Belkin F8E211 Guía de usuario descargar pdf (Pagina 22)

How a class driver works  2006, QNX Software Systems GmbH & Co. KG.

USB enumerator

With the QNX Neutrino OS, the USB enumerator attaches to the USB

stack and waits for device insertions. When a device insertion is

detected, the enumerator looks in the conﬁguration manager’s

database to see which class driver it should start. It then starts the

appropriate driver, which provides for that class of device. For

example, a USB Ethernet class driver would register with

io-net

and bring the interface up.

For small, deeply embedded systems, the enumerator isn’t required.

The class drivers can be started individually — they’ll wait around for

their particular devices to be detected by the stack. At that point,

they’ll provide the appropriate services for that class of device, just as

if they’d been started by the enumerator. When a device is removed,

the enumerator will shut down the class driver.

How a class driver works

A class driver typically performs the following operations:

1 Connect to the USB stack (usbd

connect()) and provide two

callbacks: one for insertion and one for removal.

2 In the insertion callback:

2a Connect to the USB device (usbd

attach()).

2b Get descriptors (usbd

descriptor()).

2c Select the conﬁguration (usbd

select conﬁg()) and

interface (usbd

select interface()).

2d Set up communications pipes to the appropriate endpoint

(usbd

open pipe()).

3 In the removal callback, detach from the USB device

(usbd

detach()).

4 Set up all data communications (e.g. reading and writing data,

sending and receiving control information, etc.) via the

usbd

setup *() functions (usbd setup bulk(),

usbd

setup interrupt(), etc.).

10 Chapter 2 Overview November 2, 2006

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