Nesting subroutines

[ercotronic]

Hi all,
is it possible (and correct)to nest subroutines using a 'then ' statment as in the 'i/o' section of code below)
e.g.
loop:
gosub i2clock 'get time
gosub i2 display 'display time
gosub i/o 'check pins
let b13 = 253 'load a test value
gosub keya 'to check keypad
if b13 <> 253 then keyb 'against
goto loop
end
i2clock:
"clock stuff here"
return
i2disp:
"lcd stuff here"
return
i/o: 'check for change of
if pin1 = 1 and $50 = 0 then delrc ' state
if pin1 = 0 and $50 = 1 then delro ' test
return

delrc
pause 50
if pin 1 = 0 then loop
let b0 = 1
peek $50,b0
gosub i2clock 'get time
gosub i2eewrite 'log time
gosub eeverif 'check if logged ok
return
many thanks for any input.

 

[ercotronic]

hi,
just realised that Hippy may have aleady answered my question in the "if/then with a gosub " topic below, but i would like to use gosubs to keep the program stepping through and able to return to where the next line of program was.

 

[hippy]

Within the I/O code, you aren't actually nesting GOSUB's, but entering the single routine, branching to a particular 'handler', then executing a RETURN after each handler. All will cause a continuation at the line after the initial GOSUB which started the ball rolling, and that is perfectly okay. You could have had each handler of the I/O routine finish by jumping to a single RETURN for the entire routine, but what you have is equally acceptable.

 

[ercotronic]

Hi again,
If the code above is ok, does this mean you can enter a subroutine without having to use a gosub command, (as the instruction was then delrc) and will the picaxe still treat itas a gosub and return ok (with the return instruction at the end of delrc
P.S. I accidentally omitted the ':' from the delrc subroutine in the code above.
regards Eric

 

[hippy]

No, a subroutine can only be entered by a GOSUB.

Once in a subroutine though, flow can be passed around in a sequential (GOTO) manner ...

- GOSUB MySub
:
- MySub:
- SELECT CASE b0
- CASE 1 : pin1 = 0
- CASE 2 : pin2 = 0
- END SELECT
- RETURN

could in PICAXE terms be written ...

- MySub:
- IF b0 = 1 THEN MySub_B0is1
- IF b0 = 2 THEN MySUb_B0is2
- GOTO MySub_Exit
- MySub_B0is1:
- pin1=0
- GOTO MySub_Exit
- MySub_B0is2:
- pin2=0
- GOTO MySub_Exit
- MySub_Exit:
- RETURN

That can be optimised by removing the GOTO MySub_EXit's as you effectively did in your own code to give ...

- MySub:
- IF b0 = 1 THEN MySub_B0is1
- IF b0 = 2 THEN MySUb_B0is2
- RETURN
-
- MySub_B0is1:
- pin1=0
- RETURN
-
- MySub_B0is2:
- pin2=0
- RETURN

There is still only one subroutine, called by the GOSUB, but it has multiple RETURN's rather than just a single RETURN point.

 

[ercotronic]

Hi,
many thanks Hippy I think the penny's dropped now. I'd tested the code and it seemed to work fine but I didn't Know if this was just luck and it may have caught me out at a later date. From your descriptoin of what is happening I see now why it works, I didn't know if you could have more than one return and the code still work reliably
I suppose this method may help Sollytear with
his program also.
many thanks