Running libsigrok master at 04a0e0dc1c6bfb7b80119795bb854e66e8abbd1a. With a Rigol DP821A connected, running sigrok-cli --scan causes the hpib-pps subdriver to probe the Rigol with "ID?". The Rigol doesn't recognise this, which leads to: sr: scpi_usbtmc: USBTMC bulk in transfer error: LIBUSB_ERROR_TIMEOUT. and the device beeping and displaying "Remote command is incorrect". This may be a trickier one to solve than #1272 because presumably old HP kit doesn't like the usually-safe *IDN? as a first query. Possible solutions: - If old HP kit will ignore *IDN? harmlessly, send that first and try ID? only if no reply is received. - Don't let hpib-pps scan anything recognised modern USB kit (e.g. Rigol VID) unless specifically directed to with a conn setting. - Don't scan hpib-pps at all without a conn setting?