Referring to http://excamera.com/sphinx/gameduino2/ and http://cdn.sparkfun.com/datasheets/Dev/Arduino/Shields/MP3%20Shield-v13.pdf
There are several pins that are attempting being used by both shields.
refer to http://www.billporter.info/forum/topic/host-running-less-than-16mhz/#post-3309 they had similiar pin conflicts
Gameduino2
11inSPI MOSI
12outSPI MISO
13inSPI SCK
8inGPU SEL*
9inSD SEL*
2outINTERRUPT*
A2outACCEL_Z
A1outACCEL_Y
A0outACCEL_X
vs the SFEMP3Shield
2 out MP3-DREQ*
3 in MIDI RX
4 in GPIO1
6 in MP3-CS
7 in MP3-DCS
8 in MP3-RST*
9 in SD-CS*
11inSPI MOSI
12outSPI MISO
13inSPI SCK
it is OK for MOSI,MISO and SCK to share.
But rest 2, 8 and 9 are problems you will need to over come.
In this case:
Both shields are Wired to use INT0 on D2. The MP3 uses it as an interrupt. Not sure if the G2 does. Its code is very extensive. and I see it is not well documented as to changing its pins.
Refer to https://www.youtube.com/watch?v=behMgV3tUr4 it explains how to move pins. Also refer to http://www.freetronics.com.au/pages/stacking-arduino-shields.
The SFEMP3 has all its pins defined in the SFEMP3ShieldConfig.h. You can easily specify any changes you make.
I would move the SFEMP3’s D2 to D3. Then make sure that SJ2 is open. MIDI-RX is not needed and we don’t want it to interfere. Then move SD-CS from D9 to D10 and move MP3-RST from D8 to A3.
Then update SFEMP3ShieldConfig.h correspondingly. That should remove any conflicts.
