Serial connection to the board is possible via the JTAG header, see e.g. for NS2. This allows interrupting the boot sequence, unlike netconsole.
You need to be aware that the serial port voltage level is 3.3 V, so you either need level converter or cable designed for 3.3 V operation. This page gives you several USB-to-serial options which run at 3.3 V. Usually, however, the VCC is directly from the USB bus and is +5 V.
<note important>Do not connect VCC, only RX, TX and GND pins!</note>
Now when you boot up your device, the output is similar to what you see on netconsole. In addition, you get input capability (e.g. to interrupt boot).