add fb_ready()

src/fb.c

@@ -1,4 +1,5 @@
 #include "fb.h"
+#include <stddef.h>
 
 static uint32_t * fb;
 static uint32_t fb_width;
@@ -28,3 +29,8 @@ void fb_init(uint32_t * addr, uint32_t width, uint32_t height, uint32_t pitch)
         }
     }
 }
+
+bool fb_ready(void)
+{
+    return fb != NULL;
+}

src/fb.h

@@ -2,7 +2,9 @@
 #define FB_H
 
 #include <stdint.h>
+#include <stdbool.h>
 
 void fb_init(uint32_t * addr, uint32_t width, uint32_t height, uint32_t pitch);
+bool fb_ready(void);
 
 #endif

src/hos_main.c

@@ -5,4 +5,8 @@
 void hos_main(uint32_t mbinfo_addr)
 {
     mbinfo_init(mbinfo_addr);
+    if (!fb_ready())
+    {
+        return;
+    }
 }