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Showing posts from December, 2015

Ethernet Funnies

Sometimes it is very hard to connect to an embedded system, because the designers cut some corners to simplify the system and keep memory use down, or simply because the system is prehistoric and full of bugs. One such device worked fine provided that there was a little ethernet switch between the laptop machine and the target, but a direct connection between the laptop machine and target device only worked about half the time.  Even the little switch sometimes could not connect. MAC, PHY, MAG An ethernet interface device consists of three main parts: The Media Access Controller (MAC), the Physical Interface (PHY) and a set of transformers - the Magnetics.  When you plug a cable in, the PHY sends out little pulses to figure out what is going on and then swaps the wires around internally and changes the speed and duplex settings to make the interface work. The trouble was that the target only supports 100 Mbps, while the laptop machine wanted to run at 1 Gbps and the two just c