How do I Experimentally determine MIPS (Million Instructions Per Second) of a Microcontroller like Arduino?

 

Welcome to AAC.

Why would you want to do this? It is not a useful benchmark since it doesn't reflect anything about real world applications.

 

1. Write a short program in assembler to output 1 to pin and then to output 0 to the same pin. It will probably be about 5 instructions long. It would look like this in ARM code
loop: MOVS R0,#1
STRB R0,[R3,pin]
MOVS R0,#0
STRB R0,[R3,pin]
B loop
2. Measure the output frequency (you can use an oscilloscope)
3. MIPS is number of instruction in the loop x output frequency divided by 1000000
As @Ya'akov says, it won't be that useful to know because in ARM code an STR instruction takes twice as long to execute as a MOV instruction.

 

That gives the speed in BogoMips.