[Nursie]

So the 'kernel' I wrote was not the one running on the card. 'In the Industry' (which sounds so pretentious!) the core of the EMV logic that runs on a terminal is often referred to as the kernel. It's not much like a real OS kernel!

The kernel I wrote in about 2002/3 was in C and allowed a PC using a dumb reader (with secure PIN pad) to run the transaction, on Windows, Linux or (shudder) Unixware at the time.

Years later in 2014 when I worked on a terminal product the company had bought in a third party kernel, also written in C to run on an embedded MIPs board. There was a platform SDK and a custom gcc variant to build bare-metal executables. You bootstrapped the kernel by passing it a malloc implementation and a couple of hooks to other things like accelerated crypto functions etc, and it provided an API to run the transaction.

I also worked briefly on a contactless terminal product in 2012, which IIRC was C and C++ (old-skool C-like C++) on a proprietary OS of some sort, and they were moving to embedded linux on ARM at the time.

(edit - See also rswall's parallel answer, it's very good. I wrote an EMV L2 kernel in that parlance, and interacted with another.)