Architecture of an Embedded System

ASIC: Application Specific Integrated Circuit: for specific functions like motor control, data modulation etc.

Microcontroller(μC): A family of microprocessors

Real Time Operating System (RTOS): contains all the software for the system control and user interface

Controller Process: The overall control algorithm for the external process. It also provides timing and control for the various units inside the embedded system.
Digital Signal Processor (DSP) a typical family of microprocessors

DSP assembly code: code for DSP stored in program memory

Dual Ported Memory: Data Memory accessible by two processors at the same time

CODEC: Compressor/Decompressor of the data

User Interface Process: The part of the RTOS that runs the software for User Interface activities

Controller Process: The part of the RTOS that runs the software for Timing and Control amongst the various units of the embedded system



The above architecture represents a hypothetical Embedded System (we will see more realistic ones in subsequent examples). More than one microprocessor (2 DSPs and 1 μC) are employed here to carry out different tasks. As we will learn later, the μC is generally meant for simpler and slower jobs such as carrying out a Proportional Integral (PI) control action or interpreting the user commands etc. The DSP is a more heavy duty processor capable of doing real time signal processing and control. Both the DSPs along with their operating systems and codes are independent of each other. They share the same memory without interfering with each other. This kind of memory is known as dual ported memory or two-way post-box memory. The Real Time Operating System (RTOS) controls the timing requirement of all the devices. It executes the over all control algorithm of the process while diverting more complex tasks to the DSPs. It also specifically controls the μC for the necessary user interactivity. The ASICs are specialized units capable of specialized functions such as motor control, voice encoding, modulation/demodulation (MODEM) action etc. They can be digital, analog or mixed signal VLSI circuits. CODECs are generally used for interfacing low power serial Analog-to-Digital Converters (ADCs). The analog signals from the controlled process can be monitored through an ADC interfaced through this CODEC.