From The Apple Wiki
Samsung S5L8443
Application Processor
Designed bySamsung

The Samsung S5L8443 is a system-on-a-chip used in the iPod shuffle (4th generation). It is found in a package-on-package (PoP) configuration with DRAM and NAND flash stacked on top of the CPU core.

While the chip's existence isn't well documented, the image headers contained in firmware files of this iPod shuffle points to its existence.