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Realm Management Extension, (RME)
RME support is an APB5 feature for the Arm Realm Management Extension System Architecture. RME adds Root and Realm physical address spaces into the Arm architecture. These address spaces can be used in permission checks of APB transactions.
PNSE signal
PNSE (Physical Non-Secure Extension) is the APB5 signal added to support RME.
| Signal | Width | Source | Description |
|---|---|---|---|
| PNSE | 1 | Requester | Extension to protection type. PNSE must be valid when PSEL is asserted. |
If PNSE is present on an interface, PPROT must also be present.
The combination of PNSE and PPROT[1] identifies the physical address space:
| PNSE | PPROT[1] | Physical address space |
|---|---|---|
| 0 | 0 | Secure |
| 0 | 1 | Non-secure |
| 1 | 0 | Root |
| 1 | 1 | Realm |
RME Support configuration
RME support is controlled by the RME_Support interface property.
| RME_Support value | Meaning |
|---|---|
| True | RME is supported. PNSE is present on the interface. This can only be used on an APB5 interface. |
| False | RME is not supported. PNSE is not present on the interface. |
| Not declared | Treated as False. |
PNSE is parity protected using PCTRLCHK.
RME Support compatibility
Compatibility between Requester and Completer interfaces depends on the RME_Support property on each side.
| Requester RME_Support | Completer RME_Support | Compatibility |
|---|---|---|
| False | False | Compatible |
| False | True | Compatible. Tie the PNSE input LOW. |
| True | False | Not compatible |
| True | True | Compatible |
APB Protocol