Computing stuff tied to the physical world

DHCP support

In AVR, Software on Jun 16, 2011 at 00:01

Not long ago, Andrew Lindsay added support for DHCP to his EtherShield library, which is derived from the same “Guido Socher & Pascal Stang” code base as the EtherCard library. Fantastic work, hats off!

I’ve reworked the code to simplify things, and more importantly: reduce its code size. Many of these changes made it into Andy’s Github code base, but I’ve decided to take it quite a bit further and completely redo the way DHCP gets called in sketches.

It’s now based on just one call: dhcpSetup(). For completeness, I must mention that lease expiry and re-lease have been swept under the rug for now. Here’s the new testDHCP.pde demo I’ve come up with:

Screen Shot 2011 06 16 at 00.10.07

Sample output:

Screen Shot 2011 06 08 at 13.43.27

The entire demo sketch is currently 7732 bytes (6420 without the serial I/O). The DHCP part appears to require about 1200 bytes in all this. Note that the actual code to perform or serve web requests will add several more Kb to the total size, this merely illustrates the minimal code for doing DHCP.

There’s a “#define SELECT_BIT” in the enc28j60.cpp source which can be changed for boards which don’t use B0 (i.e. arduino digital I/O pin 8) as chip select. There’s also a “#define FULL_SPEED” setting which switches the SPI bus to 8 MHz during block transfers – it’s enabled by default and has a noticeable impact on performance.

So now any ENC28J60-based EtherCard with an ATmega328 can be connected to a local LAN and become usable as web server and/or client without having to configure an IP address, DNS server, or gateway!