Unhandled R4300i OpCode at: 802800EC teq r0, a0 - HELP!!

[Clements]

The are only 3 valid extensions for N64 rom images, z64, v64 and n64:

z64 - Big Endian, non-byteswapped, generally preferred format
v64 - Byteswapped
n64 - Little Endian (least preferred format)

Non-interleaved formats are preferred over interleaved formats. The others (rom/usa/jap etc) are essentially meaningless, and are in truth one of the 3 main formats.

You can identify the byte order and convert between the three main formats en masse with Tool64. The byte order has nothing to do with whether a rom image is a bad dump or not like Smiff said.