TuneTracker Systems has kindly donated a new serial port driver to Haiku's community. The driver was commissioned by TT Systems and developed by François Revol, aka mmu_man, aka kungfu-coder (let's see if this one sticks) and works well with a series of serial (ah!) cards by Manhattan.
The code has already been commited to the repository and should be included to the build images soon. Good news.