rosserial: node_handle hardware.read()

edit

It reads (bytes) from whatever is currently templated as being the "hardware" that rosserial uses for communication with the (ROS) host. It's a member variable of which the type depends on the Hardware template argument.

To make it more concrete: if the NodeHandle is specialised for an Arduino, it'll probably use the (first) serial port to read from / write to. If it were an embedded device that has an ethernet port, it'd probably be a TCP or UDP socket file handle. Etc, etc.

Edit:

So is this statement correct? The "hardware" is the Arduino?

Well, to be precise: hardware actually points to whatever the underlying platform uses to transmit and receive bytes. For Arduinos, that's typically:

• hardware RS232
• software RS232 (some pins)
• Serial-over-USB

See rosserial_arduino/src/ros_lib/ArduinoHardware.h for the Arduino "serial type" class and rosserial_arduino/src/ros_lib/ros.h for the Arduino specialisation of the rosserial template (note that it could use the serial and the TcpHardware types).

Edit 2:

And for example the uint32_t ms = hardware_.time(); function reads the clock from the Arduino and not from the host?

It's defined here, as a member of ArduinoHardware and calls millis(), so it would seem so, yes.