Add tracing support via GPIOs to trace the basic state of the Ethernet
peripheral. The following signals are provided:
- One GPIO pin is toggled on entry of the Ethernet ISR
- On TX start an GPIO is set, on TX completion it is cleared
- On RX complete an GPIO is set, once this is passed to the upper layer
the GPIO is cleared again
In order to reduce the overhead, GPIO LL is used. By default the
on-board LEDs are used as tracing GPIOs. This makes it easy to debug
when the state machine gets stuck without the need to attach a scope or
logic analyzer.
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