GIET_VM / System Calls

The stdio.c​ and stdio.h​ files define all system calls provided to user applications by the GIET-VM. They are generally prefixed by giet_.

All these functions use a syscall instruction to enter the system. In case of system call failure (illegal arguments), the syscall return value is -1 (0xFFFFFFFF), and the calling task is killed with a giet_exit().

Therefore, for all these system calls, the return value has not to be tested by the calling task.

1) Processor related system calls

void giet_proc_xyp( unsigned int* cluster_x, unsigned int* cluster_y unsigned int* lpid )

This function returns the processor identifiers (X,Y,P) from the wired global processor index in CP0_PROCID.

• cluster_x : X cluster coordinate
• cluster_y : Y cluster coordinate
• lpid : local processor index

No error possible, as the fixed format is gpid = ( ( cluster_x << Y_WIDTH + cluster_y ) << P_WIDTH ) + lpid

unsigned int giet_proctime()

This function returns the local processor time from the CP0_TIME register (number of cycles from reset). No error possible, as the processor implements a 32 bits wrapping register.

unsigned int giet_rand()

This function returns a pseudo-random value derived from both the CP0_PROCID and CP0_TIME registers. No error possible, as the return value is always between 0 & 65535.

2) Task related system calls

unsigned int giet_proc_task_id()

This functions returns (from the calling task context) the local task index, identifying the task amongst all task running on the same processor.

No error possible.

unsigned int giet_global_task_id()

This functions returns (from the calling task context) the global task id, unique in the system.

No error possible.

unsigned int giet_thread_id()

This functions returns (from the calling task context) the thread index, identiying the task in a given vspace.

No error possible.

3) TTY related system calls

The GIET_VM allows an user task to use a private TTY terminal, or to display log message on a shared TTY terminal.

void giet_tty_alloc()

This function allocates a private terminal to the calling task, and registers the terminal index in the task context. Task exit if no TTY terminal available.

void giet_tty_printf( char* format, ... )

This function print formated text on a private terminal that must have been allocated to the calling task in the mapping (use_tty argument). Therefore, it does not take the TTY lock. Only a limited number of formats are supported:

• %d : signed decimal
• %u : unsigned decimal
• %x : 32 bits hexadecimal
• %l : 64 bits hexadecimal
• %c : char
• %s : string

Task exit if private terminal index not defined, or in case of illegal format.

void giet_tty_getc( char* byte )

This blocking function fetches a single character from the private terminal that must have been allocated to the calling task in the application mapping. It uses the TTY_RX_IRQ interrupt, and the associated kernel buffer. Task exit if private TTY index not defined.

void giet_tty_getw( unsigned int* val )

This blocking function fetches a string of decimal characters (most significant digit first) to build a 32-bits unsigned integer from the private TTY terminal that must have been allocated to the calling task in the application mapping. It uses the TTY_RX_IRQ interrupt, and the associated kernel buffer. The non-blocking system function _tty_read is called several times, and the decimal characters are written in a 32 characters buffer until a <LF> character is read. It ignores non-decimal characters, and displays an echo for each decimal character. The <DEL> character is interpreted, and previous characters can be cancelled. When the <LF> character is received, the string is converted to an unsigned int value. If the number of decimal digit is too large for the 32 bits range, the zero value is returned. Task exit if private TTY index not defined.

void giet_tty_gets( char* buf, unsigned int bufsize )

This blocking function fetches a string from the private terminal that must have been allocated to the calling task in the application mapping. It writes the string to a fixed length buffer. It uses the TTY_RX_IRQ interrupt, and the associated kernel buffer. Up to (bufsize - 1) characters (including the non printable characters) are copied into buffer, and the string is completed by a NUL character. The <LF> character is interpreted, and the function close the string with a NUL character if <LF> is read. The <DEL> character is interpreted, and the corresponding character(s) are removed from the target buffer. It does not provide an echo. Task exit if private TTY index not defined.

void giet_shr_printf( char* format, ... )

This function print formated text on a shared terminal arbitrarily allocated by the kernel. It takes the TTY lock for exclusive access. It supports the same formats as the giet_tty_printf() function. Task exit in case of illegal format.

4) Timer related system calls

The GIET_VM allows an user task to activate a private timer channel, generating periodical IRQs. This timer is allocated in the external multi-timers peripheral.

void giet_timer_alloc( unsigned int period )

This function allocates a private user timer to the calling task, registers the channel index in the task context, and activates the timer. Task exit if no timer channel available

void giet_timer_stop( )

This function stops the private user timer allocated to the calling task.

5) File system related system calls

The Giet-VM supports a FAT32 file system.

int giet_fat_open( const char* pathname, unsigned int flags )

Open a file identified by the pathname argument. The read/write flags are not supported yet: no effect. Return -1 in case or error.

void giet_fat_read( unsigned int fd, void* buffer, unsigned int count, unsigned int offset )

Read count sectors from a file identified by the fd argument, skipping offset sectors in file, and writing into the user memory buffer. The user buffer base address should be 64 bytes aligned. In case or error, it makes a giet_exit().

void giet_fat_write( unsigned int fd, void* buffer, unsigned int count, unsigned int offset )

Write count sectors into a file identified by the fd argument, skipping offset sectors in file, and reading from the user memory buffer. The user buffer base address should be 64 bytes aligned. In case or error, it makes a giet_exit().

void giet_fat_close( unsigned int fd )

Close a file identified by the fd file descriptor.

6) Network related system calls

The GIET_VM allows a user task to directly access a private NIC channel.

unsigned int giet_nic_alloc( )

This function allocates a private NIC channel to the calling task, and returns the channel index.

Exit if no available NIC channel.

void giet_nic_sync_send( void* buffer )

This blocking function requires to transfer one container (4K bytes) from an user space buffer to the Ethernet Network Controller. It returns only when the container has been fully transfered. The buffer argument is the container base address in user space.

void giet_nic_sync_receive( void* buffer )

This blocking function requires to transfer one container (4K bytes) from the Ethernet Network Controller to an user space buffer. It returns only when the container has been fully transfered. The buffer argument is the container base address in user space.

7) Frame Buffer related system calls

An user task can access the frame buffer through a memcpy() or through the chained buffer DMA controller.

void giet_fb_sync_read( unsigned int offset, void* buffer, unsigned int length )

This blocking function use a memcopy strategy to transfer data from the frame buffer to an user buffer: offset defines the offset (in bytes) in the frame buffer, buffer is the user buffer base address, length is the number of bytes to be transfered.

void giet_fb_sync_write( unsigned int offset, void* buffer, unsigned int length )

This blocking function use a memcopy strategy to transfer data from an user buffer to the frame buffer: offset defines the offset (in bytes) in the frame buffer, buffer is the user buffer base address, length is the number of bytes to be transfered.

void giet_fbf_cma_start( void* buf0, void* buf1, unsigned int length )

This function initializes the chained buffer DMA controller (CMA) to transfer a stream of images from two user buffers to the frame buffer. It must be used in conjunction with the giet_fbf_cma_display() function. A CMA channel should have been allocated to the calling task in the application mapping.

• buf0( is the first user buffer base address
• buf1 is the second user buffer base address,
• length is the buffer size (bytes).

void giet_fbf_cma_display( unsigned int buffer )

This function enables the transfer of the buffer specified by the buffer argument (0 or 1).

void giet_fbf_cma_stop( )

This function desactivates the CMA channel allocated to the calling task.

8) Miscelaneous system calls

void giet_exit( char* string )

This function stops execution of the calling task with a TTY message explaining the cause. The user task is descheduled and becomes not runable: it does not consume processor cycles anymore.

void giet_assert( unsigned int condition, char* string )

This function uses the giet_exit() system call to kill the calling task if the condition is false.

void giet_context_switch()

The user task calling this function is descheduled and the processor is allocated to another task.

void giet_procnumber( unsigned int cluster_xy, unsigned int buffer )

This function returns in the buffer argument the number of processors in the cluster specified by the cluster_xy argument. In case or error (such as illegal cluster index), it makes a giet_exit().

void giet_vobj_get_vbase( char* vspace_name, char* vobj_name, unsigned int* vobj_vaddr)

This function returns in argument vobj_vaddr the virtual base address of a vobj defined in the mapping_info data structure. The vobj is identified by the two arguments vspace_name and vobj_name. In case of error (such as undefined vspace or undefined vobj), it makes a giet_exit().

void giet_heap_info( unsigned int* vaddr, unsigned int* length, unsigned int x, unsigned int y );

This function supports access to the running task's heap or to a remote heap. If (x < X_SIZE) and (y < Y_SIZE), it returns the base address and length of the heap associated to any task running on cluster(x,y). Otherwise, it returns the base address and length of the heap associated to the calling task. In case of error (such as undefined heap segment in the selected cluster, it returns heap_size = 0).

void giet_get_xy( void* ptr, unsigned int* px, unsigned int* py )

This function takes as input a virtual address (ptr argument), and returns through the px,py arguments the coordinates of the cluster containing the physical address associated to ptr. In case of error (unmapped virtual address), it makes a giet_exit().