= GIET-VM / Miscelaneous common kernel functions =

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The [source:soft/giet_vm/giet_common/utils.c utils.c] and [source:soft/giet_vm/giet_common/utils.h utils.h] files define various kernel functions that can be used by both the kernel code and the boot code.

=== void '''_exit'''(void) ===
This function is called in case of kernel error.
The processor try to displays an error message on TTY0, and suicide (enter infinite loop)...

=== void '''_random_wait'''( unsigned int value ) ===
This function implements a pseudo-random delay.
The 5 LSB bits of the '''value''' argument (number between 0 and 31) define the average delay value: 2 * (2**(value[4:0]

=== void '''_break'''( char* str ) ===
This function can be used for interactive kernel debug. It displays the '''str''' string on TTY0,
and waits until a character typed on TTY0.

=== unsigned int '''_strncmp'''( const char*  s1, const char*  s2,  unsigned int n );
This function compares the '''n''' first characters of the two '''s1''' and '''s2''' strings.
Returns 0 if all characters are identical. returns 1 otherwise.

=== char* '''_strcpy'''( char* dest,  char* source ) ===
This function copies the '''source''' string to the '''dest''' string, and returns a pointer on the '''dest''' string. 

=== void '''_dcache_buf_invalidate'''( unsigned int buf_vbase,  unsigned int buf_size ) ===
This function invalidates all cache lines contained in the L1 data cache that overlap the buffer defined by
the '''buf_vbase''' and '''buf_size''' arguments.

=== void '''_get_sbt_footprint'''( unsigned int* width,  unsigned int* heigth,  unsigned int* levels ) ===
A Sliced Binary Tree (SBT) can be used to implement a scalable, distributed synchronisation, such as a sbt_barrier or a sbt_lock. This function computes the footprint of the smallest SBT  covering all clusters containing processors in a platform. The SBT footprint is defined by the '''width''' and  '''heigth''' parameters. The '''levels''' parameter define the number of levels between the root and the leaves, with the following constraints:
 * cluster[0][0] is always covered by the SBT
 * the number of clusters in a row (width) is always power of 2
 * the number of xlusters in a column (heigth) is always power of 2
 * (width = heigth) OR (width = 2 * heigth)
The width/heigth parameters can be larger than the X_SIZE/Y_SIZE parameters, when X_SIZE or Y_SIZE are not power of 2. The width/heigth parameters can be smaller than the X_SIZE/Y_SIZE parameters, when the upper row, or the right column of clusters does not contain processors.