Some peripherals have split security access, meaning they can handle both secure and non-secure access. A subset of the peripheral's functions can be secure, while another subset is non-secure. The security is configured using SPU registers.
The peripheral instantiation table in Instantiation details the peripherals with split access.
Split security access is handled either on the register level or on the bit level, as explained in the following sections.
Register level split security access
For this group of peripherals, security is enforced at the register level. Split security settings apply for the entire register. Illegal access to the register will trigger a security fault. For example, if a register is configured as secure and the register is accessed from non-secure code, a security fault with a bus fault will be generated. A security fault due to an illegal access triggers the SPU event PERIPHACCERR.
Bit level split security access
For this group of peripherals, security is enforced at the register bit level. Split security settings are applied to individual bits of the register. The register supports access from both secure and non-secure code.
- Writing a secure bit from non-secure code will have no effect
- Reading a register from non-secure code will return 0 for all bits that are secure
- Non-secure write access to the register will not change bit i
- Non-secure read access to the register will read 0 for the bit at position i
Interrupts
Some peripherals have split security interrupts. This means the interrupt can be configured with a security attribute.
An interrupt may be generated during secure or non-secure execution, and the interrupt handler is executed based on the interrupt's security attribute.
Interrupts implement split security at the register level. For instance, if interrupt 0 is configured as secure and there is a non-secure read/write access to registers INTEN0, INTENSET0, INTENCLR0, or INTPEND0, a security fault with a bus fault will be generated.
Interrupts are generated when enabled events are triggered. When an event for a split security interrupt is triggered, the following applies.
- If an interrupt is configured as secure, an event associated to either a secure or non-secure feature can trigger the interrupt.
- If an interrupt is configured as non-secure, only events associated with non-secure features can trigger the interrupt.
An attempt to enable an interrupt for an event that does not match the ownership and security settings of the interrupt will be ignored and a security fault is not generated.