> Boot PROM Selftest
> 
> PROM Checksum Test
> Context Reg Test
> Segment Map Wr/Rd Test
> Segment Map Address Test
> Page Map Test
> Boot PROM Selftest
> 
> PROM Checksum Test
> Context Reg Test
> ...

I have seen this sort of looping selftest when there was a modem, with
command echo turned on, connected to the other tty port.  Apparently
the selftest output goes to both tty ports, and when it is looped back
the test keeps restarting.