Original version by John Hay.
Simplified timestamp code by reading the time exactly when necessary.
This may slow down the interrupt handler with extra calls to microtime(),
but only in bad configurations - the input fifo should normally be
disabled if timestamps on input are being used, since otherwise the
timestamp won't be precisely associated with any particular input event.
The interrupt handler remains slowed down by one test and branch for
each input (and now DCD change) event - avoiding this is not practical
yet.
The simplifications also fixed:
- timestamps for input sometimes being clobbered by output and modem
status interrupts.
- valid timestamps not being available unless the port is configured with
vector siointrts. siointrts no longer exists.
- compiler warnings about siointr* in some configurations.
Simplified timestamp and probe code by depending on recent changes in
microtime() and DELAY() to preserve the interrupt enable flag.
7d64a7fe80