S912XEG128J2MAA Datasheet, PDF (381/1324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 10 XGATE (S12XGATEV3)
Writing a "1" to XGDBG and XGDBGM in the same write access causes the XGATE to enter
debug mode upon completion of the current instruction.
NOTE
After writing to the XGDBG bit the XGATE will not immediately enter
debug mode. Depending on the instruction that is executed at this time there
may be a delay of several clock cycles. The XGDBG will read "0" until
debug mode is entered.
2. Software breakpoints
XGATE programs which are stored in the internal RAM allow the use of software breakpoints. A
software breakpoint is set by replacing an instruction of the program code with the "BRK"
instruction.
As soon as the program execution reaches the "BRK" instruction, the XGATE enters debug mode.
Additionally a software breakpoint request is sent to the S12X_DBG module (see section 4.9 of
the S12X_DBG Section).
Upon entering debug mode, the program counter will point to the "BRK" instruction. The other
RISC core registers will hold the result of the previous instruction.
To resume program execution, the "BRK" instruction must be replaced by the original instruction
before leaving debug mode.
3. Tagged Breakpoints
The S12X_DBG module is able to place tags on fetched opcodes. The XGATE is able to enter
debug mode right before a tagged opcode is executed (see section 4.9 of the S12X_DBG Section).
Upon entering debug mode, the program counter will point to the tagged instruction. The other
RISC core registers will hold the result of the previous instruction.
4. Forced Breakpoints
Forced breakpoints are triggered by the S12X_DBG module (see section 4.9 of the S12X_DBG
Section). When a forced breakpoint occurs, the XGATE will enter debug mode upon completion
of the current instruction.
10.6.2 Leaving Debug Mode
Debug mode can only be left by setting the XGDBG bit to "0". If a thread is active (XGCHID has not been
cleared in debug mode), program execution will resume at the value of XGPC.
10.7 Security
In order to protect XGATE application code on secured S12X devices, a few restrictions in the debug
features have been made. These are:
• Registers XGCCR, XGPC, and XGR1–XGR7 will read zero on a secured device
• Registers XGCCR, XGPC, and XGR1–XGR7 can not be written on a secured device
• Single stepping is not possible on a secured device
MC9S12XE-Family Reference Manual Rev. 1.25
Freescale Semiconductor
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