Chapter 8 S12X Debug (S12XDBGV3) Module
MC9S12XE-Family Reference Manual Rev. 1.21
Freescale Semiconductor
333
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Destination address of RTI, RTS, and RTC instructions.
Vector address of interrupts, except for SWI and BDM vectors
LBRA, BRA, BSR, BGND as well as non-indexed JMP, JSR, and CALL instructions are not classied as
change of ow and are not stored in the trace buffer.
COF addresses are dened as follows for the XGATE:
Source address of taken conditional branches
Destination address of indexed JAL instructions.
First XGATE code address in a thread
Change-of-ow addresses stored include the full 23-bit address bus of CPU12X, the 16-bit address bus for
the XGATE module and an information byte, which contains a source/destination bit to indicate whether
the stored address was a source address or destination address.
NOTE
When an CPU12X COF instruction with destination address is executed, the
destination address is stored to the trace buffer on instruction completion,
indicating the COF has taken place. If an interrupt occurs simultaneously
then the next instruction carried out is actually from the interrupt service
routine. The instruction at the destination address of the original program
ow gets exectuted after the interrupt service routine.
In the following example an IRQ interrupt occurs during execution of the
indexed JMP at address MARK1. The BRN at the destination (SUB_1) is
not executed until after the IRQ service routine but the destination address
is entered into the trace buffer to indicate that the indexed JMP COF has
taken place.
LDX
#SUB_1
MARK1
JMP
0,X
; IRQ interrupt occurs during execution of this
MARK2
NOP
;
SUB_1
BRN
*
; JMP Destination address TRACE BUFFER ENTRY 1
; RTI Destination address TRACE BUFFER ENTRY 3
NOP
;
ADDR1
DBNE
A,PART5
; Source address TRACE BUFFER ENTRY 4
IRQ_ISR
LDAB
#$F0
; IRQ Vector $FFF2 = TRACE BUFFER ENTRY 2
STAB
VAR_C1
RTI
;
The execution ow taking into account the IRQ is as follows
LDX
#SUB_1
MARK1
JMP
0,X
;
IRQ_ISR
LDAB
#$F0
;
STAB
VAR_C1
RTI
;
SUB_1
BRN
*
NOP
;
ADDR1
DBNE
A,PART5
;