• HOME
• FORUM
• SEARCH
• CONTACT

• HOME
• 5. Advanced Topics
• Multiply Instructions
• Load/Store Multiple Instructions
  • Basics
  • Examples
• The Stack
  • The Basics
  • Stack Types and Instructions
• Subroutines
  • The Basics
  • Nested subroutines
• The Reset Pin

Nested subroutines

The BL instruction always uses r14 to store the return address. This leads to a potential problem if one subroutine calls a further subroutine - how will the program find its way back to the original call?

There is also a second problem in that there are only so many registers available. The main program may have stored valuable information in some of the registers, but the subroutine (or its writer) won't necessarily know which registers are used or may need to use those registers for its own computations.

The solution to both these problems is to use a stack to preserve the value of the return address and the contents of any other registers.