drivers: add up/down scrolling thru VGA screens

Signed-off-by: Pawel Wieczorkiewicz <[email protected]>

Author: wipawel

drivers/vga.c

@@ -30,6 +30,7 @@
 #define MAX_ROWS VGA_ROWS
 #define MAX_COLS (2 * VGA_COLS)
 
+static unsigned scroll_screen = 0;
 
 static uint8_t vga_buffer[VGA_SCREENS][MAX_ROWS][MAX_COLS];
 
@@ -39,6 +40,16 @@ static inline void write_vga_buffer(int cur_screen) {
     memcpy(vga_memory, vga_buffer[cur_screen], sizeof(vga_buffer[cur_screen]));
 }
 
+void vga_scroll_down(void) {
+    if (scroll_screen < (VGA_SCREENS - 1))
+        write_vga_buffer(++scroll_screen);
+}
+
+void vga_scroll_up(void) {
+    if (scroll_screen > 0)
+        write_vga_buffer(--scroll_screen);
+}
+
 void vga_write(const char *buf, size_t len, vga_color_t color) {
     static int screen = 0, row = 0, col = 0;
 
@@ -65,5 +76,6 @@ void vga_write(const char *buf, size_t len, vga_color_t color) {
         vga_buffer[screen][row][col++] = color;
     }
 
+    scroll_screen = screen;
     write_vga_buffer(screen);
 }

include/drivers/vga.h

@@ -55,5 +55,8 @@ typedef enum vga_color vga_color_t;
 #define VGA_COLS       80
 #define VGA_SCREENS    10
 
+extern void vga_scroll_up(void);
+extern void vga_scroll_down(void);
+
 extern void vga_write(const char *buf, size_t len, vga_color_t color);
 #endif /* KTF_DRV_VGA_H */