= 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.

=== void '''_v2p_add_pte1'''( unsigned int vspace_id , unsigned int x , unsigned int y , unsigned int vpn , unsigned int flags , unsigned int ppn , unsigned int ident ) ===
This function registers a new PTE1 (BPP)vin the page table defined by the <vspace_id> argument, and the <x,y> coordinates. The value is defined by the <flags> and <ppn> arguments.
It updates only the first level PT1. As each vseg is mapped by a different processor, the PT1 entry cannot be concurrently accessed, and we don't need to take any lock.

=== void '''_v2p_add_pte2'''( unsigned int vspace_id , unsigned int x , unsigned int y , unsigned int vpn ) ===

=== void '''_v2p_del_pte1'''( unsigned int vspace_id , unsigned int x , unsigned int y , unsigned int vpn ) ===

=== void '''_v2p_del_pte2'''( unsigned int vspace_id , unsigned int x , unsigned int y , unsigned int vpn ) ===