I haven't used my Irix based O2 in years, so I haven't even tried to maintain irix-dtrrts and don't have any copies available either.
Originally I wrote irix-dtrrts for Irix 6.2 so my O2 could communicate with an X10 Firecracker which I received as part of a bundle through a promotional offer. At the time Irix couldn't control the DTR and RTS lines of an RS-232 port as were need to signal the Firecracker, so I wrote a small in-kernel device driver for Irix 6.2 to perform the DTR and RTS signalling as required by bottlerocket, the command line program used on UNIX systems to control Firecrackers.
I seriously doubt that irx-dtrrts would work on Irix 6.5 or later. I certainly haven't tried. :-)