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DS80C400 Network Microcontroller
73 of 96
Figure 14. NetBoot Code Flow Chart
Next, the TINI400 ROM searches the 1-Wire bus for an external device (separate from the device containing the
MAC address) that contains an IP address and TFTP server IP address. In order to correctly acquire the IP and
TFTP server addresses from an external 1-Wire device, the data read from the device must conform to a specific
format. This format is shown in
Figure 15
.
Figure 15. 1-Wire IP and TFTP Server IP Address Format
If the IP and TFTP server addresses cannot be acquired from a 1-Wire device, the NetBoot process uses DHCP to
get this information. The DS80C400 broadcasts its MAC address in a DHCP Discover packet. A DHCP server, if
available, should then respond with an IP address offering. The DS80C400 subsequently requests the IP address,
to which the DHCP server must acknowledge. In the DHCP acknowledge packet, the TFTP server IP address is
then read from the “next server IP” field. Because some DHCP servers do not allow configuration of the “next
server IP” field, the DS80C400 recognizes the site-specific option 150 (also used on Cisco IP phones to get TFTP
server IP addresses). When option 150 is present in the acknowledge packet, it will take precedence over the “next
server IP” field.
IPv4 or IPv6
IPv4
IPv4
‘TINI’
1Dh 54h,49h,4Eh,49h Address(4) Gateway(4) PrefixLength(1) TFTP Server Address(16) Checksum(2)
1’S COMPLEMENT
OF CRC-16 (LSB
FIRST)
29 (LENGTH)
IPV4
(BYTE
CONVERTED TO
SUBNET MASK)
NETBOOT
INITIALIZATION CODE
ACQUIRE MAC
ADDRESS FROM DS2502
1-WIRE DEVICE
WITH IP
ADDRESS
FIND USER CODE
TFTP/FLASH WRITE
DHCP
GET IP ADDRESS FROM
1-WIRE DEVICE
NetBoot PROCESS
Y
N
Содержание DS80C400
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