updated README.md

README.md

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-# IRext Encoding and Decoding core library
+IRext Encoding and Decoding Core Library
+
+	This project contains IRext core encode algorithm and decode algorithm.
+
+Summary
+
+	IR code is base on 38000Hz or 56000Hz carrier waves, it is identified by the time interval of carrier waves.
+
+	Identical control signal is defined by pairs of physical high and low levels, eg. the NEC encoding bits as below :
+
+(image of IR code)
+
+	The lead code is identified by the 9000us time interval with carrier waves and 4500us interval without carrier waves. The logic 0 is identified by 500us time interval with carrier waves and 500us interval without carrier waves. The logic 1 is identified by 500us time interval with carrier waves and 1500us interval without carrier waves, so are the other types of encoding.
+
+Following are some specifications:
+
+- Physical high level is constituted by carrier waves and physical low level without any carrier waves.
+- Basic protocol is constructed by different types of elements including lead code, end code, splitter, logic 0 and logic 1, different protocol has its own element structure, eg. NEC, upd6121g, tc9012, etc.
+- 1 or more cycles resists in single element, but often 1 cycle.
+- Lead code, end code and splitter takes 1 bit in element, for example, in NEC above, a '9000-4500' indicates 1 logic bit.
+- Logic 0 and logic 1 take 8 bit in an element.
+- Logic 0 and logic 1 could be big endian or little endian.
+- For some of the protocols, logic 0 and logic 1 have bit masks.
+- For some of the protocols, like mi-1 pattern could be in format of binary, quaternary or hexadecimal.
+- For some of the protocols, like RC5 toggles its bits.
+- For some of the protocols, there are 0us time intervals in lead code or end code.
+
+2 kinds of remote control IR code:
+
+- Command code: The receiver receives IR code as commands from emitter, and then adjusts status of itself, eg. control code of TV, DVD.
+- Status code: The receiver receives IR code as status, and applies itself to this status, eg. control code of air conditioner.
+
+Encoder
+
+	The encoder composes compressed remote control IR binaries from plain text in XML format. Different kind of remote control code are differently composed.
+
+Command code
+
+	Command code is composed by 2 parts : protocol segment and control segment which are stored in 2 parts. When encode, the remote control key code would be calculated and translated according to protocol definition and merge separate segments into a complete control frame.
+
+Status code
+
+	Status code is defined by various kinds of tags, indication each essential part in one status control frame. It is especially used for air conditioners.
+
+Decoder
+
+	The decoder decodes IR remote control binaries into IR control frame which is composed by time series illustrated above.
+
+	The input of decode algorithm is the IR remote control binary file or its content in bytes, the keycode and category id get from indexing API. 
+
+	The output of the algorithm is the time series, which can be sent to IR emit driver function to send IR control waves to the family equipment.
+
+	Please refer to https://irext.net/doc/ for details.
+
+