The goal of this exercise is to get 1 KB of STACK memory space and separate it in two spaces, each one with 512 B. The first space will be pointed by MSP and the second will be pointed by PSP.
As such, when the processor is on Handler Mode, the first portion will be used as stack memory.
By consequence, when the processor is on Thread Mode, the second portion will be used as stack memory.
Exercise from Embedded Systems Programming on ARM Cortex-M3/M4 Processor