Apple Pay Suica on A12 Bionic iPhone XS/XR is different from other devices because basic FeliCa transactions bypass iOS and go directly to the Secure Enclave. You can see this in action with Express Transit power reserve, but if you observe carefully you can catch it in other ways.
I caught a glimpse today buying ice coffee at a JR station NewDays shop (supplied by Doutor btw). I was recharging Suica with Apple Pay and forgot it was still processing when I touched iPhone XS to the reader. The payment went through without a problem, the recharge completed a few seconds later.
Is this a iOS 12.4 beta thing or did A12 Bionic iPhone do this all along? I suspect it did all along and makes sense: the payment transaction bypassed iOS which was busy processing the Apple Pay recharge and wasn’t ready to post a balance update to the Secure Enclave. Prepaid and postpay processing at the same time…very interesting.
Most people think all Express Transit is the same, but Suica Express Transit prepaid is very different from EMV Express Transit postpay. Suica settles the transit bill in less than 200 milliseconds (ms) locally right at the transit gate, while EMV Express Transit leisurely (500 ms) tells the gate, ‘I am bank card XXX, put it on the bill’ for settlement later between the bank and the transit agency. For EMV there is a lot of backend system work to make that happen, and even then the user sometimes has to tap twice: