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Smallest IP Target Device?
Donimo asks: "I have seen many tiny ethernet loopback jacks and keyfobs, and I'm looking for the smallest IP equivalent for my toolkit. It just needs to plug into an RJ45 ethernet port and respond to ping. If the IP address is configurable, so much the better. I have looked at small IP print servers, and I could probably knock one up from a Gumstix but these are comparatively expensive solutions. Any ideas?"
I have seen PIC microchips connected to something like an RL8139AS or cs8900, PHY and jack. The pic16xxx is the simplest device that can do the ICMP/IP and have enough pins to talk to the ethernet chip. The atmel devices are alternatives, like the attiny maybe. These chips are sub-$1, but remember the ethernet chip is at LEAST $10. Under $20 devices are possible where they have dedicated IP addresses and can send/receive UDP, raw IP and simple ICMP like ping. TCP will require more complexity and ram. Linux is way too big if youre talking about the simplest devices... other RTOSes fill that niche if you intend to have full TCPIP. In that case, look at micrium ucos, ecos, freertos and other similar devices.
Will be interesting to see if someone can use a fast 8-bit chip to act as an ethernet chip too (bitbanging ethernet). Will have to be well over 10MHz and should be able to do ARP first. In that case, sub-$5 devices are possible with chips with fewer pins, with the BOM quite possibly under $2 (jacks, chip, board, phy in qty). But these will be far less reliable.
"Give orange me give eat orange me eat orange give me eat orange give me you." -Nim Chimpsky
XPort product page with lots of marketing spiel
You won't run Linux on it, because it's a 16-bit 8086 clone inside with 256kB RAM and 512kB flash, but if you want something to provide a quick-and-easy ethernet interface to a piece of development hardware, it's ideal. I suspect it may be a bit expensive, though (no prices available).
There are some other similar devices from the same manufacturer --- among them is the WiPort, which is much the same thing as the XPort but uses 802.11b...