device,vga: add sync reg to update screen from software

src/device/device.c

@@ -9,10 +9,8 @@
 #define TIMER_HZ 100
 #define VGA_HZ 50
 
-static uint64_t jiffy = 0;
 static struct itimerval it;
 static int device_update_flag = false;
-static int update_screen_flag = false;
 
 void init_serial();
 void init_timer();
@@ -21,17 +19,12 @@ void init_i8042();
 
 extern void timer_intr();
 extern void send_key(uint8_t, bool);
-extern void update_screen();
 
 
 static void timer_sig_handler(int signum) {
-  jiffy ++;
   timer_intr();
 
   device_update_flag = true;
-  if (jiffy % (TIMER_HZ / VGA_HZ) == 0) {
-    update_screen_flag = true;
-  }
 
   int ret = setitimer(ITIMER_VIRTUAL, &it, NULL);
   Assert(ret == 0, "Can not set timer");
@@ -43,11 +36,6 @@ void device_update() {
   }
   device_update_flag = false;
 
-  if (update_screen_flag) {
-    update_screen();
-    update_screen_flag = false;
-  }
-
   SDL_Event event;
   while (SDL_PollEvent(&event)) {
     switch (event.type) {

src/device/vga.c

@@ -9,6 +9,8 @@
 
 #define SCREEN_PORT 0x100 // Note that this is not the standard
 #define SCREEN_MMIO 0x4100
+#define SYNC_PORT 0x104 // Note that this is not the standard
+#define SYNC_MMIO 0x4104
 #define SCREEN_H 300
 #define SCREEN_W 400
 
@@ -26,6 +28,12 @@ void update_screen() {
   SDL_RenderPresent(renderer);
 }
 
+static void vga_io_handler(uint32_t offset, int len, bool is_write) {
+  if (offset == 4 && len == 4 && is_write) {
+    update_screen();
+  }
+}
+
 void init_vga() {
   SDL_Init(SDL_INIT_VIDEO);
   SDL_CreateWindowAndRenderer(SCREEN_W * 2, SCREEN_H * 2, 0, &window, &renderer);
@@ -33,10 +41,10 @@ void init_vga() {
   texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_ARGB8888,
       SDL_TEXTUREACCESS_STATIC, SCREEN_W, SCREEN_H);
 
-  screensize_port_base = (void *)new_space(4);
-  *screensize_port_base = ((SCREEN_W) << 16) | (SCREEN_H);
-  add_pio_map("screen", SCREEN_PORT, (void *)screensize_port_base, 4, NULL);
-  add_mmio_map("screen", SCREEN_MMIO, (void *)screensize_port_base, 4, NULL);
+  screensize_port_base = (void *)new_space(8);
+  screensize_port_base[0] = ((SCREEN_W) << 16) | (SCREEN_H);
+  add_pio_map("screen", SCREEN_PORT, (void *)screensize_port_base, 8, vga_io_handler);
+  add_mmio_map("screen", SCREEN_MMIO, (void *)screensize_port_base, 8, vga_io_handler);
 
   vmem = (void *)new_space(0x80000);
   add_mmio_map("vmem", VMEM, (void *)vmem, 0x80000, NULL);