Edge Computing - Embedded Systems

Introduction

Embedded system consists of computer hardware and software, and physical parts, designed to perform a specific task.

Architectures

Reference:

• Hardware and architectures

Build Process

Compilation Toolchain

Hardware Abstraction Layers (HAL)

Embedded system development is about programming at the hardware level but accessing hardware via the hardware abstraction layers (HALs), an interface between hardware and software so that applications can be device independent. The HAL encapsulates the peripherals of a microcontroller, and several API implementations are provided at different levels of abstraction.

Embedded Development

To learn embedded development, it’s best to have access to development board. Embedded development requires some understanding of tasks typically handle by operating system.

The following instructions were extracted from “Software Engineering for Embedded Systems, 2nd Edition, by Mark Kraeling, Robert Oshana”.

• Choose the hardware platform, and understand the hardware details from the following documents:
  • Platform User Guide - contains how to initialize the platform and access peripherals; platform block diagram, reset details, board schematics, and connector pinouts; For example: NXP KW41Z
  • Processor datasheet - aka reference guide, will refer to CPU architecture data sheet containing hardware-specific details, such as voltages and frequencies, bus timing, and any low-level details applicable to the system reset, system initialization, clocking, etc. For example: NXP KW41Z

• Figure out how to initialize the system and program the peripherals, which requires knowledge of both hardware and software. Embedded hardware providers typically include: preconfigured initialization code with the SDK, and sample runtime codes. For example, NXP MCUXpressoIDE The SDK also provides the required cross-development tools (C compiler, linker, debugger, etc.), set of header files, libraries, and sample projects. These files provide utility functions to configure and use the peripherals contained in the device.

• Install the SDK and development IDE

• Download the debugger; such as JTAG debug connection. Connect the reference board to your workstation using the USB cable. You may be prompted to install device drivers to support the JTAG connection. With the board connected, right-click on the project in the project explorer and select “Debug As >”.
  The debugger will reset the target processor, download the binary image to the target, insert a temporary breakpoint at main(), and release the processor from reset. The processor will execute the startup code (memory and variable initialization, etc.) and then halt execution at the temporary breakpoint at main(). At this point the debugger IDE can be used to single step, set breakpoints, examine variables, etc. To execute the program at full speed, press the “F8” function key. The main program will run. To terminate the debug session, press the “CTRL-F2” key.

• Understanding system reset;
  All embedded processors have a well-defined mechanism to handle the power-on reset event. However, the details of these mechanisms will vary based on many factors: CPU architecture, SoC manufacturer, and a long list of optional settings. These settings specify the boot device, bus settings, single-chip mode, clock sources, etc. There are also many ways these settings can be implemented. One way is to use pull-up resistors on specific I/O or bus pins. These pins are read shortly after reset and determine the optional settings for that SoC. After the settings are determined, these pins assume their primary functions. Another method employed on some SoCs is to read the settings from a specific location in flash memory.

  Once the processor has come out of reset with the correct configuration, the boot software is then required to initialize many different subsystems. These initialization steps will be very specific to the SoC being used, the way the device is configured, and which peripherals will be needed by the operating system and/or application software. There are several sources that provide working examples of boot software. These examples can often be found in the semiconductor supplier’s SDKs, commercial RTOS vendor’s SDKs, and open source projects like Linux (www.yoctoproject.org) and FreeRTOS (www.freertos.org). Reading sample boot code operations and identifying the appropriate sections in the previously mentioned documentation is an excellent way to learn how a reference platform like the FDRM-KW41Z is configured and initialized at boot time.

• Understand clock configuration
  The clocking subsystems on modern embedded SoCs are very complex. The Reference Manual contains the detailed information needed to properly configure the clocks.

• Learn I/O Pin Configuration and Initialization

• Learn Interrupt Handlers One of the peripherals most commonly used in embedded designs is the timer. Many of the larger, highly integrated SoCs will contain multiple types of timers, and often support different operating modes and capabilities. Some are designed as periodic interrupt timers (PIT) and can be used to generate interrupts at a constant rate, and others generate periodic waveforms (PWM) or time the rise and fall of input signals (input capture). Other types of timer models can function as counters, using internal or external signals as the event to be counted.

References

• Software Engineering for Embedded Systems, 2nd Edition, by Mark Kraeling; Robert Oshana; see OReilly Safari online;