12.3.2.2 PPU Control
The PPU_CTRL register provides an ENABLE bit that allows bypassing all PPU checking when set to 0. In this case, the rest of the
PPU registers have no effect, and no access faults will occur. This is the reset state of the SMU.
When the ENABLE bit of PPU_CTRL register is asserted, access protection is configured on a peripheral-by-peripheral basis using the
SMU_PPUPATDx register(s). Setting a bit in the SMU_PPUPATDx register to one configures the corresponding peripheral controlled by
that bit to privileged access only. The single bit mode control for each peripheral provides fast hardware context switching for peripheral
sharing, while still supporting fast software context switches for task-based CPU context switching.
Note:
The SMU itself is a peripheral which has protection afforded by the PPU. A proper security/privilege context configuration re-
quires setting of the SMU's access control bits properly at startup so that only a top-level task (e.g., a uVisor from ARM) can perform
security/privilege context switches.
When a peripheral has access protection configured and the peripheral is accessed with invalid privilege credentials, then an access
fault occurs. The corresponding interrupt flag in SMU_IF is asserted and the ID of the peripheral for which an unpriviliged access was
attempted is captured in the PERIPHID bit-field of the
register (SMU_PPUFS). This peripheral ID is held stable until
all PPU interrupt flags are cleared to ensure that the first unprivileged access that caused the fault is not overwritten due to subsequent
faults before being acknowledged by software.
Note:
In the case of simultaneously occurring faults (which may be possible in some systems), only one of the faults' peripheral IDs will
be captured. There is no inherent peripheral priority defined that would result in one peripheral being recognized before another.
12.4 Register Map
The offset register address is relative to the registers base address.
Offset
Name
Type
Description
R
W1
(R)W1
RW
RW
RW
PPU Privilege Access Type Descriptor 0
RW
PPU Privilege Access Type Descriptor 1
R
Reference Manual
SMU - Security Management Unit
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