S912XEG128J2MAA Datasheet, PDF (345/1324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 8 S12X Debug (S12XDBGV3) Module
executes the BDM firmware code. It checks the ENABLE and returns if ENABLE is not set. If not serviced
by the monitor then the breakpoint is re-asserted when the BDM returns to normal CPU12X flow.
If the comparator register contents coincide with the SWI/BDM vector address then an SWI in user code
and DBG breakpoint could occur simultaneously. The CPU12X ensures that BDM requests have a higher
priority than SWI requests. Returning from the BDM/SWI service routine care must be taken to avoid re
triggering a breakpoint.
NOTE
When program control returns from a tagged breakpoint using an RTI or
BDM GO command without program counter modification it will return to
the instruction whose tag generated the breakpoint. To avoid re triggering a
breakpoint at the same location reconfigure the S12XDBG module in the
SWI routine, if configured for an SWI breakpoint, or over the BDM
interface by executing a TRACE command before the GO to increment the
program flow past the tagged instruction.
An XGATE software breakpoint is forced immediately, the tracing session
terminated and the XGATE module execution stops. The user can thus
determine if an XGATE breakpoint has occurred by reading out the XGATE
program counter over the BDM interface.
MC9S12XE-Family Reference Manual Rev. 1.25
Freescale Semiconductor
345