Adruino and ARM Processor interfacing via JTAG

hi all,

I am looking into how I can make my own JTAG interface using an Adruino. I understand there are 4 pins in the ARM Processor for JTAG.

1) Does JTAG work during operation of device (hence a debugging tool)?
2) Can I simply connect the 4 JTAG pins to an adruino programmed to send and receive signal as accordance to the IEEE standard?
3) Will I need to power the ARM Processor or is there a separate power source for the JTAG logic?

Thanks to anyone reading this