i currently have the new firmware 1.2.1. can I go back to firmware 1.0,9 or do I have to flash the sd card?
When I went back from 1.1 to 1.09 I needed to reflash the card. To get a clean install I recommend you buy a new sd card. I had problems and the only way to do a clean reflash was a new card. For $10ish is great insurance.
You can use a new card or just download sdformatter and format the card before flashing. If you really want to be thorough you can delete the partion first…