ch3_102802 - Embedded Systems Design: A Unified...

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1 Embedded Systems Design: A Unified Hardware/Software Introduction Chapter 3 General-Purpose Processors: Software
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2 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Introduction General-Purpose Processor Processor designed for a variety of computation tasks Low unit cost, in part because manufacturer spreads NRE over large numbers of units Motorola sold half a billion 68HC05 microcontrollers in 1996 alone Carefully designed since higher NRE is acceptable Can yield good performance, size and power Low NRE cost, short time-to-market/prototype, high flexibility User just writes software; no processor design a.k.a. “microprocessor” – “micro” used when they were implemented on one or a few chips rather than entire rooms
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3 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Basic Architecture Control unit and datapath Note similarity to single-purpose processor Key differences Datapath is general Control unit doesn’t store the algorithm – the algorithm is “programmed” into the memory Processor Control unit Datapath ALU Registers IR PC Controller Memory I/O Control /Status
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4 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Datapath Operations Load Read memory location into register ALU operation Input certain registers through ALU, store back in register Store Write register to memory location Processor Control unit Datapath ALU Registers IR PC Controller Memory I/O Control /Status 10 ... ... 10 +1 11 11
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5 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Control Unit Control unit: configures the datapath operations Sequence of desired operations (“instructions”) stored in memory – “program” Instruction cycle – broken into several sub-operations, each one clock cycle, e.g.: Fetch: Get next instruction into IR Decode: Determine what the instruction means Fetch operands: Move data from memory to datapath register Execute: Move data through the ALU Store results: Write data from register to memory Processor Control unit Datapath ALU Registers IR PC Controller Memory I/O Control /Status 10 ... ... load R0, M[500] 500 501 100 inc R1, R0 101 store M[501], R1 102 R0 R1
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6 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Control Unit Sub-Operations Fetch Get next instruction into IR PC: program counter, always points to next instruction IR: holds the fetched instruction Processor Control unit Datapath ALU Registers IR PC Controller Memory I/O Control /Status 10 ... ... load R0, M[500] 500 501 100 inc R1, R0 101 store M[501], R1 102 R0 R1 100 load R0, M[500]
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7 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Control Unit Sub-Operations Decode Determine what the instruction means Processor Control unit Datapath ALU Registers IR PC Controller Memory I/O Control /Status 10 ...
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ch3_102802 - Embedded Systems Design: A Unified...

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