DS80C400_03 Datasheet, PDF (73/96 Pages) Maxim Integrated Products – Network Microcontroller

Figure 14. NetBoot Code Flow Chart
NETBOOT
INITIALIZATION CODE
ACQUIRE MAC
ADDRESS FROM DS2502
1-WIRE DEVICE
Y
WITH IP
ADDRESS
N
DHCP
DS80C400 Network Microcontroller
NetBoot PROCESS
GET IP ADDRESS FROM
1-WIRE DEVICE
TFTP/FLASH WRITE
FIND USER CODE
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
1Dh 54h,49h,4Eh,49h Address(4) Gateway(4) PrefixLength(1) TFTP Server Address(16) Checksum(2)
ëTINIí
29 (LENGTH)
IPv4
IPv4
IPV4
(BYTE
CONVERTED TO
SUBNET MASK)
IPv4 or IPv6
1íS COMPLEMENT
OF CRC-16 (LSB
FIRST)
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 ìnext server IPî field. Because some DHCP servers do not allow configuration of the ìnext
server IPî 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 ìnext
server IPî field.
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