multiplexing serial communications
rtfps0 at isa? port 0x1230 irq 10
com* at rtfps?
rtfps driver provides support for IBM
RT PC boards that multiplex together up to four EIA RS-232C (CCITT V.28) or
RS-422A communications interfaces.
rtfps device is the master device for
up to four
com devices. The kernel configuration
com devices as slave devices of the
rtfps device, as shown in
port specification for the
rtfps device is used to compute the base addresses
com(4), intro(4), isa(4)
rtfps driver was written by
Charles Hannum, based on the
rtfps driver is unlikely to work on
non-EISA and non-PCI machines. The ISA bus only asserts 10 I/O address
lines, and this is not enough.
Even on EISA and PCI machines, some address conflicts have been observed. On one machine, the second port always conflicted with something (though it's not clear what) and caused strange results. Disabling the second port in the kernel config allowed the other three ports to function correctly.