289
Figure 27-3 shows an overview of this level of operation.
Figure 27-3. System/User Mode Setup for Operating System
27.3.4 Enabling the System/User Mode
The following steps describe how to enable the System/User Mode.
1. If a peripheral needs to be accessed while in User Mode, write to the appropriate user
enable register to allow that access.
2. Write a 1 to bit 0 of EDMR to enable System/User Mode.
3. Execute the SETUSR instruction to enter User Mode.
After the User Mode is entered, the limitations described earlier are in effect — writes to
protected registers will be ignored, Priority 3 is not available, and executing an IDET will
cause a System Mode Violation interrupt. Other features such as write protection may be
effect for user mode as well.
Return from interrupts
Interrupts,
SYSCALL, RST
System Mode
User Mode
Application
code
User-defined
interrupts
Interrupt
handlers
Flash file
system
SYSCALL
handler
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