If the destination register bank implements the register_view interface, then this is used by the set-device-reg command to write register. Otherwise the set-device-reg command performs an inquiry write, typically not overwriting read-only data in the device. The write-device-reg command always does a standard write access. Note that not all device models support inquiry accesses.
The field parameter can be specified to update a register field. One can use the print-device-reg-info command to see which fields a register has.
The -l or -b flags are used to specify in what byte order data should be interpreted. The default is to interpret data as little-endian, except if a bank has explicitly declared big-endian as its preferred byte order (which can happen for devices written in DML).