
Fast Ethernet Controller (FEC)
Freescale Semiconductor
19-37
Figure 19-28. Ethernet Address Recognition—Microcode Decisions
19.5.10 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, 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 six 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 five least significant bits of the hash result select the bit within
the selected register. If the CRC generator selects a bit 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 (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.
The effectiveness of the hash table declines as the number of addresses increases.
Receive Address
I/G Address
?
Exact Match
?
Hash Search
Group Table
Match
?
Hash Search
Individual Table
False
Match
?
False
False
True
True
True
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
Notes:
FCE - field in RCR register (flow control enable)
I/G - Individual/Group bit in destination address (lsb in first byte received in MAC frame)
MCF5329 Reference Manual, Rev 3
Содержание MCF5329
Страница 106: ...ColdFire Core 3 32 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 126: ...Enhanced Multiply Accumulate Unit EMAC 4 20 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 148: ...Cache 5 22 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 154: ...Static RAM SRAM 6 6 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 184: ...Power Management 8 18 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 204: ...Reset Controller Module 10 8 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 220: ...System Control Module SCM 11 16 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 228: ...Crossbar Switch XBS 12 8 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 268: ...General Purpose I O Module 13 40 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 392: ...SDRAM Controller SDRAMC 18 30 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 436: ...Fast Ethernet Controller FEC 19 44 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 564: ...Liquid Crystal Display Controller LCDC 22 44 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 594: ...FlexCAN 23 30 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 678: ...Pulse Width Modulation PWM Module 26 22 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 684: ...Watchdog Timer Module 27 6 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 692: ...Programmable Interrupt Timers PIT0 PIT3 28 8 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 704: ...DMA Timers DTIM0 DTIM3 29 12 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 720: ...Queued Serial Peripheral Interface QSPI 30 16 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 754: ...UART Modules 31 34 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 770: ...I2 C Interface 32 16 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 790: ...Message Digest Hardware Accelerator MDHA 33 20 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 866: ...Debug Module 36 50 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 902: ...Register Memory Map Quick Reference A 26 Freescale Semiconductor MCF5329 Reference Manual Rev 3...