SIGIO on a udp socket - how should I do? (4.3BSD)

[Akira Takiguchi]

     I'm writing an application which use sunrpc[udp] for interprocess
communication.  Since I need asynchronous processing, I tried to set
FASYNC flag on the udp socket but no SIGIO seems to be delivered when
request arrives.  Is there something I should do to get SIGIO properly?

     I'm on a MIPS RS3230 with RISC/OS 4.51, bsd43 world.

     Thanks in advance,  (No email, please;  sorry for inconvenience)
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