Module regions

Definitions about the memory / page and conventions. Include some helper functions to do the conversion.

The virtual address (32-bit) structure is as follows:

| 31                 22 | 21             12 | 11           0 |
| Page Directory Offset | Page Table Offset | In-Page Offset |

The page table entry (PTE, 32-bit) structure is as follows:

| 31                 12 | 11               6 | 5                0 |
| Physical Frame number | Flags for hardware | Flags for software |

Constants

• KERNBASE
  Kernel memory starts from here
• KSEG1
  KSEG1 Segment
• KSTACKTOP
  Kernel stack end at here (the end in the linking script).
• NASID
  The maximum count of all the asid
• PAGE_SIZE
  The physical page size (in bytes).
• PDMAP
  Bytes mapped by a page directory entry.
• PDSHIFT
  Shifted the Page Table Offset and In-Page Offset out to get the Page Directory Offset
• PGSHIFT
  Shifted the In-Page Offset out to get the Page Table Offset
• PTE_C_CACHEABLE
  Cache Coherency Attributes bit. If set, this entry is cache-able.
• PTE_D
  Dirty bit, but really a write-enable bit. 1 to allow writes, 0 and any store using this translation will cause a tlb mod exception (TLB Mod).
• PTE_G
  Global bit. When this bit in a TLB entry is set, that TLB entry will match solely on the VPN field, regardless of whether the TLB entry’s ASID field matches the value in EntryHi.
• PTE_HARDFLAG_SHIFT 🔒
  Page table / directory entry flag shift
• PTE_V
  Valid bit. If 0 any address matching this entry will cause a tlb miss exception (TLBL/TLBS).
• PTMAP 🔒
  Bytes mapped by a page table entry (Actually is the PAGE_SIZE).
• UCOW
  Reserved for COW (start address).
• UENVS
  The kernel array ENVS will be mapped here.
• ULIM
  The high-limits of user’s memory
• UPAGES
  The kernel array PAGES will be mapped here.
• USTACKTOP
  Normal user stack top.
• UTEMP
  Reserved for temporary usage (start address).
• UTEXT
  User test segment start.
• UTOP
  The uer’s space higher boundary.
• UVPT
  User’s page tables are stored here (for a PDMAP size).
• UXSTACKTOP
  The exception stack top for the user. See also: UTOP.