8.3. When I compile a kernel with multi-port serial code, it tells me that only the first port is probed and the rest skipped due to interrupt conflicts. How do I fix this?

The problem here is that FreeBSD has code built-in to keep the kernel from getting trashed due t hardware or software conflicts. The way to fix this is to leave out the IRQ settings on other ports besides the first. Here is a example:

#
# Multiport high-speed serial line - 16550 UARTS
#
device    sio2    at isa? port 0x2a0 tty irq 5 flags 0x501 vector siointr
device    sio3    at isa? port 0x2a8 tty flags 0x501 vector siointr 
device    sio4    at isa? port 0x2b0 tty flags 0x501 vector siointr
device    sio5    at isa? port 0x2b8 tty flags 0x501 vector siointr