MPC8540 datasheet(1257/1302 Pages) FREESCALE

1257 / 1302 page

Changes From Revision 0 to Revision 1

MPC8540 PowerQUICC III Integrated Host Processor Reference Manual, Rev. 1

Freescale Semiconductor

A-45

21.6.2.5.3, 21-54

Add the following section after Section 21.6.2.5.2:

21.6.2.5.3 CRC Computation Examples

There are many algorithms for calculating the CRC value of a number.

Refer to the RFC 3309 standard, which can be found at

http://www.faqs.org/rfcs/rfc3309.html, to compute the CRC value for the

purposes of TSEC. The RFC 3309 algorithm uses the following polynomial

to calculate the CRC value:

x32+x26+x23+x22+x16+x12+x11+x10+x8+x7+x5+x4+x2+x1+x0 or

0x04c11db7.

Given a destination MAC address of DA=01000CCCCCCC, the algorithm

results in a CRC remainder value of 0xA29F4BBC.

Bit-reversing the low-order byte of the CRC value (0xBC) yields BR_CRC

= 0x3D = 0b00111101

The high-order 3-bits of the new BR_CRC value are used to select which

32-bit register (of the 8) to use. This example maps the DA to register 1.

High-order 3 bits of BR_CRC: HO_CRC = 0b001 = 1

The low-order 5 bits are used to select which bit to set in the given register

(with a value of 0 setting 0x8000_0000 and 31 setting 0x0000_0001).

Therefore, the example DA maps to bit 29 of register 1.

Low-order 5 bits of BR_CRC: LO_CRC = 0b11101 = 29

Therefore, GADDR1 is ORed with the value 0x0000_0004.

Additional calculated examples follow:

Example 1:

•Destination MAC address: DA = 01005E000128

•CRC remainder value: CRC = 0x821D6CD3

•Bit-reversed least-significant byte of CRC value: BR_CRC = 0xCB =

0b11001011

•High-order 3 bits of BR_CRC: HO_CRC = 0b110 = 6

•Low-order 5 bits of BR_CRC: LO_CRC = 0b01011 = 11

•GADDR6 = 0x0010_0000

Example 2:

•Destination MAC address: DA = 0004F0604F10

•CRC remainder value: CRC = 0x1F5A66B5

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