Virtual to Physical Address Translation

The vmem.c​ and vmem.h​ files define the data structures and functions used by the boot-loader and the kernel to implement the paged virtual memory.

The page table initialisation is statically done by the boot-loader. There is one page table for each vspace defined in the mapping. When the architecture is clusterised (X_WIDTH > 1 or Y_WIDTH > 1), for each vspace, the page table is replicated in each cluster.

The virtual address format is 32 bits: structured in 3 fields:

11	9	12
IX1	IX2	OFFSET

• The IX1 field is the index in the first level page table
• The IX2 field is the index in the second level page table.
• The |IX1|IX2| concatenation defines the VPN (Virtual Page Number).

Two page sizes are supported:

• BPP : Big Physical Page / 2 Mbytes
• SPP : Small Physical pages / 4 Kbytes

unsigned long long _v2p_translate( unsigned int vaddr , unsigned int* flags )

This function returns the physical address from the virtual address. The MMU is supposed to be activated, and it uses the page table defined by the CP0_PTPR register. It supports both small (4 Kbytes) & big (2 Mbytes) pages.

• vaddr: virtual address.
• flags: page flags are returned in this variable.

Exit if PTE1 or PTE2 unmapped.