![Processor technology
Processors vary in their customization for the problem at hand
15
total = 0
for i = 1 to N loop
total += M[i]
end loop
General-
purpose
processor
Single-
purpose
processor
Application-specific
processor
Desired
functionality](https://image.slidesharecdn.com/l3designmetrics-240828071837-d51e5660/85/design-metrics-for-embedded-systems-and-rtos-15-320.jpg)
design metrics for embedded systems and rtos
- 4. Design challenge – optimizing design metrics • Design metric – A measurable feature of a system’s implementation – Optimizing design metrics is a key challenge 4
- 5. Design challenge – optimizing design metrics Common metrics Unit cost: the monetary cost of manufacturing each copy of the system, excluding NRE cost NRE cost (Non-Recurring Engineering cost): The one- time monetary cost of designing the system Size: the physical space required by the system Performance: the execution time or throughput of the system Power: the amount of power consumed by the system Flexibility: the ability to change the functionality of the system without incurring heavy NRE cost 5
- 6. Design challenge – optimizing design metrics Common metrics (continued) Time-to-prototype: the time needed to build a working version of the system Time-to-market: the time required to develop a system to the point that it can be released and sold to customers Maintainability: the ability to modify the system after its initial release Correctness, safety, many more 6
- 7. Design metric competition improving one may worsen others Expertise with both software and hardware is needed to optimize design metrics Not just a hardware or software expert, as is common A designer must be comfortable with various technologies in order to choose the best for a given application and constraints 7 Size Performance Power NRE cost
- 8. Time-to-market: a demanding design metric Time required to develop a product to the point it can be sold to customers Market window Period during which the product would have highest sales Average time-to-market constraint is about 8 months Delays can be costly 8 Revenues ($) Time (months)
- 9. Losses due to delayed market entry Simplified revenue model Product life = 2W, peak at W Time of market entry defines a triangle, representing market penetration Triangle area equals revenue Loss The difference between the on-time and delayed triangle areas 9 On-time Delayed entry entry Peak revenue Peak revenue from delayed entry Market rise Market fall W 2W Time D On-time Delayed Revenues ($)
- 10. Losses due to delayed market entry (cont.) Area = 1/2 * base * height On-time = 1/2 * 2W * W Delayed = 1/2 * (W-D+W)*(W- D) Percentage revenue loss = (D(3W-D)/2W2 )*100% Try some examples 10 On-time Delayed entry entry Peak revenue Peak revenue from delayed entry Market rise Market fall W 2W Time D On-time Delayed Revenues ($) – Lifetime 2W=52 wks, delay D=4 wks – (4*(3*26 –4)/2*26^2) = 22% – Lifetime 2W=52 wks, delay D=10 wks – (10*(3*26 –10)/2*26^2) = 50% – Delays are costly!
- 11. NRE and unit cost metrics • Costs: – Unit cost: the monetary cost of manufacturing each copy of the system, excluding NRE cost – NRE cost (Non-Recurring Engineering cost): The one-time monetary cost of designing the system – total cost = NRE cost + unit cost * # of units – per-product cost = total cost / # of units = (NRE cost / # of units) + unit cost 11 • Example – NRE=$2000, unit=$100 – For 10 units – total cost = $2000 + 10*$100 = $3000 – per-product cost = $2000/10 + $100 = $300 Amortizing NRE cost over the units results in an additional $200 per unit
- 12. The performance design metric Widely-used measure of system, widely-abused Clock frequency, instructions per second – not good measures Digital camera example – a user cares about how fast it processes images, not clock speed or instructions per second Latency (response time) Time between task start and end e.g., Camera’s A and B process images in 0.25 seconds Throughput Tasks per second, e.g. Camera A processes 4 images per second Throughput can be more than latency seems to imply due to concurrency, e.g. Camera B may process 8 images per second (by capturing a new image while previous image is being stored). Speedup of B over S = B’s performance / A’s performance Throughput speedup = 8/4 = 2 12
- 13. Three key embedded system technologies Technology A manner of accomplishing a task, especially using technical processes, methods, or knowledge Three key technologies for embedded systems Processor technology IC technology Design technology 13
- 14. Processor technology The architecture of the computation engine used to implement a system’s desired functionality Processor does not have to be programmable “Processor” not equal to general-purpose processor 14 Application-specific Registers Custom ALU Datapath Controller Program memory Assembly code for: total = 0 for i =1 to … Control logic and State register Data memory IR PC Single-purpose (“hardware”) Datapath Controller Control logic State register Data memory index total + IR PC Register file General ALU Datapath Controller Program memory Assembly code for: total = 0 for i =1 to … Control logic and State register Data memory General-purpose (“software”)
- 15. Processor technology Processors vary in their customization for the problem at hand 15 total = 0 for i = 1 to N loop total += M[i] end loop General- purpose processor Single- purpose processor Application-specific processor Desired functionality
- 16. General-purpose processors Programmable device used in a variety of applications Also known as “microprocessor” Features Program memory General datapath with large register file and general ALU User benefits Low time-to-market and NRE costs High flexibility “Pentium” the most well-known, but there are hundreds of others 16 IR PC Register file General ALU Datapath Controller Program memory Assembly code for: total = 0 for i =1 to … Control logic and State register Data memory
- 17. Single-purpose processors Digital circuit designed to execute exactly one program a.k.a. coprocessor, accelerator or peripheral Features Contains only the components needed to execute a single program No program memory Benefits Fast Low power Small size 17 Datapath Controller Control logic State register Data memory index total +
- 18. Application-specific processors • Programmable processor optimized for a particular class of applications having common characteristics – Compromise between general-purpose and single-purpose processors • Features – Program memory – Optimized datapath – Special functional units • Benefits – Some flexibility, good performance, size and power 18 IR PC Registers Custom ALU Datapath Controller Program memory Assembly code for: total = 0 for i =1 to … Control logic and State register Data memory
- 19. Architectures We must be clear about the architecture that we are going to use for design of ES It has also got a wide variety of choices, to be chosen according to the given application. The choices are as follows Application-specific Architecture :- - Controller Architecture - Datapath Architecture - Finite state machine with datapath General Purpose Architecture :- - CISC - RISC - Vector machine - VLIW ( Very Long Instruction Word Computer )
- 20. Need for RTOS in Embedded systems Meeting deadlines Deterministic behavior Physical and memory size Prioritized tasks Minimum interrupt latency Watchdog timer & vectored interrupt Small footprint Reliable system