= Virtual to Physical Address Translation =

The [source:soft/giet_vm/giet_common/vmem.c vmem.c] and [source:soft/giet_vm/giet_common/vmem.h vmem.h] files define the data structures and functions used by the boot-loader and the kernel to implement the paged virtual memory.

[[PageOutline]]

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.