Da li USB tipkovnice samo šalju signale ili ih primaju previše?

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Da li USB tipkovnice samo šalju signale ili ih primaju previše?
Da li USB tipkovnice samo šalju signale ili ih primaju previše?

Video: Da li USB tipkovnice samo šalju signale ili ih primaju previše?

Video: Da li USB tipkovnice samo šalju signale ili ih primaju previše?
Video: CS50 2015 - Week 1 - YouTube 2024, Travanj
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Većina nas nikada ne daju mnogo misli na naše klavijature sve dok dobro rade, ali ako za trenutak prestanete razmišljati, šalju samo signale na naše računalo ili postoji aktivan proces naprijed-nazad na poslu ? Danas SuperUser Q & A post ima odgovor na pitanje čudnog čitatelja.
Većina nas nikada ne daju mnogo misli na naše klavijature sve dok dobro rade, ali ako za trenutak prestanete razmišljati, šalju samo signale na naše računalo ili postoji aktivan proces naprijed-nazad na poslu ? Danas SuperUser Q & A post ima odgovor na pitanje čudnog čitatelja.

Današnja pitanja i odgovori nam se javljaju zahvaljujući SuperUseru - podjele Stack Exchange-a, zajednice-driven grupiranja Q & A web stranica.

Pitanje

Čitač SuperUser Ne Mo želi znati donose li USB tipkovnice samo signale ili ih primaju:

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?

Da li USB tipkovnice samo šalju signale ili ih primaju?

Odgovor

Dobavljači SuperUser-a LawrenceC i Dmitry Grigoryev imaju odgovor za nas. Prvo, LawrenceC:

From the “Device Class Definition for Human Interface Devices (HID)” specification:

To change the keyboard LEDs, the keyboard accepts a command to do so. So it is not an “input-only” device (meaning it only outputs data to the host). That being said, there is a negotiation and enumeration process with all USB devices that require a back-and-forth conversation between the host and the device. You cannot have a “read-only” USB device. Even before USB, the computer’s keyboard controller would accept commands because it did a few things besides read the keyboard (reference):
To change the keyboard LEDs, the keyboard accepts a command to do so. So it is not an “input-only” device (meaning it only outputs data to the host). That being said, there is a negotiation and enumeration process with all USB devices that require a back-and-forth conversation between the host and the device. You cannot have a “read-only” USB device. Even before USB, the computer’s keyboard controller would accept commands because it did a few things besides read the keyboard (reference):
Image
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Slijedi odgovor Dmitrij Grigoryev:

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:

The gray boxes represent the USB host while the white boxes represent USB functions (chart source).
The gray boxes represent the USB host while the white boxes represent USB functions (chart source).

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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