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28 Cards in this Set
- Front
- Back
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For every MIPS instruction, what are the first two identical steps? |
1. Fetch the instruction from the instruction memory using the program counter (PC). 2. Read one or two registers, using fields of the instruction to select the registers to read. |
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What is the program counter (PC)? |
The register containing the address of the instruction in the program being executed. |
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What are the three instruction classes? |
1. memory-reference 2. arithmetic-logical 3. branches |
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What is a multiplexor? |
Also known as a data selector, it is a logic element that selects from among several inputs based on the setting of its control lines. |
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What does the control unit do? |
It takes an instruction as an input, and determines how to set the control lines for the functional units and multiplexors. |
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What is a combinational element? |
It is an element that operates on data values. Its output depends only on the current input. E.G. the ALU. |
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What is a state element? |
An element that maintains "state" with internal storage, e.g. data memories or registers. |
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What are the minimum inputs & outputs for a state element? |
The minimum inputs are the data value to be written into the element and the clock, which determines when the data value is written. It output is the value stored on the last clock. |
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When can a state element be written? When can it be read? |
The clock is used to determine when the state element should be written; a state element can be read at any time. |
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What is a sequential element? |
A sequential element is a logic component that contains state. Its output depends on both its inputs and the contents of its internal state. |
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What is a clocking methodology? |
A clocking methodology defines when signals can be read and when they can be written. |
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What is a clock edge? |
A quick transition from low to high or vice versa. |
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What is edge-triggered clocking? |
A clocking scheme in which all state changes occur on a clock edge. |
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What is a control signal? |
A signal used for multiplexor selection or for directing the operation of a functional unit. |
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What is a data signal? |
A signal that contains information that is operated on by a functional unit. |
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When a signal is asserted, what does that mean? What if it is deasserted? |
If a signal is asserted that means it is logically high, or true. If it is deasserted that means it is logically low, or false. |
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What is a datapath element? |
A unit used to operate on or hold data within a processor. e.g. the instruction and data memories, the register file, the ALU, and adders. |
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What is the relation between datapath elements and instructions? |
Datapath elements are the building blocks for instructions. Each instruction requires different datapath elements in order to function. |
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Where are instructions stored? |
In the special instruction memory. |
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What is the program counter (PC)? |
A register that holds the address of the current instruction. |
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What is the register file? |
A register file is a collection of registers in which any register can be read or written by specifying the number of the register in the file. |
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What is required in order for the register file to write data? |
Two inputs: one to specify the register number to be written and one to supply the data to be written into the register. The write control signal must also be asserted for a write to occur at the clock edge. |
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What are the inputs to the ALU and how wide are they? |
There are two 32-bit data signals and one 4-bit control signal. |
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How wide are the inputs carrying the register number to the register file? Why? |
They are are all 5 bits wide. There are 2^5 = 32 registers. |
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Describe the zero detection function of the ALU. |
It is a 1-bit control signal that is output from the ALU. |
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What elements are needed to implement a simple sequential instruction fetch datapath? |
1. Instruction memory to hold instructions 2. Program counter to hold instruction address 3. Adder to increment the program counter |
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ADD, SUB, AND, OR, and SLT belong to which category of instructions? |
R-type or arithmetic-logical instructions. |
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What 3 operations do R-type or arithmetic-logical instructions all perform? |
1. Read two registers 2. Perform an ALU operation on the contents of the registers 3. Write the result to a register. |
