THE MECHANISM
The MPU checks every access.
Select an access to follow it from the unprivileged context through the MPU check to the outcome. The region table is an example policy. Your configuration defines the real one.
BOUNDARIES
Make access deliberate.
01
Protect kernel state
Keep privileged kernel data outside the regions unprivileged application code can write.
Start with the regions each part of the application needs. Express those boundaries in the target's memory protection configuration.
02
Define application regions
Plan access to code, data and stacks. Match the separation you need to the regions the hardware can enforce.
03
Share through explicit permissions
Grant access to selected buffers and device registers where needed.
FAULT RESPONSE
Detect the violation.
Define the response.
01 / ACCESS
A CPU access violates policy
The address, access type and privilege level are checked against the active region configuration.
02 / FAULT
The processor raises a fault
Exception handling follows the target architecture and fault configuration.
03 / RESPONSE
Software handles the event
Diagnostic capture and any stop, restart or reset behavior belong to the implemented fault policy.
Fault detection and system recovery are separate design decisions.
TARGET FIT
Fit the boundaries to your hardware.
The CPU, memory layout and QRT port determine the protection configuration available to your application.
Hardware and port
Confirm the exact device, protection hardware and supported QRT configuration.
Privilege and peripherals
Identify privileged code, device register access and the controls for DMA and other bus masters.
Region budget and layout
Account for region count, alignment and granularity when placing code, data, stacks and shared buffers.
Behavior under test
Exercise permitted and denied accesses. Record the fault path and measure any configuration or context switch overhead.
DESIGN QUESTIONS
Know where the boundary is.
Does memory protection catch every invalid access?
It checks accesses against the configured region permissions. A bad pointer that still points inside an allowed writable region can corrupt data there. Region protection does not provide object-level bounds checking.
Does a CPU MPU also control DMA?
DMA and other bus masters have their own access paths. Check the device's system-level protection and peripheral configuration; CPU MPU permissions alone do not establish their access policy.
Can execution continue after a protection fault?
That depends on the implemented handler, application state and recovery policy. The presence of memory protection alone does not establish that execution can continue or that an individual task can be restarted.
Get Started
Talk to the team
Reach out to the team for licensing, technical questions, or evaluation.
contact@preemptsystems.com
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