I used the ACR 122 before and it worked flawlessly with an Android < 4.1 phone. I used it to exchange P2P SNEP messsages... But since the phone got 4.1, the reader starts beeping and flashing when you place the phone above it. Does anyone else have found this incompatibility? Any solutions?
Since Android 4.1 Jelly Bean, NFC peer-to-peer communication is configured to use a higher bitrate (212 kbps), while earlier it was using 106 kbps (in Android devices that have Google Wallet installed it was always using 212 kbps).
I don't know whether the ACR122U can support the higher bitrate through javax.smartcardio. The NFC chip inside (NXP's PN532) can certainly do it. The low-level ISO18092/ECMA-340 protocol for 212 and 424 kbps is different from 106 kbps. With 106 kbps it uses the same modulation as ISO14443, while the higher bitrates use the same modulation as FeliCa (see page 7 and 8 of the standard). So I suspect this cannot be handled through javax.smartcardio.