Design Metrics of Embedded Systems
A Design Metric is a measurable feature of the system’s performance, cost, time for implementation and safety etc. Most of these are conflicting requirements i.e. optimizing one shall not optimize the other: e.g. a cheaper processor may have a lousy performance as far as speed and throughput is concerned.
1. NRE cost (nonrecurring engineering cost)
It is one-time cost of designing the system. Once the system is designed, any number of units can be manufactured without incurring any additional design cost; hence the term nonrecurring.
2. Unit cost
The monetary cost of manufacturing each copy of the system, excluding NRE cost.
3. Size
The physical space required by the system, often measured in bytes for software, and gates or transistors for hardware.
4. Performance
The execution time of the system
5. Power Consumption
It is the amount of power consumed by the system, which may determine the lifetime of a battery, or the cooling requirements of the IC, since more power means more heat.
6. Flexibility
The ability to change the functionality of the system without incurring heavy NRE cost. Software is typically considered very flexible.
7. Time-to-prototype
The time needed to build a working version of the system, which may be bigger or more expensive than the final system implementation, but it can be used to verify the system’s usefulness and correctness and to refine the system’s functionality.
8. Time-to-market
The time required to develop a system to the point that it can be released and sold to customers. The main contributors are design time, manufacturing time, and testing time. This metric has become especially demanding in recent years. Introducing an embedded system to the marketplace early can make a big difference in the system’s profitability.
9. Maintainability
It is the ability to modify the system after its initial release, especially by designers who did not originally design the system.
10. Correctness
This is the measure of the confidence that we have implemented the system’s functionality correctly. We can check the functionality throughout the process of designing the system, and we can insert test circuitry to check that manufacturing was correct.
The Performance Design Metric
Performance of a system is a measure of how long the system takes to execute our desired tasks.
The two main measures of performance are:
Latency or response time
This is the time between the start of the task’s execution and the end. For example, processing an image may take 0.25 second.
Throughput
This is the number of tasks that can be processed per unit time. For example, a camera may be able to process 4 images per second
1. NRE cost (nonrecurring engineering cost)
It is one-time cost of designing the system. Once the system is designed, any number of units can be manufactured without incurring any additional design cost; hence the term nonrecurring.
2. Unit cost
The monetary cost of manufacturing each copy of the system, excluding NRE cost.
3. Size
The physical space required by the system, often measured in bytes for software, and gates or transistors for hardware.
4. Performance
The execution time of the system
5. Power Consumption
It is the amount of power consumed by the system, which may determine the lifetime of a battery, or the cooling requirements of the IC, since more power means more heat.
6. Flexibility
The ability to change the functionality of the system without incurring heavy NRE cost. Software is typically considered very flexible.
7. Time-to-prototype
The time needed to build a working version of the system, which may be bigger or more expensive than the final system implementation, but it can be used to verify the system’s usefulness and correctness and to refine the system’s functionality.
8. Time-to-market
The time required to develop a system to the point that it can be released and sold to customers. The main contributors are design time, manufacturing time, and testing time. This metric has become especially demanding in recent years. Introducing an embedded system to the marketplace early can make a big difference in the system’s profitability.
9. Maintainability
It is the ability to modify the system after its initial release, especially by designers who did not originally design the system.
10. Correctness
This is the measure of the confidence that we have implemented the system’s functionality correctly. We can check the functionality throughout the process of designing the system, and we can insert test circuitry to check that manufacturing was correct.
The Performance Design Metric
Performance of a system is a measure of how long the system takes to execute our desired tasks.
The two main measures of performance are:
Latency or response time
This is the time between the start of the task’s execution and the end. For example, processing an image may take 0.25 second.
Throughput
This is the number of tasks that can be processed per unit time. For example, a camera may be able to process 4 images per second
Need for RTOS in Embedded systems
- Meeting deadlines
- Deterministic behaviour
- Physical and memory size
- Prioritized tasks
- Minimum interrupt latency
- Watchdog timer & vectored interrupt
- Small footprint
- Reliable system