Both iPhone and Watch ship with a Secure Enclave processor. Both are also H11-class SoCs. As such, there are broad similarities between the different blocks. Embedded cores present on-die use firmware written with RTKit, which is Apple's own broadly-used RTOS on cores codenamed Chinook. The codename for the eSIM platform on both the iPhone and Watch is Vinyl. The NFC (+Apple Pay?) controller is named Stockholm, and the Apple Watch Series 4 + iPhone Xs and Xr ship with version 5.
