
Debug Support
MOTOROLA
MCF5206 USERS MANUAL Rev 1.0
14-5
1. The occurrence of the catastrophic fault-on-fault condition automatically halts the
processor. The halt status is posted on the PST port ($F).
2. The occurrence of a hardware breakpoint (reference subsection Section 14.3 Real-
Time Debug Support) can be configured to generate a pending halt condition in a
manner similar to the assertion of the BKPT signal. In some cases, the occurrence of
this type of breakpoint halts the processor in an imprecise manner. Once the hardware
breakpoint is asserted, the processor halts at the next sample point. See Section
14.3.2 Theory of Operation for more detail.
3. The execution of the HALT (also known as BGND on the 683xx devices) instruction
immediately suspends execution and posts the halt status ($F) on the PST outputs.
By default, this is a supervisor instruction and attempted execution while in user mode
generates a privilege-violation exception. A User Halt Enable (UHE) control bit is
provided in the Configuration/Status Register (CSR) to allow execution of HALT in
user mode.
4. The assertion of the BKPT input pin is treated as an pseudo-interrupt, i.e., the halt
condition is made pending until the processor core samples for halts/interrupts. The
processor samples for these conditions once during the execution of each instruction.
If there is a pending halt condition at the sample time, the processor suspends
execution and enters the halted state. The halt status ($F) is reflected in the PST
outputs.
The halt source is indicated in CSR[27:24]; for simultaneous halt conditions, the highest
priority source is indicated.
There are two special cases to be considered that involve the assertion of the BKPT pin.
After RSTI is negated, the processor waits for 16 clock cycles before beginning reset
exception processing. If the BKPT input pin is asserted within the first eight cycles after RSTI
is negated, the processor enters the halt state, signaling that status on the PST outputs ($F).
While in this state, all resources accessible via the Debug module can be referenced. Once
the system initialization is complete, the processor response to a BDM GO command
depends on the set of BDM commands performed while breakpointed. Specifically, if the
processors PC register was loaded, the GO command causes the processor to exit the halt
state and pass control to the instruction address contained in the PC. In this case, the
normal reset exception processing is bypassed. Conversely, if the PC register was not
loaded, the GO BDM command causes the processor to exit the halt state and continue with
reset exception processing.
ColdFire 52xx processors also handle a special case with the assertion of BKPT while the
processor is stopped by execution of the STOP instruction. For this case when the BKPT is
asserted, the processor exits the stopped mode and enters the halted state. Once halted,
the standard BDM commands may be exercised. When the processor is restarted, it
continues with the execution of the next sequential instruction, i.e., the instruction following
the STOP opcode.
The debug module Configuration/Status Register (CSR) maintains status defining the
condition that caused the CPU to halt.
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Freescale Semiconductor, Inc.
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