Tänane küsimuste ja vastuste seanss jõuab meile viisakalt SuperUserini - Stack Exchange'i ja kogukonnapõhiste Q & A veebisaitide rühmitusse.
Küsimus
SuperUser lugeja Ne Mo tahab teada, kas USB klaviatuurid ainult signaale või kui nad saavad neid ka:
A USB keyboard does not need to receive any signals from a computer, just power, right? Or does it need to receive signals as well as send them?
Kas USB klaviatuurid saadavad ainult signaale või saavad nad ka neid?
Vastus
SuperUseri kaasautorid LawrenceC ja Dmitri Grigorjev on meie jaoks vastus. Esiteks, LawrenceC:
From the “Device Class Definition for Human Interface Devices (HID)” specification:
Järgneb Dmitri Grigorjevi vastus:
Any USB device regardless of its class requires bidirectional communication to function. Every USB device (or function in terms of USB specifications) is represented as a set of endpoints which can be thought of as buffers which accept or receive data. However, even endpoints which can only send data wait for a special packet called a token before they can reply:
Even so-called interrupt transfers are done in this way, with the USB host polling connected devices using token packets. What differs between regular (bulk) transfers and interrupt transfers is that the polling time is small and guaranteed in the latter case. Still, all transfers are initiated by the host.
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