ElmoMC SimplIQ Software Manual - Manual (Page 95)

SimplIQ Software Manual Program Development and Execution
MAN-SIMSW (Ver. 1.4)
6-33
6.7.12 Retrieving the Call Stack
There is no direct command for retrieving a call stack. The IDE manager executes all debug
analysis.
Example (more details provided in section 8.2 ):
Stack Pointer
Relative to
Base Pointer
Meaning
Remarks
BP-5 Saved previous BP BP is 0 for first called function
BP-4 Return address Program counter of next
program line after function call
BP-3 Index of current function in
Function Symbol table See section A.5.5 .
BP-2 Number of input arguments
BP-1 Number of actual output arguments Number of left-hand values
during function call
This information can assist in restoring a call stack as follows:
When the first function is called, its BP is zero. Every subsequent function during its call saves
the previous base pointer in the stack at BP-5, so that it can restore BP upon return from the
function. To get the entire call stack, the previous base pointer must be rolled back in the loop
until BP becomes zero. The process to restore the call stack is as follows:
ƒ DB##PS[N];
Get current status
ƒ Check current status: if it is not halted, return an error.
ƒ BP_last = BP; Get current BP from data returned by DB##PS
ƒ N1 = 0; Index of the bottom of the stack
ƒ N2 = SP; Index of the top of the stack
ƒ DB##GS=N1,N2; Get entire stack
ƒ do Start do-while loop until BP_last is not 0
ƒ funcIndex = BP_last - 3 ; Get called function index in Symbol table and insert
in call stack
ƒ if (BP_last == 0) break ; This is the first called function
ƒ BP_last = BP_last - 5 : Update
BP_last
ƒ while (1) End of do-while loop
6.7.13 Viewing Global Variables
Global variables may be accessed through the Interpreter; there is no need for a special
debug command.