programs should send or receive data
using buffers and not individual characters.
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