Embedded systems and Microcontroller basics

What we will understand:

1] Embedded system definition

2] Features of Embedded system

3] Microprocessor vs Microcontroller

4] Types of CPU architecture

5] RISC and CISC Architecture for CPU

6] Compiler

7] Debugger, Simulator, and Emulator

8] Address bus, Data bus, and Control Bus

9] 8 bit, 16 bit, 32-bit Controllers

10] What other components does a basic embedded system require?

Before starting this topic, I would like the reader to know that he should have basic knowledge of Electronics and Computers. Like what is basically a microcontroller or a microprocessor and some terms like the OS, how does an ALU or microcontroller or processor process? Just a brief understanding of such topics should be great.

1] Embedded system:

An embedded system is a combination of mechanical, electrical, and electronic hardware and software designed for a specific function. It is a system that is placed in another system. A simple system can be defined as an input, processing, and output. Further, there comes a part of the feedback and then sensing. Now, for embedded systems, it’s not like the computer which does the general-purpose tasks. It is different than Computer systems. For example, a computer is a general system where at the same time we can play music, handle some of the applications (like in a windows PC it might) be an excel sheet and Chrome with some software for downloading and at the same time we would be coding in Anaconda or IntelliJ, etc. So, here, there is no certain task which of high priority or something that is not given prime importance rather the others. For example, if we consider a Mobile, its first priority is to receive calls, and later comes the other stuff like the applications it is playing.

An embedded system is something that senses something through a sensor, processes it through its brain or microcontroller, and acts or outputs something depending on it. For example, we have a simple rear parking sensor in an automobile. Considering reversing the car scenario, once the vehicle’s reverse gear is engaged the sensor is activated and it monitors continuously, they are usually ultrasonic sensors that emit the high frequencies waves, and the time it takes to receive these waves back will determine the distance. This is calculated in the small microcontroller and the distance in meters is pushed on the display. So we have a sensor to get the input to the microcontroller, a microcontroller that processes this sensor data and the output, which is the distance before an impact.

2] Features of Embedded system:

• An Embedded system performs a specialized task and performs that repeatedly.
• The system has to be real-time and reactive to the environment with which it works.
• Tightly connected to the memory, peripherals, sensors, and processing fast. No delay in achieving a specialized task that is recommended.
• There is a concept known as hard real-time and soft real-time. Most of the Embedded systems are hard real-time(also known as mission-critical), which means it has to process certain inputs and provide output within a limited time. For soft real-time, it’s not the same.
• Power consumption is always at a price. Limited power consumption, as majorly such systems are to be considered in standalone systems.
• It should be efficient and reliable.
• It should also be secure and safe.

3] Microprocessor vs Microcontroller:

Most of the Embedded systems use Microcontrollers to achieve the tasks, very few of the Embedded systems use Microprocessors. Let us know about the basic differences.

4] Types of CPU architecture:

Be it a Microcontroller or Microprocessor it has to have a CPU, the brain of these chips. The basic differences in these are the Von Neumann architecture and the Harvard architecture.

The basic differences are as shown in the diagram below

So, the basic difference between a Von Neumann architecture is that it has the same memory for the Data and code. In Harvard architecture the Data and Program or code memories are different. The code which runs the instruction is in different memory area and the data which is used for running this code is stored at different location of the memory as separate entities.

Another type of architecture: SHARC(Super Harvard Architecture)

Some of the advanced architectures are as shown below:

A DSP SHARC architecture:

From the above architecture diagrams, it is clear that there are various advances in CPU architectures. Although not a lot of information to digest, we would not get into the details.

5] RISC and CISC Architecture for CPU:

For a CPU, the Architectures depending on the instruction set and use of the processor is done in a certain way which lets another classification of the architecture known as RISC(Reduced instruction set computing) and CISC(Complex instruction set computing) architectures respectively. RISC has simple instructions which almost take only a single cycle for execution. Now, what does it mean when we say one cycle for execution, this is the frequency at which the CPU takes the input, processes it, and provides the output. So, technically a microcontroller has a crystal or RC oscillator which is responsible for the clocking of the processor or controller. We can think of oscillator and operation cycles as the pumping process of the heart. The brain being the Microcontroller or the processor.

Moving on with the RISC and CISC architectures, CISC takes complex instructions and more than one operation cycle. RISC has fixed format instructions whereas CISC has variable format instructions. RISC relies more on the software for execution it is a software-centric design whereas CISC is Hardware centric design of architecture. CISC uses memory cautiously, RISC uses the memory heavily.

6] Compiler:

In an embedded system, majorly the used programming languages have to be very efficient, safe, and well-controlled. The majority of these use C, C++. Coming to the compiler, a compiler is a computer program that translates computer code written in one programming language into another language. The name “compiler” is primarily used for programs that translate source code from a high-level programming language to a lower-level language to create an executable program.

We come across a terminology called Native and cross compiler:

1. Native Compiler :

Native compilers are compilers that generate code for the same platform on which it runs. It converts high language into computer’s native language. For example Turbo C or GCC compiler

2. Cross compiler :

A Cross compiler is a compiler that generates executable code for a platform other than one on which the compiler is running. For example, a compiler that runs on Linux/x86 box is building a program that will run on a separate Arduino/ARM.

Embedded systems majorly use cross compilers.

Compilation process:

7] Debugger, Simulator and Emulator:

Debugger: A debugger or debugging tool is a computer program used to test and debug other programs (the “target” program). The main use of a debugger is to run the target program under controlled conditions that permit the programmer to track its operations in progress and monitor changes in computer resources (most often memory areas used by the target program or the computer’s operating system) that may indicate malfunctioning code.

Simulator: Code is tested for the MCU / system by simulating it on the host computer used for code development. Simulators try to model the behavior of the complete microcontroller in software.

Emulator:

An emulator is a hardware device or software program that enables one computer system (also known as a host) to imitate the functions of another computer system (known as the guest). It enables the host system to run the software, tools, peripheral devices, and other components which are designed for the guest system. Emulators can be of different types, replicating things such as hardware, software, OS, or CPU.

Today, the use of the terms emulator and debugger seems to be interchangeable.

An in-circuit emulator (ICE) provides a window into the embedded system. The programmer uses the emulator to load programs into the embedded system, run them, step through them slowly, and view and change data used by the system’s software.

An emulator gets its name because it emulates (imitates) the central processing unit (CPU) of the embedded system’s computer. Traditionally it had a plug that inserts into the socket where the CPU integrated circuit chip would normally be placed. Most modern systems use the target system’s CPU directly, with special JTAG-based debug access. Emulating the processor, or direct JTAG access to it lets the ICE do anything that the processor can do but under the control of a software developer.

8] Address bus, Data bus, and Control Bus:

There are normally three types of bus in any processor system:

1] An address bus: this determines the location in memory that the processor will read data from or write data to.

2] A data bus: this contains the contents that have been read from the memory location or are to be written into the memory location.

3] A control bus: this manages the information flow between components indicating whether the operation is a read or a write and ensuring that the operation happens at the right time.

9] 8 bit, 16 bit, 32-bit Controllers:

So the bits represent the Data bus length, registers size, and instruction. Now, as the bus width increases the number of cycles to complete certain tasks decreases. Making the 32-bit controllers the fastest. Considering the cost there are no huge differences as such. The CPU performs 8-bit operations on the 8-bit microcontroller, similarly 16 bit and 32-bit operations for 16 bit and 32-bit microcontroller as such. 32-bit controllers give the best precision. Also, the larger the number of bits more is the range for the address bus. The register size does become big but it also leads to more packing of features in the 32-bit controller.

10] What other components does a basic embedded system require?

1] Power supply (regulated)

2] PCB: PCB or development kit containing a circuit having resistors, pulled up or down, capacitors, Crystal Oscillator, LED’s, Microcontroller, Sensors, ASIC’s, JTAG or debug pin, DB9’s or other pins whichever required according to the board being used, LCD or LED small display if required and many others depending on the application

3] Schematics

4] Oscilloscope

5] Debugger or Emulator

6] Software for debugging or ICE(In-Circuit Emulation)

7] Multimeter (and if required a soldering gun)

8] Connecting wires from the Development board to PC and if any other hardware

Embedded software is fun and challenging to learn, stay for more such posts!!