1 Mutual agreement

1.1 Caller side

• if there are arguments:
  • arguments are pushed in reverse order
  • on TTP, arguments are pushed contiguously (no gaps between them)
  • this implies the last argument has the highest address
• the return address (the address of the instruction right after the jump to the callee) is pushed after all the arguments (if any)
• jump to the entry point of the callee
• the callee should return to the instruction right after the jump instruction
• if the callee returns a scalar value:
  • the return value is assumed to be in register A
• the value of registers A, B and C are not assumed preserved
• if there are arguments:
  • the caller has the responsibility to clean up the stack space used by arguments, if any

1.2 Callee side

• at the entry point of the callee:
  • the stack pointer points to the return address
  • if there are parameters:
    • the first parameter starts at the address immediately after (higher than) that of the return address
    • the last parameter has the highest address
    • parameters are contiguous in TTP
• in the callee’s code:
  • additional stack space may be utilized
  • there is no need to preserve the values of registers A, B, or C
• at the exit point of the callee:
  • if the callee has a scalar return value:
    • use register A to store the return value
  • the callee is responsible to pop the return address
  • the callee uses the popped return address to return to the caller