Hi i am using a class 10 kingston micro sd with adaptor in my 2ds and i havent had any problems, not sure what the speed difference between class 10 and class 4 no harm in trying it.
Try going back through the guide step by step starting from when you needed to downgrade to 2.1 you need to get the two otp files before you can continue.
No problem will try and help i only done this process saturday just gone so its still pretty fresh in the memory.
You shouldnt be trying to use gamecarts at all on 2.1 so i would stay clear of that.
I was a complete noob before i seen this guide if you follow the guide step by step you shouldnt have a problem. It took me about 4-5 hours of carefully reading the guide and doing the appropriate functions on my 2ds the link suggested by sToOz was the one i used aswell.
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So as of right...
I have succesfully applied arm9 to my 2ds i have a couple of questions
1. Is it safe to update my ds when nintendo release new updates?
2. If i want to use a bigger sd card can i just transfer the files from my current memory card to the new one without loss of functionality.
Thanks in advance...