| 1 | = Virtual to Physical Address Translation = |
| 2 | |
| 3 | 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 used by the boot-loader and the kernel to implement the paged virtual memory. |
| 4 | |
| 5 | [PageOutline] |
| 6 | |
| 7 | 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. |
| 8 | |
| 9 | The virtual address format is 32 bits: structured in 3 fields: |
| 10 | || 11 || 9 || 12 || |
| 11 | || IX1 || IX2 || OFFSET || |
| 12 | * The IX1 field is the index in the first level page table |
| 13 | * The IX2 field is the index in the second level page table. |
| 14 | * The |IX1|IX2| concatenation defines the VPN (Virtual Page Number). |
| 15 | |
| 16 | Two page sizes are supported: |
| 17 | * BPP : Big Physical Page / 2 Mbytes |
| 18 | * SPP : Small Physical pages / 4 Kbytes |
| 19 | |
| 20 | === unsigned int _v2p_translate( page_table_t* pt, unsigned int vpn, unsigned int* ppn, unsigned int* flags ) === |
| 21 | |
| 22 | This function makes a VPN to PPN translation, from the page table defined by the ''pt'' pointer . The MMU is supposed to be activated. It supports both small (4 Kbytes) & big (2 Mbytes) pages. |
| 23 | It uses the address extension mechanism for physical addressing. |
| 24 | Return 0 if success. Return 1 if PTE1 or PTE2 unmapped. |
| 25 | |
| 26 | |