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MOTOROLA
Chapter 17. Fast Ethernet Controller (FEC)
17-13
Functional Description
Figure 17-3. Ethernet Address Recognitionq—Microcode Decisions
17.4.9 Hash Algorithm
The hash table algorithm used in the group and individual hash filtering operates as follows.
The 48-bit destination address is mapped into one of 64 bits, which are represented by 64
bits stored in GAUR, GALR (group address hash match) or IAUR, IALR (individual
address hash match). This mapping is performed by passing the 48-bit address through the
on-chip 32-bit CRC generator and selecting the 6 most significant bits of the CRC-encoded
result to generate a number between 0 and 63. The MSB of the CRC result selects GAUR
(MSB = 1) or GALR (MSB = 0). The least significant 5 bits of the hash result select the bit
within the selected register. If the CRC generator selects a bit that is set in the hash table,
the frame is accepted; otherwise, it is rejected.
For example, if eight group addresses are stored in the hash table and random group
addresses are received, the hash table prevents roughly 56/64 (or 87.5%) of the group
address frames from reaching memory. Those that do reach memory must be further filtered
by the processor to determine if they truly contain one of the eight desired addresses.
Receive Address
I/G Address
?
Exact Match
?
Hash Search
Group Table
Match
?
Hash Search
Individual Table
False
Match
?
False
False
True
True
True
NOTES:
FCE - field in RCR register (Flow Control Enable)
I/G - Individual/Group bit in Destination Address (least significant bit in first byte received in MAC frame)
Individual
Group
True
False
True
False
?
Pause Address
FCE
?
Recognition
Reject Frame
Flush from FIFO
Reject Frame
Flush from FIFO
Receive Frame
Receive Frame
Receive Frame
Receive Frame
Содержание ColdFire MCF5281
Страница 1: ...MCF5282UM D Rev 2 1 2004 MCF5282 ColdFire Microcontroller User s Manual Devices Supported MCF5281 ...
Страница 124: ...3 20 MCF5282 User s Manual MOTOROLA EMAC Instruction Set Summary ...
Страница 141: ...MOTOROLA Chapter 5 Static RAM SRAM 5 5 SRAM Programming Model ...
Страница 142: ...5 6 MCF5282 User s Manual MOTOROLA SRAM Programming Model ...
Страница 168: ...6 26 MCF5282 User s Manual MOTOROLA Interrupts ...
Страница 186: ...7 18 MCF5282 User s Manual MOTOROLA Functional Description ...
Страница 228: ...9 22 MCF5282 User s Manual MOTOROLA Functional Description ...
Страница 246: ...10 18 MCF5282 User s Manual MOTOROLA Low Power Wakeup Operation ...
Страница 254: ...11 8 MCF5282 User s Manual MOTOROLA Memory Map and Registers ...
Страница 264: ...12 10 MCF5282 User s Manual MOTOROLA Chip Select Registers ...
Страница 280: ...13 16 MCF5282 User s Manual MOTOROLA Misaligned Operands ...
Страница 314: ...14 34 MCF5282 User s Manual MOTOROLA MCF5282 External Signals ...
Страница 339: ...MOTOROLA Chapter 15 Synchronous DRAM Controller Module 15 25 SDRAM Example ...
Страница 340: ...15 26 MCF5282 User s Manual MOTOROLA SDRAM Example ...
Страница 356: ...16 16 MCF5282 User s Manual MOTOROLA DMA Controller Module Functional Description ...
Страница 408: ...17 52 MCF5282 User s Manual MOTOROLA Buffer Descriptors ...
Страница 446: ...20 24 MCF5282 User s Manual MOTOROLA Interrupts ...
Страница 474: ...22 18 MCF5282 User s Manual MOTOROLA Programming Model ...
Страница 510: ...23 36 MCF5282 User s Manual MOTOROLA Operation ...
Страница 526: ...24 16 MCF5282 User s Manual MOTOROLA I2C Programming Examples ...
Страница 672: ...28 12 MCF5282 User s Manual MOTOROLA Functional Description ...
Страница 718: ...29 46 MCF5282 User s Manual MOTOROLA Motorola Recommended BDM Pinout ...
Страница 750: ...32 8 MCF5282 User s Manual MOTOROLA Ordering Information ...
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