irq_unexpected_isr: ERROR irq: 3
...
My guess is that AN external IRQ is triggered (possibly not the PHY IRQ) but the ISR handler for that one is not ready yet. I will add debug messages.
IRQ 3 is a Hardfault, not an external IRQ or peripheral interrupt.
I would expect that situation to be a simple NOP, but it seems that undefined handlers are set to this function "irq_unexpected_isr"
Initially all interrupts vector to irq_unexpected_isr() but that is fixed early in irq_initialize() when the hard fault handler is attached to IRQ 2. Prior to that, the hard fault would be given to irq_unexpected_isr(), although I don't think the serial driver has been initialized at that point either.
