SX/B Subroutine Parameters

Brian Riley

I wrote some code for my SX48 Robot that looks like

GoForward  SUB 1
GoBack       SUB 1
StopBot      SUB 1


GoForward:
   s1Pos = 75
   s2Pos = 200
   IF __PARAMCNT = 1 THEN
       temp1 = __PARAM1
       pause temp1*250
   ENDIF
   RETURN

the remaining subs are essentially the same just the numbers to the servos are different the idea being if the routine is called with no paremeter it just starts the Bot moving Forward or backward or stops it while it awaits some senoer input to cause it to decide to do something different. If it gets called with a parameter that number is multiplied by 250 (1/4 second) and the pause command lets it move in that direction for that amount of time before being free to read sensors.

If I declare the SUB with 1 parameter I get an "invalid number of parameters errors" for the parameterless call if I declare it

GoForward  SUB 0 1

I get the same error against a call to the sub with parameters.

The simple workaround is to make semi-duplicate SUBS, but that is wasteful. The documentation is fairly clear on 1 or 2 paremeters, but I just cannot figure out how to appease the compiler for selectin between 0 and 1 parameter.

Is this a bug, if not how do I make it work?


TNX

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cheers ... brian riley, n1bq, underhill center, vermont

Jon Williams

When defining subs that could have multiple parameters, you need to do it like this (note the comma):

GO_FORWARD····· SUB··· 0, 1

Then check and pick-up any parameters before doing anything else in your sub -- otherwise the internal variables that carry parameters (__PARAMx) could get clobbered.

GO_FORWARD:
· IF __PARAMCNT = 1 THEN
··· temp1 = __PARAM1
· ELSE
··· temp1 = 1
· ENDIF
· servo1 = 75
· servo2 = 200
· IF temp1 > 0 THEN
··· PAUSE temp1 * 250
··ENDIF
· RETURN

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Jon Williams
Applications Engineer, Parallax

Post Edited (Jon Williams (Parallax)) : 9/22/2005 9:17:23 PM GMT

Jon Williams

Since delays are often needed and PAUSE and PAUSEUS take up a bit of code every time thery're used, I tend to have these subroutines in most of my SX/B programs...

The declarations:

WAIT_US··SUB·1, 2·········· ··' delay in microseconds
WAIT_MS··SUB·1, 2·············' delay in milliseconds

And the code:

' Use: WAIT_US microseconds {, multiplier}
' -- multiplier is optional

WAIT_US:
· temp1 = __PARAM1·········· ·' get microseconds
· IF __PARAMCNT = 1 THEN···· ·' if no multiplier
··· temp2 = 1··········· ··· ·'·· set to 1
· ELSE························' else
··· temp2 = __PARAM2······· ··'·· get multiplier
· ENDIF
· IF temp1 > 0 THEN···········' no delay if either 0
··· IF temp2 > 0 THEN
····· PAUSEUS temp1 * temp2···' do the delay
··· ENDIF
· ENDIF
· RETURN

' Use: WAIT_MS milliseconds {, multiplier}
' -- multiplier is optional

WAIT_MS:
· temp1 = __PARAM1········· ·' get milliseconds
· IF __PARAMCNT = 1 THEN··· ·' if no multiplier
··· temp2 = 1············ · ·'·· set to 1
· ELSE····················· ·' else
··· temp2 = __PARAM2······· ·'·· get multiplier
· ENDIF
· IF temp1 > 0 THEN········ ·' no delay if either 0
··· IF temp2 > 0 THEN
····· PAUSE temp1 * temp2··· ' do the delay
··· ENDIF
· ENDIF
· RETURN

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Jon Williams
Applications Engineer, Parallax

Brian Riley

Jon Williams (Parallax) said...
When defining subs that could have multiple parameters, you need to do it like this (note the comma):

GO_FORWARD SUB 0, 1

Then check and pick-up any parameters before doing anything else in your sub -- otherwise the internal variables that carry parameters (__PARAMx) could get clobbered.

GO_FORWARD:
IF __PARAMCNT = 1 THEN
temp1 = __PARAM1
ELSE
temp1 = 1
ENDIF
servo1 = 75
servo2 = 200
IF temp1 > 0 THEN
PAUSE temp1 * 250
ENDIF
RETURN

Thanks Jon. This helps a lot. I am on the road in NJ with just my PowerBook. But to my recollection the example code shows some subroutines fpr DELAY and DELAYUS that shows

DELAY SUB 1 2

without the comma. (or I misread it! ... mea culpa!)

Also thanks for the routines you posted I am going to add them to the serial string handling routines as part of a 'standard include' file I am building.

When I get back early next week (my #1 son is gettin married tomorrow) look for some SX48 Robot code coming forth with IR sensing collison avoidance.

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cheers ... brian riley, n1bq, underhill center, vermont