Software description

AN421

6/11

Doc ID 2476 Rev 2

3

Software description

3.1

Stack initialization

The following example initializes the system stack in groups D and C of the Register File.

In the stack management of the ST9, the stack pointer is automatically pre-decremented

before the data is stored on the stack. So the expression:

SSTACK = (BKE * 16) - 1

defines the first location of the system stack in group D and C within the Register File, while

the instruction:

ld SSPLR,#SSTACK + 1

initializes the system stack pointer in the system register. The instruction:

ldw RR#END_SSTACK,#0AA55h

initializes the first two bytes following the bottom of the system stack with the value used to

restart the Timer/Watchdog. Initialization

Figure 2.

System stack initialization

;***************************************************************

; STACK Declaration and end of stack initialisation

; in RAM space or Register File

;***************************************************************

; Initialisation in Register FIle

SSTACK := (BKE * 16) - 1

; Sys.stack add.group

LG-SSTACK := 32 ; Sys.stack length

END_SSTACK := (BKE * 16) - LG_SSTACK

; Last sys.stack byte

ld SSPLR,#SSTACK + 1

; Load sys.stack pointer

ldw RR#END_STACK - 2,#0AA55h

; Init end of stack.

; Initialisation in RAM space

SSTACK := 2000h

; top of sys.stack

END-STACK := 1000h

; Init end of stack

essp = rr0

sdm

ldw SSPR,#SSTACK

; Select data space

ld essp,#END_SSTACK

; Init End of sys.stack

ldw -2(essp),#0AA55h