Maxim Integrated 78Q8430 Software Driver - Manual (Page 32)

78Q8430 Software Driver Development Guidelines UG_8430_004
Table 6: ICMP Frame Contents
MAC Header IP Header . . .
Dest.
Addr.
Src.
Addr.
Len/Type
1
Ver /
IHL
2
TOS Total Len Identification Flags /
Frag Offset
TTL Prot.
3
6 bytes 6 bytes 08 00 45 ?? 2 bytes 2 bytes 2 bytes 1 byte 01
304 308 30C 310 314 318
. . . IP Header, cont. ICMP Header
Checksum Src. Address Dest. Address
4
Type
5
Code
6
Checksum
2 bytes 4 bytes 4 bytes 0? 00 2 bytes
31C 320 324 328 – 2 LSBs
1 Type = 0x0800 indicates that an IP header follows.
2
Based on the IHL value, there may be extra data at the end of the IP header before the ICMP header.
3
The Protocol field is always 0x01 for an ICMP frame.
4
The driver should verify that the Dest. Address belongs to it.
5
A Type value of 0x08 indicates an ICMP echo request and 0x00 indicates an ICMP echo reply.
6 The Code value should always be 0x00.
This procedure is only suitable for IP packets that have not been fragmented. When the MF flag is clear
and the fragment offset value is zero, there are no fragments. This is the case when the last 14 bits of
the Flags/Frag Offset field in the IP Header are all zeros.
Enable ICMP Classification
Use the following procedure to enable the identification of ICMP echo requests in the CAM:
STEP 1: Change the offset field of CAM rule 0x24 from 0x00 to 0x05.
• Set the CAR ADDR field to 0x24
• Change the RCR Byte Offset field to 0x05. This causes the next byte looked at by the
classification engine to be the Flags and MSbs of the Fragment Offset.
STEP 2: Set CAM rule 0x7B to verify the MF flag is clear and the fragment offset MSbs are
zero.
Reg. Field Value to write
CAR ADDR 0x7B
Data Match 0x00
Data Mask 0x3F
Previous Hit Match 0x24
RMR
Previous Hit Mask 0x7F
Byte Offset Retain default: 0x00
Interrupt Retain default: 0
Control Logic Action NOP
RCR
Match Control MD
STEP 3: Set CAM rule 0x7A to verify the fragment offset LSbs are all zero.
Reg. Field Value to write
CAR ADDR 0x7A
RMR Data Match 0x00
32 Rev. 1.0