Скачать презентацию Embedded System Hardware Embedded system hardware is frequently Скачать презентацию Embedded System Hardware Embedded system hardware is frequently

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Embedded System Hardware Embedded system hardware is frequently used in a loop („hardware in Embedded System Hardware Embedded system hardware is frequently used in a loop („hardware in a loop“): actuators Embedded systems: processing - 1 -

Summary: Information processing 1. ASICs 2. Processors • Energy efficient • Code-size efficient • Summary: Information processing 1. ASICs 2. Processors • Energy efficient • Code-size efficient • Run-time efficient • Special features of DSP processors • Multimedia instructions • Very long instruction word machines 3. Reconfigurable hardware 4. Memory Embedded systems: processing - 2 -

Reconfigurable Logic Full custom chips may be too expensive, software may be too slow. Reconfigurable Logic Full custom chips may be too expensive, software may be too slow. Use of configurable hardware; most common form: field programmable gate arrays (FPGAs) Considered e. g. for configuring mobile phone according to local standards; Fast “object recognition”. Example: Xilinx Virtex II FPGAs, Altera Stratix Embedded systems: processing - 3 -

Floor-plan of VIRTEX II FPGAs Embedded systems: processing - 4 - Floor-plan of VIRTEX II FPGAs Embedded systems: processing - 4 -

Virtex II Configurable Logic Block (CLB) Embedded systems: processing - 5 - Virtex II Configurable Logic Block (CLB) Embedded systems: processing - 5 -

Virtex II Pro Devices include up to 4 Power. PC processor cores [© and Virtex II Pro Devices include up to 4 Power. PC processor cores [© and source: Xilinx Inc. : Virtex-II Pro™ Platform FPGAs: Functional Description, Sept. 2002, //www. xilinx. com] Embedded systems: processing - 6 -

Memory For the memory, efficiency is again a concern: • fast (latency and throughput); Memory For the memory, efficiency is again a concern: • fast (latency and throughput); predictable timing • energy efficiency • size • cost • other attributes (volatile vs. persistent, etc) Embedded systems: processing - 7 -

Access-times will be a problem Speed gap between processor and main DRAM increases Speed Access-times will be a problem Speed gap between processor and main DRAM increases Speed • early 60 ties (Atlas): page fault ~ 2500 instructions • 2002 (2 GHz µP): access to DRAM ~ 500 instructions penalty for cache miss soon same as for page fault in Atlas (1. 5 -2 p. a. ) 8 U 4 CP 2 x every 2 years 2 . ). 07 p. a (1 DRAM 1 0 1 2 3 4 5 Embedded systems: processing years [P. Machanik: Approaches to Addressing the Memory Wall, TR Nov. 2002, U. Brisbane] - 8 -

Access times and energy consumption increases with the size of the memory Example (CACTI Access times and energy consumption increases with the size of the memory Example (CACTI Model): "Currently, the size of some applications is doubling every 10 months" [STMicroelectronics, Medea+ Workshop, Stuttgart, Nov. 2003] Embedded systems: processing - 9 -

How much of the energy consumption of a system is memory-related? Mobile PC Thermal How much of the energy consumption of a system is memory-related? Mobile PC Thermal Design (TDP) System Power Other 13% 600/500 MHz u. P 37% Power Supply 10% 600/500 MHz u. P 13% Power Supply 10% Memory+Graphics 12% HDD 9% Mobile PC Average System Power LCD 10" 30% Memory+Graphics 15% LCD 10" 19% Note: Based on Actual Measurements CPU Dominates Thermal Design Power [Courtesy: N. Dutt; Source: V. Tiwari] Embedded systems: processing HDD 19% Multiple Platform Components Comprise Average Power - 10 -

CPU Power Dissipation 42%/40% again memory-related ! IEEE Journal of SSC Nov. 96 Based CPU Power Dissipation 42%/40% again memory-related ! IEEE Journal of SSC Nov. 96 Based on slide by and ©: Osman S. Unsal, Israel Koren, C. Mani Krishna, Csaba Andras Moritz, University of Massachusetts, Amherst, 2001 Embedded systems: processing Proceedings of ISSCC 94 - 11 -

Predictability is a problem • Embedded systems are often real-time systems: – Have to Predictability is a problem • Embedded systems are often real-time systems: – Have to guarantee meeting timing constraints. • Predictability: For satisfying timing constraints in hard realtime systems, predictability is the most important concern; pre run-time scheduling is often the only practical means of providing predictability in a complex system [Xu, Parnas] Time-triggered, statically scheduled operating systems • What about memory accesses? – Currently available caches don‘t solve the problem: • Improve the average case behavior • Use “non-deterministic” cache replacement algorithms Scratch-pad/tightly coupled memory based predictability Embedded systems: processing - 12 -

Hierarchical memories using scratch pad memorys (SPM) Hierarchy Example main SPM Address space processor Hierarchical memories using scratch pad memorys (SPM) Hierarchy Example main SPM Address space processor 0 no tag memory ARM 7 TDMI cores, well-known for low power consumption scratch pad memory FFF. . Embedded systems: processing - 13 -

Scratchpad vs. main memory currents Example: Atmel ARM-Evaluation board current reduction: / 3. 02 Scratchpad vs. main memory currents Example: Atmel ARM-Evaluation board current reduction: / 3. 02 Main Memory (on board) SPM (On-chip) Processor Embedded systems: processing - 14 -

Why not just use a cache ? 1. Predictability? Worst case execution time (WCET) Why not just use a cache ? 1. Predictability? Worst case execution time (WCET) may be large [P. Marwedel et al. , ASPDAC, 2004] Embedded systems: processing - 15 -

Why not just use a cache ? (2) 2. Energy for parallel access of Why not just use a cache ? (2) 2. Energy for parallel access of sets, in comparators, muxes. [R. Banakar, S. Steinke, B. -S. Lee, 2001] Embedded systems: processing - 16 -

Embedded System Hardware Embedded system hardware is frequently used in a loop („hardware in Embedded System Hardware Embedded system hardware is frequently used in a loop („hardware in a loop“): actuators Embedded systems: processing - 17 -

Digital-to-Analog (D/A) Converters Various types, can be quite simple, e. g. : Embedded systems: Digital-to-Analog (D/A) Converters Various types, can be quite simple, e. g. : Embedded systems: processing - 18 -

Output voltage no. represented by x Due to Kirchhoff‘s laws: Current into Op-Amp=0: Hence: Output voltage no. represented by x Due to Kirchhoff‘s laws: Current into Op-Amp=0: Hence: Finally: Embedded systems: processing - 19 -

Possible to reconstruct analog value from digitized value? According to Nyquist theorem: • Analog Possible to reconstruct analog value from digitized value? According to Nyquist theorem: • Analog input to sample-and-hold can be precisely reconstructed from its output, provided that sampling proceeds at double of the highest frequency found in the input voltage and provided voltages remain analog. • Digitizing values in the A/D generates additional uncertainty preventing precise reconstruction of initial values. Can be modeled as additional noise. S/H A/D-converter D/A-converter Interpolate =? Embedded systems: processing - 20 -

Embedded System Hardware Embedded system hardware is frequently used in a loop („hardware in Embedded System Hardware Embedded system hardware is frequently used in a loop („hardware in a loop“): actuators Embedded systems: processing - 21 -

Actuators and output Huge variety of actuators and output devices, impossible to present all Actuators and output Huge variety of actuators and output devices, impossible to present all of them. Microsystems motors as examples (© MCNC): (© MCNC) Embedded systems: processing - 22 -

Actuators and output (2) Courtesy and ©: E. Obermeier, MAT, TU Berlin Embedded systems: Actuators and output (2) Courtesy and ©: E. Obermeier, MAT, TU Berlin Embedded systems: processing - 23 -