Update README.md

README.md

@@ -21,11 +21,6 @@ make all
 sudo make install
 ```
 
-After installation, you can build your program like this.
-```
-g++ -o your_program_name your_source_code.cpp -lJetsonGPIO 
-```
-
 
 # Setting User Permissions
 
@@ -49,3 +44,169 @@ rules by running:
 ```
 sudo udevadm control --reload-rules && sudo udevadm trigger
 ```
+
+# Library API
+
+The library provides almost same APIs as the the NVIDIA's Jetson GPIO Python library.
+The following discusses the use of each API:  
+
+#### 1. Include the libary
+
+To include the JetsonGPIO use:
+```
+#include <JetsonGPIO>
+```
+
+All public APIs are declared in namespace "GPIO". If you want to make your code shorter, you can use:  
+```
+using namespace GPIO; // optional
+```
+
+To compile your program use:
+```
+g++ -o your_program_name your_source_code.cpp -lJetsonGPIO 
+```
+
+
+#### 2. Pin numbering
+
+The Jetson GPIO library provides four ways of numbering the I/O pins. The first
+two correspond to the modes provided by the RPi.GPIO library, i.e BOARD and BCM
+which refer to the pin number of the 40 pin GPIO header and the Broadcom SoC
+GPIO numbers respectively. The remaining two modes, CVM and TEGRA_SOC use
+strings instead of numbers which correspond to signal names on the CVM/CVB
+connector and the Tegra SoC respectively.
+
+To specify which mode you are using (mandatory), use the following function
+call:
+```
+GPIO::setmode(GPIO::BOARD);
+# or
+GPIO::setmode(GPIO::BCM);
+# or
+GPIO::setmode(GPIO::CVM);
+# or
+GPIO::setmode(GPIO::TEGRA_SOC);
+```
+
+To check which mode has be set, you can call:
+```
+GPIO::NumberingModes mode = GPIO::getmode();
+```
+This function returns an instance of enum class GPIO::NumberingModes. The mode must be one of GPIO::BOARD(GPIO::NumberingModes::BOARD), GPIO::BCM(GPIO::NumberingModes::BCM), GPIO::CVM(GPIO::NumberingModes::CVM), GPIO::TEGRA_SOC(GPIO::NumberingModes::TEGRA_SOC) or GPIO::NumberingModes::None.
+
+#### 3. Warnings
+
+It is possible that the GPIO you are trying to use is already being used
+external to the current application. In such a condition, the Jetson GPIO
+library will warn you if the GPIO being used is configured to anything but the
+default direction (input). It will also warn you if you try cleaning up before
+setting up the mode and channels. To disable warnings, call:
+```
+GPIO::setwarnings(false);
+```
+
+#### 4. Set up a channel
+
+The GPIO channel must be set up before use as input or output. To configure
+the channel as input, call:
+```
+// (where channel is based on the pin numbering mode discussed above)
+GPIO::setup(channel, GPIO::IN);
+```
+
+To set up a channel as output, call:
+```
+GPIO::setup(channel, GPIO::OUT);
+```
+
+It is also possible to specify an initial value for the output channel:
+```
+GPIO::setup(channel, GPIO::OUT, GPIO::HIGH);
+```
+
+
+#### 5. Input
+
+To read the value of a channel, use:
+
+```
+int value = GPIO::input(channel);
+```
+
+This will return either GPIO::LOW(== 0) or GPIO::HIGH(== 1).
+
+#### 6. Output
+
+To set the value of a pin configured as output, use:
+
+```
+GPIO::output(channel, state);
+```
+
+where state can be GPIO::LOW or GPIO::HIGH.
+
+
+#### 7. Clean up
+
+At the end of the program, it is good to clean up the channels so that all pins
+are set in their default state. To clean up all channels used, call:
+
+```
+GPIO::cleanup();
+```
+
+If you don't want to clean all channels, it is also possible to clean up
+individual channels:
+
+```
+GPIO::cleanup(chan1); // cleanup only chan1
+```
+
+#### 8. Jetson Board Information and library version
+
+To get information about the Jetson module, use/read:
+
+```
+std::string info = GPIO::JETSON_INFO;
+```
+
+To get the model name of your Jetson device, use/read:
+
+```
+std::string model = GPIO::model;
+```
+
+To get information about the library version, use/read:
+
+```
+std::string version = GPIO::VERSION;
+```
+
+This provides a string with the X.Y.Z version format.
+
+#### 9. Check function of GPIO channels  
+
+This feature allows you to check the function of the provided GPIO channel:
+
+```
+GPIO::Directions direction = GPIO::gpio_function(channel);
+```
+
+The function returns either GPIO::IN(GPIO::Directions::IN) or GPIO::OUT(GPIO::Directions::OUT) which are the instances of enum class GPIO::Directions.
+
+#### 10. PWM  
+
+See `samples/simple_pwm.py` for details on how to use PWM channels.
+
+The JetsonGPIO library supports PWM only on pins with attached hardware PWM
+controllers. Unlike the RPi.GPIO library, the JetsonGPIO library does not
+implement Software emulated PWM. Jetson Nano supports 2 PWM channels, and
+Jetson AGX Xavier supports 3 PWM channels. Jetson TX1 and TX2 do not support
+any PWM channels.
+
+The system pinmux must be configured to connect the hardware PWM controlller(s)
+to the relevant pins. If the pinmux is not configured, PWM signals will not
+reach the pins! The JetsonGPIO library does not dynamically modify the pinmux
+configuration to achieve this. Read the L4T documentation for details on how to
+configure the pinmux.