Physical Memory Protection (PMP)

The CV32E40S includes the Physical Memory Protection (PMP) unit. The PMP is both statically and dynamically configurable. The static configuration is performed through the top level parameters PMP_NUM_REGIONS and PMP_GRANULARITY. The dynamic configuration is performed through the CSRs described in Control and Status Registers.

The PMP_GRANULARITY parameter is used to configure the minimum granularity of PMP address matching. The minimum granularity is 2 ^{PMP_GRANULARITY+2} bytes, so at least 4 bytes.

The PMP_NUM_REGIONS parameter is used to configure the number of PMP regions, starting from the lowest numbered region. All PMP CSRs are always implemented, but CSRs (or bitfields of CSRs) related to PMP entries with number PMP_NUM_REGIONS and above are hardwired to zero.

The reset value of the PMP CSR registers can be set through the top level parameters PMP_PMPNCFG_RV[], PMP_PMPADDR_RV[] and PMP_MSECCFG_RV. PMP_PMPNCFG_RV[] is an array of PMP_NUM_REGIONS entries of the type pmpncfg_t. Entry N determines the reset value of the pmpNcfg bitfield in the pmpcfg CSRs. PMP_PMPADDR_RV[] is an array of PMP_NUM_REGIONS entries of logic [31:0]. Entry N determines the reset value of the pmpaddrN CSR. PMP_MSECCFG_RV is of the type mseccfg_t and determines the reset value of the mseccfg CSR.

The PMP is compliant to [RISC-V-PRIV] and [RISC-V-SMEPMP].

Debug mode

Accesses to the Debug Module region, as defined by the DM_REGION_START and DM_REGION_END parameters, while in debug mode are treated specially.

In order for debug to always be possible, the PMP will not disallow fetches, loads, or stores in the Debug Module region when the hart is in debug mode, regardless of how the PMP is configured.