The implementation of Physical Memory Protection on Boom

[Chen Chen]

Hi,

I would like to understand how the physical memory protection is implemented on Boom. 

I compiled SmallBoomV3 and SmallBoomV4 with the default setup and then tried to access PMP CSRs to change the configuration. According to RISC-V manual (Volumne II Privileged Architecture Version 20240411), (i) Implementations may implement zero, 16, or 64 PMP entries, and (ii) RV64 processors have eight even-numbered CSRs (pmpcfg0, ..., pmpcfg14). Then, I wrote a test to access eight CSRs. However, I can only access part of them (pmpcfg0,13,14). I run the same test on Spike, which works as stated in the manual (pmpcfg0,2) if only 16 entries are implemented. 

I also checked the parameters.scala of v3 and v4. The nPMPs is set up by 8. 

I have attached the source code, which is compiled in baremetal mode. Please let me know if I made any mistakes. 

Thank you very much!

Chen

Commit version: Chipyard 1.13.0

Output from BoomV3:

Initial PMP Configurations:
pmpcfg0:  0x03000301
pmpcfg1:  0x00000000
pmpcfg2:  0x00000000
pmpcfg3:  0x00000000
pmpcfg4:  0x00000000
pmpcfg5:  0x00000000
pmpcfg6:  0x00000000
pmpcfg7:  0x00000000
pmpcfg8:  0x00000000
pmpcfg9:  0x00000000
pmpcfg10:  0x80003390
pmpcfg11:  0x00000000
pmpcfg12:  0x80002668
pmpcfg13:  0x00000000
pmpcfg14:  0x00000000
pmpcfg15:  0x00000000
Updated PMP Configurations:
Updated pmpcfg0:  0x0000000f
Updated pmpcfg1:  0x00000000
Updated pmpcfg2:  0x00000000
Updated pmpcfg3:  0x00000000
Updated pmpcfg4:  0x00000000
Updated pmpcfg5:  0x00000000
Updated pmpcfg6:  0x00000000
Updated pmpcfg7:  0x00000000
Updated pmpcfg8:  0x00000000
Updated pmpcfg9:  0x00000000
Updated pmpcfg10:  0x80003390
Updated pmpcfg11:  0x00000000
Updated pmpcfg12:  0x80002bd0
Updated pmpcfg13:  0x0000000f
Updated pmpcfg14:  0x0000000f
Updated pmpcfg15:  0x00000000

Output from Spike:

Initial PMP Configurations:
pmpcfg0:  0x0000001f
pmpcfg1:  0x00000000
pmpcfg2:  0x00000000
pmpcfg3:  0x00000000
pmpcfg4:  0x00000000
pmpcfg5:  0x00000000
pmpcfg6:  0x00000000
pmpcfg7:  0x00000000
pmpcfg8:  0x00000000
pmpcfg9:  0x00000000
pmpcfg10:  0x00000000
pmpcfg11:  0x00000000
pmpcfg12:  0x80002668
pmpcfg13:  0x00000000
pmpcfg14:  0x00000000
pmpcfg15:  0x00000000
Updated PMP Configurations:
Updated pmpcfg0:  0x0000000f
Updated pmpcfg1:  0x00000000
Updated pmpcfg2:  0x0000000f
Updated pmpcfg3:  0x00000000
Updated pmpcfg4:  0x00000000
Updated pmpcfg5:  0x00000000
Updated pmpcfg6:  0x00000000
Updated pmpcfg7:  0x00000000
Updated pmpcfg8:  0x00000000
Updated pmpcfg9:  0x00000000
Updated pmpcfg10:  0x00000000
Updated pmpcfg11:  0x00000000
Updated pmpcfg12:  0x80002b94
Updated pmpcfg13:  0x00000000
Updated pmpcfg14:  0x00000000
Updated pmpcfg15:  0x00000000