> I'm trying to setup Midas with the Caen vx2740 VME digitizer board.

welcome to the world of daq and midas! Ben already answered and he will help you with this specific hardware. (we work together)

> #0  0x00005555555c2ee1 in rpc_register_function (id=id@entry=18000, func=func@entry=0x5555555a2790 <jrpc_helper(int, void**)>)
>     at /home/astrocent/workspace/packages/midas/src/midas.cxx:11947

I look at this line in midas and I do not see any problems other than all functions that touch rpc_list are not thread safe,
and calling them at the same time as rpc calls are active will cause memory corruption and crash. This is not a problem
in most programs because rpc_register_function() is usually called once at the beginning of everything, before any RPCs
are received, sent or processed. I filed a bug against this problem. https://bitbucket.org/tmidas/midas/issues/362/rpc_list-is-not-thread-safe

> with is "jrpc"?

I implemented it years ago to allow web pages to call mhttpd (XHR/HTTP) to call user frontends (MIDAS RPC) to perform real-time actions,
i.e. to turn power supplied on or off. "j" stands for "json", but most experiments send very simple commands
and do not use json encoding.

K.O.