I want to connect an ATMEGA328P to a mobile phone, a Samsung Galaxy S3 to interface some data.
I need to use the microSD port behind the battery cover for this purpose, so here is the question, Is it possible to use SPI to emulate an SDIO card, or even an MMC card if I hook up the ATMEGA328P via SPI to the microSD slot on the back of the Samsung Galaxy S3? If so, how can I wire it up and which modes are suitable? What is the difference between MMC, SD, SDIO. Can all of them be used without some kind of license? What voltage can I expect? Will the ATMEGA328P be runnable on both 1.8v and 3.3v?
EDIT: This question is really about MMC/SDIO and not looking for different solution. There are companies manufacturing MicroSDIO cards with NFC functionality and ZigBee functionalities and I have read multiple users who had no problem getting these to work on Android, so my guess is that they either emulate a memory card and read/write to files or if there is actually a possibility to develop user land drivers, or they have rooted their device and made changes in the system. But since there are companies advertising these products i am doubtful they require root access. From what I read SDIO should be supported in the kernel since Android 2.2 but the online information on this I have found is very limited. If SDIO is supported I would still expect there to be support for user land drivers. If it is the case that SDIO mode on Android need drivers in the system image I would appreciate a reference on this and how to accomplish it.
I would have no problem making this work using Android open accessory protocol, USB OTG, Bluetooth LE (Smart) or WiFi, with all these I can write user land "drivers". I have no experience in SDIO and that is why I am asking the question here I realize that my original question was not clear enough on this point.
I am interested if someone have real experience in this and suggestions of other solutions will unfortunately not help me at this point. Thanks for your understanding