.Net Micro Framework is a version of .Net Framework suited for devices with limited resources (ex. at least 200 KB of RAM and Flash memory, from ARM7 CPUs with tens of Mhz also without MMU) that runs without an operating system (even if you can use it) as a bootable runtime and that has a tiny version of the CLR (Common Language Runtime) that is called “TinyCLR”. In this way, you can develop your embedded application without using native languages like C/C++ but with managed code C#/VB.Net. Furthermore, you use a prime class IDE like Visual Studio that provides more features than other less friendly embedded development environment.

The most important feature is that this platform defines an abstraction of the underline hardware so that the developer doesn’t have to worry about CPU registries or memory access but he can focus on his application development using an Object Oriented Programming model. Furthermore, there is the great debugging feature (breakpoints and variable watches) inside the IDE typically with a simple USB cable to connect the device to the development workstation.

Figure 5.1 : .Net Micro Framework architecture

Born with the name SPOT (Smart Personal Objects Technology) with a smart watch product from Microsot, today the .Net Micro Framework platform is open source and it is available on CodePlex (http://netmf.codeplex.com) even if there is a Microsoft team that coordinates the development.

For the OEMs (Original Equipment Manufacturer) there is a porting kit that can be used to adapt the platform itself to the specific hardware. Each manufacturer can develop new features or drivers for its target device (HAL, Hardware Abstraction Layer, of the overall architecture) and compiles the source code of the .Net Micro Framework to release a custom hardware that supports this platform. On CodePlex web site there are already some porting for more common hardware and CPUs like SAM7 from Atmel, iMXS from Freescale and STM32 from ST Microelectronics.

One of the well know boards that supports the .Net Micro Framework is Netduino from SecretLabs (http://netduino.com/) that is a “.Net version” of Arduino board (it is pin to pin compatible with that and you can use more of its shields). There are two versions of it : the former is without Ethernet connection and micro SD card reader and it is named Netduino and the latter that supports these features and it is named Netduino Plus. The first generation of these boards was equipped with an Atmel ARM7 CPU and the new generation boards, Netduino 2 and Netduino Plus 2, are equipped respectively with a more powerful CPUs STM32F2 and STM32F4 with more RAM and Flash storage.

Figure 5.2 : Netduino 2 and Netduino Plus 2 boards

Both the boards offer 22 pins (digital and analog with ADC channels) that can be used as GPIO; some of them can be configured to work as UART ports, SPI bus, I2C bus and PWM.

For our example in the next champter, you have to use a Netduino Plus board (Ethernet connectivity is necessary for MQTT!) but you can choose between first or second generation.