Memory Management Features - 2022.1 English

MicroBlaze Processor Embedded Design User Guide (UG1579)
Document ID
UG1579
Release Date
2022-06-01
Version
2022.1 English
  • Data Shadow Translation Look-Aside Buffer Size: Defines the size of the instruction shadow translation look-aside buffer (TLB). This TLB caches data address translation information, to improve performance of the translation. The selection is a trade-off between smaller size and better performance: the default value is 4.
  • Instruction Shadow Translation Look-Aside Buffer Size: Defines the size of the instruction shadow translation look-aside buffer (TLB). This TLB caches instruction address translation information to improve performance of the translation. The selection is a trade-off between smaller size and better performance: the default value is 2.
  • Enable Access to Memory Management Special Registers: Enables access to the memory management special register using the MFS and MTS instructions:
    • Minimal (0) only allows writing TLBLO, TLBHI, and TLBX.
    • Read (1) adds reading to TLBLO, TLBHI, TLBX, PID, and ZPR.
    • Write (2) allows writing all registers, and reading TLBX.
    • Full (3) adds reading of TLBLO, TLBHI, TLBX, PID, and ZPR.

    In many cases, it is not necessary for the software to have full read access. For example, this is the case for Linux memory management code. It is then safe to set access to Write, to save area. When using static memory protection, access can be set to Minimal, because the software then has no need to use TLBSX, PID, and ZPR.

  • Number of Memory Protection Zones: Specifies the number of memory protection zones to implement. In many cases memory management software does not use all available zones. For example, the Linux memory management code only uses two zones. In this case, it is safe to reduce the number of implemented zones, to save resources.
  • Privileged Instructions: Specifies which instructions to allow in User Mode.
    • Full Protection (0): Ensures full protection between processes.
    • Allow Stream Instructions (1): Makes it possible to use AXI4-Stream instructions in User Mode.
    • Allow Extended Address Instruction (2): Makes it possible to use extended load/store instructions when available.
    • Allow Both (3): Allows both types of instructions.
    CAUTION:
    It is strongly discouraged to change this setting from Full Protection, unless it is necessary for performance reasons.