TPMS used defined subroutine calls for screen functions from COBOL or PL / I, which in some users'eyes made it more difficult to use.
32.
During a subroutine call, the register stack moved up 32 words, so the caller's registers 32 47 became the called subroutine's registers 0 15.
33.
A subroutine call may also have random number function, available in many languages, that returns a different pseudo-random number each time it is called.
34.
More complex subroutine calls involve the use of the PREP instruction, which saves the return information in the first bytes of the current memory segment.
35.
Each subroutine call required its own set of registers, which in turn required more real estate on the CPU and more complexity in its design.
36.
A return retrieves the saved contents of the PC and places it back in the PC, resuming sequential execution with the instruction following the subroutine call.
37.
The ACE implemented subroutine calls, whereas the EDVAC did not, and the ACE also used " Abbreviated Computer Instructions, " an early form of programming language.
38.
Return-jump allowed simple subroutine calls and bank switching allowed other 4K banks of memory to be addressed, albeit clumsily, up to a total of 32, 768 words.
39.
Using BLWP / RTWP, it is possible to nest subroutine calls despite the absence of a stack, however, the programmer needs to assign the appropriate register workspace explicitly.
40.
This is due to the fact that message passing is essentially a subroutine call, but with three more additional overheads : dynamic memory allocation, parameter copying and dynamic dispatch.
