嵌入式开发课件ch4-2.ppt

? 2008 Wayne Wolf Overheads for Computers as Components 2nd ed. Memory aspect ratios 64 M 16 M 8 M 1 4 8 ? 2008 Wayne Wolf Overheads for Computers as Components 2nd ed. Memory access times Memory component access times comes from chip data sheet. Page modes allow faster access for successive transfers on same page. If data doesn’t fit naturally into physical words: A = [(E/w)mod W]+1 Bus performance bottlenecks Transfer 320 x 240 video frame @ 30 frames/sec = 612,000 bytes/sec. Is performance bottleneck bus or memory? ? 2008 Wayne Wolf Overheads for Computers as Components 2nd ed. memory CPU ? 2008 Wayne Wolf Overheads for Computers as Components 2nd ed. Bus performance bottlenecks, cont’d. Bus: assume 1 MHz bus, D=1, O=3: Tbasic = (1+3)612,000/2 = 1,224,000 cycles = 1.224 sec. Memory: try burst mode B=4, width w=0.5. Tmem = (4*1+4)612,000/(4*0.5) = 2,448,000 cycles = 0.2448 sec. Performance spreadsheet ? 2000 Morgan Kaufman Overheads for Computers as Components Parallelism Speed things up by running several units at once. DMA provides parallelism if CPU doesn’t need the bus: DMA + bus. CPU. ? 2008 Wayne Wolf Overheads for Computers as Components 2nd ed. Overheads for Computers as Components ? 2008 Wayne Wolf Overheads for Computers as Components 2nd ed. Bus-Based Computer Systems Designing with microprocessors. Development and debugging. System-level performance analysis. ? 2008 Wayne Wolf Overheads for Computers as Components 2nd ed. System architectures Architectures and components: software; hardware. Some software is very hardware-dependent. ? 2008 Wayne Wolf Overheads for Computers as Components 2nd ed. Hardware platform architecture Contains several elements: CPU; bus; memory; I/O devices: networking, sensors, actuators, etc. How big/fast much each one be? ? 2008 Wayne Wolf Overheads for Computers as Components 2nd ed. Software architecture Functional description must be broken into pieces: division among people; conceptual organization; performance; testabi