= Kernel Utilities =

The [source:soft/giet_vm/giet_common/utils.c utils.c] and [source:soft/giet_vm/giet_common/utils.h util.h] files define useful kernel functions, that are used both by the boot_loader and by the kernel. 
They are prefixed by ''_'' to remind that they can only be executed by a processor in kernel mode.

 * They are used by the boot-loader in the ''static'' phase, to build the page tables and initialize the schedulers and the peripherals.
 * They are also used by the kernel in the ''dynamic'' phase, to handle events such as interrupts, exceptions and syscalls. 

[[PageOutline]]

 == __1) CP0 registers access functions__ ==

 === unsigned int _get_sched( void ) ===
Returns the virtual address of the scheduler, stored in the CP0_SCHED register, for the processor running the calling task. 

 === unsigned int _get_epc( void ) ===
Returns the value stored in the CP0_EPC register, for the processor running the calling task.  

 === unsigned int _get_cr( void ) ===
Returns the value stored in the CP0_CR register, for the processor running the calling task. 

 === unsigned int _get_sr( void ) ===
Returns the value stored in the CP0_SR register, for the processor running the calling task. 

 === unsigned int _get_bvar( void ) ===
Returns the value stored in the CP0_BVAR register, for the processor running the calling task. 

 === unsigned int _get_procid( void ) ===
Returns the global processor identifier stored in the CP0_PROCID register for the processor running the calling task. 

 === unsigned int _get_protime( void ) ===
Returns the cycle count stored in the CP0_TIME register for the processor running the calling task. 

 === void _set_sched( unsigned int value ) ===
Writes ''value'' in the CP0_SCHED register, for the processor running the calling task. 

 === void _set_sr( unsigned int value ) ===
Writes ''value'' in the CP0_SR register, for the processor running the calling task. 

 === void _it_disable( unsigned int* save_sr_ptr ) ===
Disables interrupts for the processor running the calling task and save the CP0_SR value at address ''save_sr_ptr''.

 === void _it_restore( unsigned int* save_sr_ptr ) ===
Writes the value pointed by ''save_sr_ptr'' into the CP0_SR register, for the processor running the calling task.

 == __2) CP2 registers access functions__ ==

 === unsigned int _get_mmu_ptpr( void ) ===
Returns the value stored in the CP2_PTPR register, for the processor running the calling task.

 === unsigned int _get_mmu_mode( void ) ===
Returns the value stored in the CP2_MODE register, for the processor running the calling task.

 === void _set_mmu_ptpr( unsigned int value ) ===
Writes ''value'' in the CP2_PTPR register, for the processor running the calling task.

 === void _set_mmu_mode( unsigned int value ) ===
Writes ''value'' in the CP2_MODE register, for the processor running the calling task.

 == __3) Physical addressing functions__ ==

 === unsigned int _physical_read( unsigned long long paddr ) ===
Returns the 32 bits word stored at physical address ''paddr'', after a temporary DTLB deactivation.
It uses the CP2_PADDR_EXT register.

 === void _physical_write( unsigned long long paddr, unsigned int value )
Writes the 32 bits word ''value'' at physical address ''paddr'', after a temporary DTLB deactivation.
It uses the CP2_PADDR_EXT register.

 === unsigned long long _physical_read_ull( unsigned long long paddr ) ===
Returns the 64 bits word stored at physical address ''paddr'', after a temporary DTLB deactivation.
It uses the CP2_PADDR_EXT register.

 === void _physical_write_ull( unsigned long long paddr, unsigned long long value ) ===
Writes the 64 bits word ''value'' at physical address ''paddr'', after a temporary DTLB deactivation.
It uses the CP2_PADDR_EXT register.

 === void _physical_memcpy( unsigned long long dst_paddr, unsigned long long src paddr, unsigned int size ) ===
This function makes a memcpy from a source buffer to a destination buffer, using physical addresses, after a temporary DTLB de-activation. The ''src_paddr'', ''dst_paddr'' and ''size'' arguments must be multiple of 4 bytes. 

 === unsigned int _io_extended_read( unsigned int* vaddr ) ===
This function is used by the GIET-VM drivers to read a 32 bits word in a peripheral register.
If the MMU is not activated, the virtual address is extended using X_IO and Y_IO (defined in the hard-config.h file) to reach the cluster_io.

 === void _io_extended_write( unsigned int* vaddr, unsigned int value ) ===
This function is used by the GIET-VM drivers to write a 32 bits word in a peripheral register.
If the MMU is not activated, the virtual address is extended using X_IO and Y_IO (defined in the hard-config.h file) to reach the cluster_io.

 == __X) Miscelaneous functions__ ==