not pre-load the chip's Tx buffer, but instead waits for the Tx Ready
interrupt to transmit the first chunk of data.
* On the IOP310, set COM_HW_NO_TXPRELOAD, rather than COM_HW_TXFIFO_DISABLE.
This solves the "UART hangs" problem on the Npwr in a nicer way (i.e. we
get to use the FIFO, whee). The COM_HW_NO_TXPRELOAD happens to match the
Linux 16550 driver's Tx algorithm, and the "UART hang" was never observed
on the Npwr running Linux.
Eventually, we might want to eliminate the COM_HW_NO_TXPRELOAD, and simply
always use its algorithm. But it should be tested on more 16x50 variants
before we do that.
Kudos to Valeriy Ushakov <uwe@netbsd.org> for pointing out this solution
(which also happens to fix the stray UART interrupt issue on the Krups
Javastation), and to Allen Briggs <briggs@netbsd.org> for experimenting
with various methods of fixing this.
ff7306cf44