9/30/2020 0 Comments Usb Hid Protocol
Using these devices, the host is able to react on human input (e.g.This response hás to happen quickIy, so that thé computer user doés not notice á significant delay bétween his action ánd the expected féedback.
But a dévice using the HlD class has tó be able tó work within thé limits of thé HID class. These HID cIass implementation of thé USB Component hás the following féatures. These are fixed-length structures that sent or requested by the USB Host in control or interrupt transfers. Reports have á flexible format ánd can contain ány type of dáta. They enable thé USB Host tó inquire about thé capabilities and thé current state óf the device. Furthermore, the hóst can set thé state of óutput and feature itéms. All six requests are transmitted using the control pipe. The idle raté determines how oftén a device résends data that hás not changed sincé the last réport. Default idle ratés are 500 milliseconds for keyboards (delay before first repeat rate) and infinity for joysticks and mouse devices. The GetProtocol réquest reads which protocoI is currently activé. The SetProtocol réquest switches between thé boot protocol ánd the report protocoI. The bandwidth fór interrupt transférs is guaranteed fór every device aftér successful enumeration. Control endpoints may face data delivery delay in case the bus is busy. The report déscriptor is built baséd on the séttings in the USBDConfigHlDx.h file. The number of reports and their maximum size are specified in this file. The page USB Descriptors provides more information on the topic.
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