this works on cs4630 chips, and should implement the clkrun hack for
thinkpads- this will display diagnostic messages when triggered until its
correctness is established.
then invoke the children. As the value of HISR can be read
only once, pass the HISR to the children via struct
csa_bridgeinfo, stored in the ivars of them.
- Clear the contents of serial FIFO upon stopping the DMA for
playing. This may eliminate buzz on playing. Experimental.
