Execution Control Modes - Texas Instruments TMS320C28x Reference Manual

7.4 Execution Control Modes

7.4.1 Stop Mode
The C28x supports two debug execution control modes:
Stop mode
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Real-time mode
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Stop mode provides complete control of program execution, allowing for the
disabling of all interrupts. Real-time mode allows time-critical interrupt service
routines to be performed while execution of other code is halted. Both execu-
tion modes can suspend program execution at break events, such as occur-
rences of software breakpoint instructions or specified program-space or
data-space accesses.
Stop mode causes break events, such as software breakpoints and analysis
watchpoints, to suspend program execution at the next interrupt boundary
(which is usually identical to the next instruction boundary). When execution
is suspended, all interrupts (including NMI and RS) are ignored until the CPU
receives a directive to run code again. In stop mode, the CPU can operate in
the following execution states:
Debug-halt state. This state is entered through a break event, such as
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the decoding of a software breakpoint instruction or the occurrence of an
analysis breakpoint/watchpoint. This state can also be entered by a re-
quest from the host processor. In the stop mode debug-halt state, the CPU
is halted. You can place the device into one of the other two states by giv-
ing the appropriate command to the debugger.
The CPU cannot service any interrupts, including NMI and RS (reset).
When multiple instances of the same interrupt occurs without the first
instance being serviced, the later instances are lost.
Single-instruction state. This state is entered when you tell the debug-
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ger to execute a single instruction by using a RUN 1 command or a
STEP 1 command. The CPU executes the single instruction pointed to by
the PC and then returns to the debug-halt state (it executes from one inter-
rupt boundary to the next). The CPU is only in the single-instruction state
until that single instruction is done.
If an interrupt occurs in this state, the command used to enter this state deter-
mines whether that interrupt can be serviced. If a RUN 1 command was
used, the CPU can service the interrupt. If a STEP 1 command was used, the
CPU cannot, even if the interrupt is NMI or RS.
Run state. This state is entered when you use a run command from the
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debugger interface. The CPU executes instructions until a debugger com-
mand or a debug event returns the CPU to the debug-halt state.
Execution Control Modes
Emulation Features 7-7