
MOTOROLA
Chapter 23. Development Support
23-29
Development System Interface
When the processor is in debug mode the freeze indication is asserted thus allowing any
peripheral that is programmed to do so to stop. The fact that the CPU is in debug mode is
also broadcast to the external world using the value b11 on the VFLS pins.
NOTE
The freeze signal can be asserted by software when debug
mode is disabled.
The development port should read the value of the exception cause register (ECR) in order
to get the cause of the debug mode entry. Reading the exception cause register (ECR) clears
all its bits.
23.3.1.3 Check Stop State and Debug Mode
The CPU enters the check stop state if the machine check interrupt is disabled
(MSR[ME] = 0) and a machine check interrupt is detected. However, if a machine check
interrupt is detected when MSR[ME] = 0, debug mode is enabled and the check stop enable
bit in the debug enable register (DER) is set, the CPU enters debug mode rather then the
check stop state.
The different actions taken by the CPU when a machine check interrupt is detected are
shown in the following table.
23.3.1.4 Saving Machine State upon Entering Debug Mode
If entering debug mode was as a result of any load/store type exception, and therefore the
DAR (data address register) and DSISR (data storage interrupt status register) have some
significant value, these two registers must be saved before any other operation is
performed. Failing to save these registers may result in loss of their value in case of another
load/store type exception inside the development software.
Table 23-9. Check Stop State and Debug Mode
MSR[ME]
Debug
Mode
Enable
CHSTPE 1
1 Check stop enable bit in the debug enable register (DER)
MCIE 2
2 Machine check interrupt enable bit in the debug enable register (DER)
Action Performed by the CPU when
Detecting a Machine Check Interrupt
Exception Cause
Register (ECR)
Value
0
X
Enter the check stop state
0x2000_0000
1
0
X
Branch to the machine check interrupt
0x1000_0000
0
1
0
X
Enter the check stop state
0x2000_0000
0
1
X
Enter Debug Mode
0x2000_0000
1
X
0
Branch to the machine check interrupt
0x1000_0000
1
X
1
Enter Debug Mode
0x1000_0000