Doc updates

README.md

@@ -449,11 +449,12 @@ implementation may not actually affect power use. To use it, implement the
 `VintageNet.PowerManager` behaviour and register the implementation in your
 `config.exs`.
 
-Additionally, if VintageNet is not having any luck with a network interface, it
-may invoke power management to turn the network interface off and on. How this
-works is dependent on the power management implementation. The VintageNet power
-management code supports mandatory minimum on and off times to prevent damage to
-hardware and also minimize pointless power cycling of hardware.
+Additionally, VintageNet runs a watchdog-like service for network devices that
+supply `VintageNet.PowerManager` implementations. If the watchdog is not pet
+within the timeout period (user-specified and defaults to 60 seconds),
+VintageNet powers the device off and and on. The VintageNet power management
+code supports mandatory minimum on and off times to prevent damage to hardware
+and also minimize pointless power cycling of hardware.
 
 While many network devices are fairly reliable and powering off and on seems
 unnecessary, it can save a trip to the field or a full device reboot.

docs/cookbook.md

@@ -354,4 +354,11 @@ Then add the following to your `config.exs`:
 config :vintage_net, power_managers: [{MyPowerManager, ifname: "wlan0"}]
 ```
 
+VintageNet determines whether devices are ok by use of a watchdog. VintageNet
+and its technology implementations pet the watchdog by calling
+`VintageNet.PowerManager.PMControl.pet_watchdog/1`. This may be insufficient for
+your application. Options include calling that function in your code regularly
+or modifying the `:watchdog_timeout` in the power manager spec in your
+`config.exs`.
+
 See `VintageNet.PowerManager` for details.