Software Stack
Hi anybody
Several days ago I found a program that was about 48 level Software Stack on a 14-bit Core PIC.
http://www.pbpgroup.com/modules/wfse...p?articleid=14
That's really great but I have some questions about it.
1- It includes an .inc file as below:
'************************************************* ***************
'* Name : swStack.inc *
'* Author : Darrel Taylor *
'* Date : 11/26/2003 *
'* Version : 1.0 *
'* Notes : Software Stack for PicBasic Pro *
'* : Allows up to 48 level Gosub Stack *
'* : on a PIC with an 8 level Hardware Stack *
'* : Tested with 16F877 on a LAB-X2 *
'************************************************* ***************
'* Many thanks to John Barrat for solving the *
'* Forwand Declaration problem with nested macros *
'************************************************* ***************
Stack Var Word[StackSize] ' This is the Stack
StackPTR Var Byte ' Pointer to Top of Stack
StackFull Var bit ' if=1, you cannot do another swGosub
StackEmpty var bit ' if=1, you cannot do a swReturn
SToverflow var bit ' swGosub called when Stack was Full
STunderflow var bit ' swReturn called when Stack was Empty
Address Var Word ' internal use only
StackEmpty = 1 ' Start with an Empty Stack
goto OverStack
'------------GetAddress Macro - Location insensitive -------------------------
ASM
GetAddress macro Label, Wout ; Returns the Address of a Label as a Word
CHK?RP Wout
movlw low Label
movwf Wout
movlw High Label
movwf Wout + 1
endm
ENDASM
'------------GOTO the address from a word variable.---------------------------
ASM
GotoAddress macro Win ; goto address specified by Win parameter
CHK?RP Win
movf Win + 1, W
movwf PCLATH ; Set PCH via PCLATH
movf Win, W
RST?RP
movwf PCL ; Writing to PCL will also load PCLath
endm ; into PCH
ENDASM
'------------Push Address onto the Stack--------------------------------------
Push:
if StackFull = 0 then ; If Stack isn't Full
Stack[StackPTR] = Address ; Add Address to the Stack
StackPTR = StackPTR + 1 ; Point to next Stack level
StackEmpty = 0 ; 0 - Since we just put something in it
else
SToverflow = 1 ; Stack was full, but you tried it again
endif
if StackPTR = StackSize then StackFull = 1 ; Update Full status
return
'------------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
'------------Gosub using Software Stack---------------------------------------
asm
swGosub macro Label
local ReturnPoint ; Local label
GetAddress ReturnPoint, _Address ; Get address of Return Point
L?CALL _Push ; Push Return Point on the Stack
GetAddress Label, _Address ; Get address of the Subroutine
GotoAddress _Address ; goto the Subroutine
ReturnPoint ; This is where swReturn will return to
endm
endasm
'------------Return using Software Stack---------------------------------------
Asm
swReturn macro
L?CALL _Pop ; Pop last Return Point from the Stack
GotoAddress _Address ; Goto the Return Point
endm
Endasm
OverStack:
()()()()()()()()()()()()()()()()()()()()()()()()() ()()()()()()()()()()()()()()()()()()()()()()()()
As you see there is a label without any thing. What happens when program jumps to this part especially after "goto OverStack"
There are some unknown instructions in asm parts for example:
CHK?RP
L?CALL
How can I interpret them?
2- The author has given an example of using this .inc file:
'************************************************* ***************
'* Name : Test_swStack.pbp *
'* Author : Darrel Taylor *
'* Date : 11/26/2003 *
'* Version : 1.0 *
'* Notes : Software Stack Demo (requires swStack.inc) *
'* : Tested with 16F877 on a LAB-X2 *
'* : View the output with HyperTerminal @ 9600 baud *
'************************************************* ***************
define LOADER_USED 1
define OSC 4
clear
' StackSize must be defined before include file
StackSize Con 20 ' Maximum StackSize is limited by the largest
' Word Array that you can fit in 1 bank
' Also, on an 18F type part the only limit is the
' Total amount of RAM (Big Stack)
include "swStack.inc" ' Include Software Stack routines
' SetUp Hardware USART
DEFINE HSER_TXSTA 24h ' Use this for Higher Baud Rates
DEFINE HSER_SPBRG 25 ' 9600 Baud at 4mhz
DEFINE HSER_CLROERR 1 ' Hser clear overflow automatically
CR Con 13 : LF Con 10 ' Carriage Return and Line Feed constants
hserout [27,"[2J"] ' Clear HyperTerminal screen
goto StartTest
'----- Simple swGosubs one after the other -----------------------------------
Sub1: ; Note how you can "nest" normal Gosubs within
Hserout ["Sub1 -"] ; a Software Gosub. Giving 4 additional levels.
gosub ShowStack ; Just "BE SURE" to match a GOSUB with a RETURN
@ swGosub _Sub2 ; and a swGosub with a swReturn
@ swReturn ;
Sub2:
Hserout ["Sub2 -"]
gosub ShowStack
@ swGosub _Sub3
@ swReturn
Sub3:
Hserout ["Sub3 -"]
gosub ShowStack
@ swReturn
StartTest:
Hserout ["--- Simple Test ---",cr,lf]
@ swGosub _Sub1 ; Software Gosub to Sub1, 2, 3
@ swGosub _Sub2 ; 2, 3
@ swGosub _Sub3 ; 3
'----- Recursive Test -------------------------------------------------------
TestLevel con StackSize
'TestLevel con StackSize + 1 ' uncomment to cause an OverFlow (not pretty)
Dir var bit
Hserout ["--- Recursive Test ---",cr,lf]
RecurseTest: ' swGosub's to itself until the Stack is Full
if StackFull = 1 then hserout ["Full -"] : gosub ShowStack
if Dir = 0 then
if StackPTR = TestLevel then
Dir = 1
else
hserout ["Enter-"] : gosub ShowStack
@ swGosub _RecurseTest ; The recursive GOSUB
hserout [" Exit-"] : gosub ShowStack
endif
EndIf
if Dir = 1 then
if StackEmpty = 1 then
Dir = 0
Hserout [cr,lf]
goto StartTest ' RecurseTest finished - Restart Simple test
else
@ swReturn ; Back out of Recursive Loop
endif
endif
Stop ' Should never make it here
'----- Display Stack Status --------------------------------------------------
ShowStack:
hserout ["StackPTR = ", dec StackPTR," Full=",dec StackFull," Empty=", _
dec StackEmpty," OFL=", dec SToverflow," UFL=",dec STunderflow,cr,lf]
pause 50
return
End
- Can anuone help me about knowing Hyperterminal?
- Can I display results on LCD instead of Hyperterminal? If yes HOW?
Thanks alot.
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