MC9S12XD256MAL Datasheet, PDF (207/1348 Pages) Freescale Semiconductor, Inc – Freescale’s Scalable Controller Area Network

Chapter 6 XGATE (S12XGATEV2)
• Single Stepping
Writing a "1" to the XGSS bit will call the RISC core to execute a single instruction. All RISC core
registers will be updated accordingly.
• Write accesses to the XGCHID register
Three operations can be performed by writing to the XGCHID register:
– Change of channel ID
If a non-zero value is written to the XGCHID while a thread is active (XGCHID ≠ $00), then
the current channel ID will be changed without any influence on the program counter or the
other RISC core registers.
– Start of a thread
If a non-zero value is written to the XGCHID while the XGATE is idle (XGCHID = $00),
then the thread that is associated with the new channel ID will be executed upon leaving
debug mode.
– Termination of a thread
If zero is written to the XGCHID while a thread is active (XGCHID ≠ $00), then the current
thread will be terminated and the XGATE will become idle.
6.6.2 Entering Debug Mode
Debug mode can be entered in four ways:
1. Setting XGDBG to "1"
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.
MC9S12XDP512 Data Sheet, Rev. 2.21
Freescale Semiconductor
207