Summary
In this chapter, we’ve extended our knowledge of the ARM beyond the basic data-processing instructions we encountered in the previous chapter.
We began with the ARM’s register set, which is different from almost every other processor. RISC processors generally have 32 general-purpose registers. The ARM has only 16 registers.
Two of the ARM’s registers have a special purpose. Register r14 is called a link register and is used by the branch with link instructions to restore return addresses. Otherwise, it is a general-purpose register. Register r15 is the program counter, and that is very unusual indeed. This makes the ARM a very interesting device because you can change the program counter by operating on r15.
We also looked at shifting operations. Shifting simply involves bits moving one or more places left or right. However, as bits are in registers or memory locations, a shift involves bits moving into one and dropping out the other. The different...