Add get_frame_counter() method to VGA module interface.

src/main.c

@@ -29,7 +29,7 @@ int main()
 	for (;;)
 	{
 		// moving sine
-		const uint16_t fc = frame_counter;
+		const uint16_t fc = vga_get_frame_counter();
 		const uint16_t x = fc % 640;
 		const uint16_t y = 380 + 100 * (abs(320 - x) / 640.0) * sin((fc % 640) / 12.738);
 

src/vga.c

@@ -26,7 +26,7 @@ static PIORun vga_hsync, vga_vsync, vga_pixel;
 static bool dma_ready = false;
 static int dma_channel;
 
-unsigned long int frame_counter = 0;
+static unsigned long int frame_counter = 0;
 
 static void setup_clocks(void)
 {
@@ -213,3 +213,8 @@ void vga_machines_init(void)
 
 	printf("Now running.\n");
 }
+
+unsigned long int vga_get_frame_counter(void)
+{
+	return frame_counter;
+}

src/vga.h

@@ -2,7 +2,6 @@
 #define VGA_H
 
 void vga_machines_init(void);
-
-extern unsigned long int frame_counter;
+unsigned long int vga_get_frame_counter(void);
 
 #endif // VGA_H