CHAPTER 6. DEVELOPING ESSENTIAL DEVICE DRIVERS AND A
FILESYSTEM 70
int i;
for (i=0; i<no_bytes; i++) {
*(dest + i) = *( source + i);
}
}Now we can usememorycopy, as in Figure XXX, to scroll our screen./* Advance the text cursor , scrolling the video buffer if necessary. */
int handle_scrolling(int cursor_offset) {// If the cursor is within the screen , return it unmodified.
if (cursor_offset < MAX_ROWS*MAX_COLS *2) {
return cursor_offset;
}/* Shuffle the rows back one. */
int i;
for (i=1; i<MAX_ROWS; i++) {
memory_copy(get_screen_offset (0,i) + VIDEO_ADDRESS ,
get_screen_offset (0,i-1) + VIDEO_ADDRESS ,
MAX_COLS *2
);
}/* Blank the last line by setting all bytes to 0 */
char* last_line = get_screen_offset (0,MAX_ROWS -1) + VIDEO_ADDRESS;
for (i=0; i < MAX_COLS *2; i++) {
last_line[i] = 0;
}// Move the offset back one row , such that it is now on the last
// row , rather than off the edge of the screen.
cursor_offset -= 2* MAX_COLS;
// Return the updated cursor position.
return cursor_offset;
}