student-distrib/system_call.c
int syscall_vidmap(uint8_t ** screen_start){
	if ( screen_start == NULL || screen_start == (uint8_t **)fourM)
		return -1;
	//148MB is the user video page location 
	videomem_map(_148MB, video_mem_addr);
	*screen_start = (uint8_t*) _148MB ;

	 return 0;

}
/* syscall_vidmap
 * Input: user ptr to a ptr to be assigned vidmem
 * Returns: -1 if cannot be execute
 * Effect: allocate user_level video_mem
 */
syscall_vidmap
Input: user ptr to a ptr to be assigned vidmem
Returns: -1 if cannot be execute
Effect: allocate user_level video_mem
syscall_vidmap Input : user ptr to a ptr to be assigned vidmem Returns : - 1 if cannot be execute Effect : allocate user_level video_mem
int syscall_vidmap(uint8_t ** screen_start){
	if ( screen_start == NULL || screen_start == (uint8_t **)fourM)
		return -1;
	videomem_map(_148MB, video_mem_addr);
	*screen_start = (uint8_t*) _148MB ;
	 return 0;
}
int syscall_vidmap ( uint8_t * * screen_start ) { if ( screen_start == NULL || screen_start == ( uint8_t * * ) fourM ) return -1 ; videomem_map ( _148MB , video_mem_addr ) ; * screen_start = ( uint8_t * ) _148MB ; return 0 ; }
syscall_vidmap
 Input: user ptr to a ptr to be assigned vidmem
 Returns: -1 if cannot be execute
 Effect: allocate user_level video_mem
syscall_vidmap Input : user ptr to a ptr to be assigned vidmem Returns : - 1 if cannot be execute Effect : allocate user_level video_mem
//148MB is the user video page location 