Altera CRC Compiler Bedienungsanleitung PDF herunterladen (Seite 22)

3–6 Chapter 3: Functional Description

Parameters

CRC Compiler User Guide © November 2009 Altera Corporation

Preliminary

Parameters

You specify the parameters for the CRC Compiler MegaCore functions using the

MegaWizard interface. Table 3–1 describes each available parameter.

Table 3–1. MegaWizard Control Settings

Parameter Description

CRC Generator Creates a generator MegaCore function

CRC Checker Creates a checker MegaCore function

Number of CRC Channels Specifies the number of CRCs supported. All input and output signals are shared

among the channels. Hence, only 1 channel can be processed at any one time.

Datapath Selects the width of the data input

Symbols per word Specifies the number of symbols in a datapath, and thus defines the width of each

symbol in bits. A symbol represents the smallest unit of data in a word. For

example, if Datapath is set to 32 bits and Symbols per word is set to 4, the width of

each symbol is 8 bits.

Process low-numbered bit in each

symbol first

Processes each symbol in reverse order. For example, given the Datapath is 12 bits

and Symbols per word is 3, turning on this parameter causes the MegaCore

function to process “abcd efgh ijkl” as “dcba hgfe lkji”.

Process low-numbered symbol first Processes the symbols in reverse order. For example, given the Datapath is 12 bits

and Symbols per word is 3, turning on this parameter causes the MegaCore

function to process “abcd efgh ijkl” as “ijkl efgh abcd”.

If both parameters, Process low-numbered bit in each symbol first and Process

low-numbered symbol first are turned on, the MegaCore processes the entire data

in reverse order.

signals with flip-flops

Optimize for: speed Inserts logic to increase the maximum clock speed

Optimize for: area Removes logic to reduce logic utilization and latency

CRC Code Selects the generator polynomial by name

Starting value Presets the CRC register to this value before each packet.

Number of leading bits to ignore in

First word

Specifies the number of bits to ignore at the beginning of a packet.

Negate checksum Sets checksum to the one’s complement of the result of the polynomial division.

Not applicable to the CRC checker.

Bit-swap checksum Applies only to CRC Generator. Selecting this parameter reverses the sequence of

the entire output bits. The low-order bits of the remainder are placed in the high-

order bits of the checksum. Select this parameter if data transmission starts from

low-order bit.

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