How long should I wait for a link up state?(W6100)

Question

I am developing a device which can be connected to Ethernet, but can also be used autonomously using its integrated rechargeable battery. Since the Wiznet chips use way too much power to keep them running while we are on battery alone, I am cyclically switching the chip on, look for a link and then switch it off again. Now the question is how long does the chip need to detect/reach a link up state? Since automatic MDI-X is on, I took the maximum of 1,4s for that from wikipedia and rounded up to 1,5s https://en.wikipedia.org/wiki/Medium-dependent_interface Does that make sense or do I need to wait longer (or can I keep it on for a shorter time?)

Lihan__ · Answer

The W6100’s internal PHY begins operating in Auto-Negotiation and Auto-MDIX mode immediately upon power-up, so as soon as a cable is plugged in it will start link negotiation without any additional configuration. Choosing a timeout of 1.4–1.5 seconds is reasonable as a conservative figure, since it covers the maximum 1.4 s asynchronous Auto-MDIX timer plus the chip’s boot and link-pulse-detection time. However, factors like cable length and quality, the switch or hub PHY’s response speed, temperature and power-supply stability, and EMI can all influence how long link-up actually takes in the field. We therefore recommend thorough testing in your target environment to determine the optimal timeout—and, if needed, adding a 10–20 % safety margin to your measured values.