Altera CRC Compiler - Manual (Page 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.
Register all Avalon-ST inputs Buffers data , datavalid , startofpacket , endofpacket , and empty
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.
Register all outputs Buffers crcvalid and checksum , or crcbad with flip-flops.