In turbo-geth RPC calls are extracted out of the main binary into a separate daemon. This daemon can use both local or remote DBs. That means, that this RPC daemon doesn't have to be running on the same machine as the main turbo-geth binary or it can run from a snapshot of a database for read-only calls. Docs
For local DB
> make rpcdaemon
> ./build/bin/rpcdaemon --chaindata ~/Library/TurboGeth/tg/chaindata --http.api=eth,debug
For remote DB
Run turbo-geth in one terminal window
> ./build/bin/tg --private.api.addr=localhost:9090
Run RPC daemon
> ./build/bin/rpcdaemon --private.api.addr=localhost:9090
Try eth_blockNumber call. In another console/tab, use curl to make RPC call:
curl -X POST -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_blockNumber", "params": [], "id":1}' localhost:8545
It should return something like this (depending on how far your turbo-geth node has synced):
{"jsonrpc":"2.0","id":1,"result":823909}