stupid questions about PASM2

Comments

• evanh Posts: 15,187

  2019-02-19 02:10

  I wish! It's the other way around.
  
• msrobots Posts: 3,704

  2019-02-19 02:54

  shhhh., I thought I read it somewhere,
  
  so after a RET I get the flags from the sub, right? What you mean by 'other way around'?
  
  Enjoy!
  
  Mike
• evanh Posts: 15,187

  2019-02-19 03:31

  I can't use _RET_ and have it preserve the calling flags so that conditional execution works across calls. I have to use RET WCZ instead.
  
• msrobots Posts: 3,704

  2019-02-19 05:11

  so _ret_ or RET will return the changed flags but RET WCZ will preserve them and restore the flags to the point of the call?
  
  curious,
  
  Mike
• Cluso99 Posts: 18,069

  2019-02-19 06:45

  There are two cases you need to consider.
  
  1. A subroutine wants to return any flags it changes to the calling routine.
  eg: on return I set/clear Z &/or C flags to pass results of the subroutine, so Z might be passed/success where NZ is fail/error
  
  2. A subroutine needs to use flags but the calling program does not want them changed.
  
  Both of these methods have their advantages and disadvantages.
  
  The P1 always uses 1. above. If 2. is required, then the subroutine needs to save the flags on entry, and restore them before returning.
  
  On the P2...
  1. works with
  _RET_ <opcode> <operands>
  and
  RET
  
  2. works only with
  RET {wc/wz/wcz} where the Z &/or C is preserved only if the modifier is used.
• msrobots Posts: 3,704

  2019-02-19 07:09

  thank you @Cluso99 that is a useful explanation.
  
  Enjoy!
  
  Mike