Csound implements a software bus for internal routing or routing to external software calling the Csound API.
The opcodes to use the software bus are:
chn_k
chn_a
chn_S
chnget
chnset
chnsend
chnrecv
chnclear
chnexport
chnmix
chnparams
The invalue and outvalue can also be used for communication with the Csound API.