ch5 - Embedded Systems Design: A Unified Hardware/Software...

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1 Embedded Systems Design: A Unified Hardware/Software Introduction Chapter 5 Memory
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2 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Outline Memory Write Ability and Storage Permanence Common Memory Types Composing Memory Memory Hierarchy and Cache Advanced RAM
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3 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Introduction Embedded system’s functionality aspects Processing processors transformation of data Storage memory retention of data Communication buses transfer of data
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4 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Memory: basic concepts Stores large number of bits m x n : m words of n bits each k = Log 2 ( m ) address input signals or m = 2^k words e.g., 4,096 x 8 memory: 32,768 bits 12 address input signals 8 input/output data signals Memory access r/w: selects read or write enable: read or write only when asserted multiport: multiple accesses to different locations simultaneously m × n memory n bits per word m words enable 2 k × n read and write memory A 0 r/w Q 0 Q n-1 A k-1 memory external view
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5 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Write ability/ storage permanence Traditional ROM/RAM distinctions ROM read only, bits stored without power RAM read and write, lose stored bits without power Traditional distinctions blurred Advanced ROMs can be written to e.g., EEPROM Advanced RAMs can hold bits without power e.g., NVRAM Write ability Manner and speed a memory can be written Storage permanence ability of memory to hold stored bits after they are written Write ability and storage permanence of memories, showing relative degrees along each axis (not to scale). External programmer OR in-system, block-oriented writes, 1,000s of cycles Battery life (10 years) Write ability EPROM Mask-programmed ROM EEPROM FLASH NVRAM SRAM/DRAM Storage permanence Nonvolatile In-system programmable Ideal memory OTP ROM During fabrication only External programmer, 1,000s of cycles External programmer, one time only External programmer OR in-system, 1,000s of cycles In-system, fast writes, unlimited cycles Near zero Tens of years Life of product
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6 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Write ability Ranges of write ability High end processor writes to memory simply and quickly e.g., RAM Middle range processor writes to memory, but slower e.g., FLASH, EEPROM Lower range special equipment, “programmer”, must be used to write to memory e.g., EPROM, OTP ROM Low end bits stored only during fabrication e.g., Mask-programmed ROM In-system programmable memory Can be written to by a processor in the embedded system using the memory Memories in high end and middle range of write ability
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ch5 - Embedded Systems Design: A Unified Hardware/Software...

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