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Method 1 provides the fastest mechanism to obtain link state since it does not require communication with the physical layer device. For most applications, this mechanism is suitable and if necessary, the polling rate can be increased by calling NetIF_CfgPhyLinkPeriod(). In order to utilize Method 1, the application may call NetIF_LinkStateGet() which returns NET_IF_LINK_UP or NET_IF_LINK_DOWN.
The accuracy of Method 1 can be improved by using a physical layer device and driver combination that supports link state change interrupts. In this circumstance, the value of the global variable containing the link state is updated immediately following a link state change. Therefore, the polling rate can be reduced further if desired and a call to NetIF_LinkStateGet() will return the actual link state.
Method 2 requires the application to call NetIF_IO_Ctrl() with the option parameter set to either NET_IF_IO_CTRL_LINK_STATE_GET or NET_IF_IO_CTRL_LINK_STATE_GET_INFO.
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Calling NetIF_IO_Ctrl() will poll the hardware for the current link state. Alternatively, NetIF_LinkStateGet() gets the approximate link state by reading the interface link state flag. Polling the Ethernet hardware for link state takes significantly longer due to the speed and latency of the MII bus. Consequently, it may not be desirable to poll the hardware in a tight loop. Reading the interface flag is fast, but the flag is only periodically updated by the Net IF every 250mS (default) when using the generic Ethernet PHY driver. PHY drivers that implement link state change interrupts may change the value of the interface flag immediately upon link state change detection. In this scenario, calling NetIF_LinkStateGet() is ideal for these interfaces.
Wait until
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the cable is connected (Link up)
Sometime the application might want to wait until the link is up before starting doing things on the network. The function NetIF_LinkStateWaitUntilUp() can be use to do such functionality.
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µC/TCP-IP stack offers two API functions : NetIF_LinkStateSubscribe(), NetIF_LinkStateUnsubscribe(), allowing the customer application to implement a callback function that will be called when a link state change occurs.
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The application may increase the µC/TCP-IP link state polling rate by calling NetIF_CfgPhyLinkPeriod(). The default value is 250ms.
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