EJTAG ID Codes and Implementation Registers
When an EJTAG system is reset, the data register is automatically filled with the result of an IDCODE instruction. This code usually includes the processor and the manufacturer, although it is not a standard. The important part of the IDCODE is using it to determine if your host hardware is communicating with your target. Whether or not the host speaks fluent jtag, if it can navigate to the data register and shift out the contents, one can see if the electrical connection is sound.
IDCODEs WT54GLv1.1 : WRT54Gv8 : WRT350Nv1.0 : 0x0478517F
The implementation code instruction returns an indication of features on the particular platform. Below is the information from the MIPS EJTAG Specification, document #MD00047.