Comment 5 for bug 588748

> Can you add some debugging to see what IER is being set to?

With DEBUG_SERIAL defined, serial logs:
serial: event 2
serial: write addr=0x01 val=0x02
serial: read addr=0x01 val=0x02
serial: read addr=0x02 val=0x02
serial: write addr=0x01 val=0x00
serial: write addr=0x03 val=0x80
serial: write addr=0x00 val=0x0c
serial: write addr=0x01 val=0x00
serial: write addr=0x03 val=0x03
serial: write addr=0x04 val=0x0b
serial: read addr=0x05 val=0x60
serial: read addr=0x06 val=0xb0
serial: read addr=0x00 val=0x00
serial: write addr=0x01 val=0x0f
serial: read addr=0x02 val=0x02
serial: read addr=0x02 val=0x01
(stalls here)