...continued from previous post.

OK, Dynamic Host Configuration Protocol - DHCP.
DHCP is used to automatically configure a networkdevice without actually knowing anything about the network it's attached to. There are hundreds and hundreds of pages to read about how it works so I won't cover it in much detials, just give a basic overview.


The process starts with the client sending out what's called a DHCP Discover message. This is sent as a brodcast message meaning it's addressed to any and all DHCP servers on the current subnet. One, or more, servers(s) will respond with a DHCP Offer message containing an offer for a lease of a specific IP adress for a specific amount of time. The client can then selects one of these offers and sends a DHCP request message, still as a broadcast message but it has now filled in the server it wants to use in a specific field in the message. If everything goes well the server responds with a DHCP Ack message meaning that it has now reserved the IP-adress for the amount of time specified and the client is free to use it. The client is NOT allowed to start using the IP-adress untill a valid DHCP Ack message is received. Along with the IP adress the server also provides other important setting such as the netmask and the gateway adress.

Like I said, this is just the basic outline of the process - there are alot of details to get into, which we don't have to do right now.


The DHCP implementation for the W5100/PBP3 is supplied as three files. The main file to include in your project is DHCP.pbp It's also in this file that a change or two may be needed. At the top, you'll find this:
Code:
HostNameLength          CON     6           ' <- Change this to match the length of the name.
HostName                VAR     BYTE[HostNameLength]
HostName[0] = "A"
HostName[1] = "m"
HostName[2] = "i"
HostName[3] = "c"
HostName[4] = "u"
HostName[5] = "s"
This is the host name that is supplied to DHCP server. It then (if it has the functionallity) passes it on the DNS server and the end-result is that the client device can be accessed by name, ie you can browse to http://amicus instead of trying to remeber the IP-adress. What you need to change is the HostNameLenght so that it matches exactly the lenght of the array containing the name you want to use. As in the example above the name is 6 bytes long therefor HostNameLenght is 6.

The DHCP.pbp file then includes two more files, DHCP_subs.pbp and DHCP_defs.pbp - neither of which 'should' need any editing for normal use.

As with the main "driver" files for the W5100 I've added a while bunch of debug-messages to the DHCP code. These can be enabled by adding a #DEFINE DHCP_DEBUG_LEVEL 1 or #DEFINE DHCP_DEBUG_LEVEL 2 to the application. Again, these adds quite a bit of code.

When the DHCP process is complete we can get the network setting to use from the arrays DHCP_IP, DHCP_NetMask and DHCP_GateWay and use these to initilise the W5100.

To be continued in the next post....