UM0851 datasheet(175/245 Pages) STMICROELECTRONICS

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UM0851

Human interface device (HID) drivers

Doc ID 16604 Rev 2

175/245

Figure 46.

Touchscreen software architecture

7.1.3

Touchscreen driver overview

Input device layer

The kernel's input subsystem layer unifies the interface to different drivers that handle

diverse classes of data-input devices such as keyboards, mice, and touchscreens, The

kernel's input subsystem layer provides a uniform way of handling of functionally similar

input devices even when they are physically different. For example, all mice, such as PS/2,

USB or Bluetooth, are treated alike.

It has an easy to use event interface for dispatching input reports to user applications. The

driver does not have to create or manage /dev nodes and related access methods. Instead,

it can simply invoke input APIs to send mouse movements, key presses, or touch events

upstream to user land. Applications such as X Windows work seamlessly over the event

interfaces exported by the input subsystem layer.

Touchscreen driver basics

The touchscreen driver has a state machine which gets called every 100 ms and reads both

ADC channels. The state machine has 3 states, as shown in Figure 47.

User application space

Kernel space

Hardware

Touchscreen driver

ADC + GPIO

CLCD panel

Input device layer

X, QT, GTK

UM0851 Datasheet(PDF) 175 Page - STMicroelectronics