= GIET-VM / TTY0 access functions =

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The [source:soft/giet_vm/giet_common/tty0.c tty0.c] and [source:soft/giet_vm/giet_common/tty0.h tty0.h] files define the functions used to access the kernel terminal TTY[0]. The '''_put~''' functions do not take the lock protecting exclusive access to TTY0, and are used by the boot code. The '''_printf''' function takes the SBT lock protecting exclusive access to TTY0, and is used by the kernel code.

They are prefixed by "_" to remind that they can only be executed by a processor in kernel mode.

 === void '''_puts'''( char* string ) ===
Displays a ''string'' on kernel TTY0. This function does NOT take the TTY0 lock.

 === void '''_putx'''( unsigned int value ) ===
Displays a 32 bits word as an hexadecimal string on kernel TTY0. This function does NOT take the TTY0 lock.

=== void '''_putl'''( unsigned long long value ) ===
Displays a 64 bits word as an hexadecimal string on kernel TTY0. This function does NOT take the TTY0 lock.

 === void '''_putd'''( unsigned int value ) ===
Displays a 32 bits word as an decimal string on kernel TTY0. This function does NOT take the TTY0 lock.

 === void '''_getc'''( char* byte ) ===
This blocking function uses a polling strategy on the TTY0 status register to get a single character.

 === void '''_printf'''( char* format, ... ) ===
This function displays a formated string on TTY0, after taking the SBT lock to get exclusive access. Only the following formats are supported:
 * %s : character string (0 terminated)
 * %x : hexadecimal representation for an unsigned int (32 bits)
 * %l : hexadecimal representation for an unsigned long long (64 bits) 
 * %d : decimal representation for a signed int (32 bits)