This is the processor used in the iPhone 3GS.
S5L8920 and derivative SoCs use the armv7 family, with later versions of the architecture using armv7f/armv7s.
S5L8920 using THUMB-2 instruction set as well as ARM and THUMB ones. Binaries included in iOS are compiled for only ARMv7 and are not compatible with older CPUs.
Bootrom Version: Bootrom 359.3