Hi there,
Does CLEAR command clear the return address of a subroutine on the stack ?
Thanks.
===============================
Hi there,
Does CLEAR command clear the return address of a subroutine on the stack ?
Thanks.
===============================
"If the Earth were a single state, Istanbul would be its capital." Napoleon Bonaparte
No - the stack space is not part of the data space. Just your defined variables and PBP (internal) defined variables are cleared.
Paul Borgmeier
Salt Lake City, UT
USA
__________________
Thanks Paul.
Other then hard reset, how do I clear return adresses?
"If the Earth were a single state, Istanbul would be its capital." Napoleon Bonaparte
I haven't tried it myself...but...
Looking thru the datasheet for the 18F4620, I see:
TOSU, TOSH, TOSL (top of stack, upper, high, low) and the STKPTR register. Looks like the contents of STKPTR are Read/Write. So, in theory, you should be able to decrement the value in the low 5 bits of STKPTR and thereby 'POP' the last 'PUSH' off the stack.
SAYZER,
On 16 bit devices (e.g., 18F), you can reset the STKPTR = 0 to "clear" all the addresses on the stack. The values really are not cleared - but the stack pointer points to the first location (0) and does not know about the "old" values. You could actually clear them if you wanted as Ski noted but the pointer tells the PIC where to place and get stack data.
On 14 or lesser bit devices (e.g., 16F or lesser), you cannot clear the Stack (it is a circular buffer and does not reside in program or data space).
NOTE: you must be very careful messing with the Stack because behind the scenes, PBP uses it!
Paul Borgmeier
Salt Lake City, UT
USA
__________________
Hi, Sayzer
I didn't look at it very closely ...
but I feel you can find your solution Here :
http://www.pbpgroup.com/modules/wfse...p?articleid=14
and once more ...
Thanks to Whom ????
D.A.R.R.E.L. !!!! ..........
Alain
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Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
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IF there is the word "Problem" in your question ...
certainly the answer is " RTFM " or " RTFDataSheet " !!!
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Darrel's clever method for the 16F type PICs creates a software stack - the real "stack" is not in program or data space and cannot be accessed (unless there is a back door that nobody knows about as Ski suggested)
I guess that SAYZER could create a software stack (as Alain is suggesting) and then manipulate it as needed? SAYZER, what are you trying to do and with what family of PIC?
Paul Borgmeier
Salt Lake City, UT
USA
__________________
Hi, Paul
There's also something Doable ( depends on use ...) :
A GOSUB loads an address you can choose in the stack ...
if ending the SUB with a GOTO instead of a RETURN ... This address will stay as the new "return", "retfie" ... address.
That's used with the "RESUME Label" of PbP ...
I do not think "clearing" the stack would be really useful ... as a stack containing zeros will cause the device to reset ONLY its program on the first "return or so" met ...
Alain
Last edited by Acetronics2; - 9th February 2008 at 17:12.
************************************************** ***********************
Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
************************************************** ***********************
IF there is the word "Problem" in your question ...
certainly the answer is " RTFM " or " RTFDataSheet " !!!
*****************************************
As Alain mentioned, there are potential side effects If I start playing directly with the registers.
Instead now, I am using flags being set to zero before going to a subroutine, and set the flags if something inside the subroutine is used.
Then at the end of the subroutine(s), I am using a kind of select case with "GOTO".
This way, I don't have any "return" address to care for.
This is a little code eating though; but a lot safer.
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"If the Earth were a single state, Istanbul would be its capital." Napoleon Bonaparte
How about something like this:
Set your branch return location parameter, jump to the generic subroutine, branch back to wherever it came from. No calls, no gosubs, and so on...Code:main: code....code...code... addrreturn = 1 goto subroutine return1: addrreturn = 2 goto subroutine return2: addrreturn = 0 goto main subroutine: code....code....code branch addrreturn , [ return1 , return2, return3.................]
In the code, I jump from locations to locations really very fequently.
I am having a lot of return addresses.
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"If the Earth were a single state, Istanbul would be its capital." Napoleon Bonaparte
Ok, here is a simple example good enough to explain the issue.
Code:<font color="#000000">Begin: OK = <font color="#FF0000"><b>0 </b></font>MainMenu: <font color="#000080"><i>'...stuff is going on here... </i><b>IF </b></font>OK = <font color="#FF0000"><b>1 </b></font><font color="#000080"><b>THEN GOSUB </b></font>PrintMemory <font color="#000080"><b>GOTO </b></font>MainMenu PrintMemory: <font color="#000080"><b>IF </b></font>Memory = <font color="#FF0000"><b>0 </b></font><font color="#000080"><b>THEN </b></font>Begin <font color="#000080"><b>RETURN </b> <i>' IF this IF statement is true, then I get a useless Return address on Stack, and I get a lot of them. </i></font>
"If the Earth were a single state, Istanbul would be its capital." Napoleon Bonaparte
If you're careful, and I mean very, very careful, you could turn off the Stack Overflow/Underflow reset bits in the CONFIG and just not worry about the RETURN addresses...let them overflow as they will.
But again, you'd have to be very careful, especially if you nest any GOSUB's at all...so that might not work out at all.
Maybe take DT's Software Gosub example shown earlier and add your own subroutine to POP the last GOSUB address off the Software Stack.
Actually, I just looked at the code for the first time...
In the swStack.inc file, you could use this section:
You have access to the Pop subroutine.Code:'------------Pop Address from the Stack--------------------------------------- Pop: if StackPTR = 0 then StackEmpty = 1 ; Update Empty status if StackEmpty = 0 then ; If Stack isn't Empty Address = Stack[StackPTR-1] ; Get last Address from the Stack StackPTR = StackPTR - 1 ; Point to Prior Stack level StackFull = 0 ; 0 - Since we just removed 1 else STunderflow = 1 ; Stack was Empty on swReturn endif if StackPTR = 0 then StackEmpty = 1 ; Update Empty status return
But I'm guessing here...since I haven't used to swGosub/swReturn routines at all.........
You 'include' DT's software stack routines, your code above becomes:
Again, I'm guessing...Code:Begin: OK = 0 MainMenu: '...stuff is going on here... IF OK = 1 THEN @ swGOSUB PrintMemory ENDIF GOTO MainMenu PrintMemory: IF Memory = 0 THEN Gosub Pop 'regular Gosub here, generic, can be used system wide Goto BEGIN 'no more return address from the Gosub above ENDIF swRETURN
Last edited by skimask; - 19th February 2008 at 16:33.
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