USB之Main item, Local item和Global item 的作用范围与归类

https://doc.micrium.com/display/OSUM50300/USB+Device+HID+Class+Overview

report descriptor –> items

(1) main item: defines (IN, OUT, Feature) or groups (Collection, End of Collection) types of data fields;

(2) local/global item: sets data properties;

归类

1, Main

. IN;

.OUT;

.Feature;

.Collection;

.End of Collection;

2, Global

. Usage Page; but Usage is Local;

. Logical Min.; e.g. logic ‘0’;

. Logical Max.; e.g. logic ‘1’;

. Physical Min.;

. Physical Max.;

. Unit Exponent; w/ 10 as base, from –8 to 7;

. Unit; e.g. ms;

. Report Size; number of bits in report field (key info transmitted in main item);

. Report ID;

. Report Count;

. Push; Push a copy of the global item state table(一个状态表) on the CPU stack;

. Pop; Replaces the item state table w/ the last structure from the stack;

3, Local

. Usage; inform the vendor’s suggested use of a specific control(s);

. Usage Min.; the starting usage associated w/ an array or a bitmap;

. Usage Max.; the ending usage associated w/ an array or a bitmap;

. Designator Index; location of the body part of a control; points to a designator in the Physical descriptor;

. Designator Min.; the starting designator associated w/ an array or a bitmap;

. Designator Max.; the ending designator associated 2/ an array or a bitmap;

. String Index; index to a String descriptor; it allowa a string to be associated 2/ a particular item or control;

. String Min.;

. String Max.;

. Delimiter; defines the beginning or end of a set of local items.