diff --git a/earth/earth.c b/earth/earth.c
index 4e012a6c..b788c278 100644
--- a/earth/earth.c
+++ b/earth/earth.c
@@ -24,7 +24,7 @@ int main() {
 
     /* Put earth interface to a widely known address */
     memcpy((void*)EARTH_ADDR, &earth, sizeof(earth));
-    INFO("Put earth interface at 0x%.8x with size %d", EARTH_ADDR, sizeof(earth));
+    INFO("Put earth interface at 0x%.8x with size 0x%x", EARTH_ADDR, sizeof(earth));
 
     INFO("Start to load the grass layer");
     return 0;
@@ -59,5 +59,11 @@ int earth_init() {
     earth.intr_register = intr_register;
     SUCCESS("Finished initializing the CPU interrupts");
 
+    earth.log.log_info = INFO;
+    earth.log.log_highlight = HIGHLIGHT;
+    earth.log.log_success = SUCCESS;
+    earth.log.log_error = ERROR;
+    earth.log.log_fatal = FATAL;
+
     return 0;
 }
diff --git a/grass/grass.c b/grass/grass.c
index bc315132..3bfa586e 100644
--- a/grass/grass.c
+++ b/grass/grass.c
@@ -8,7 +8,10 @@
  * spawns some kernel processes, including file system and shell
  */
 
-#include <stdlib.h>
+#include "egos.h"
+#include "grass.h"
+
+struct earth *earth = (void*)EARTH_ADDR;
 
 int global_var1;
 int global_var2;
@@ -21,5 +24,6 @@ int main() {
 
     char* buf = malloc(512);
     free(buf);
+    SUCCESS("Within grass kernel with stack variable @0x%.8x", &buf);
     return 0;
 }
diff --git a/grass/grass.h b/grass/grass.h
new file mode 100644
index 00000000..bea60e14
--- /dev/null
+++ b/grass/grass.h
@@ -0,0 +1,12 @@
+#pragma once
+
+#include <stdlib.h>
+
+extern struct earth *earth;
+#define printf    earth->tty_write
+
+#define INFO      earth->log.log_info
+#define HIGHLIGHT earth->log.log_highlight
+#define SUCCESS   earth->log.log_success
+#define ERROR     earth->log.log_error
+#define FATAL     earth->log.log_fatal
diff --git a/shared/include/egos.h b/shared/include/egos.h
index f2aedda2..11f99ef2 100644
--- a/shared/include/egos.h
+++ b/shared/include/egos.h
@@ -1,14 +1,24 @@
 #pragma once
 
+/* Interface between earth and grass */
+
 #define TIMER_INTR_ID   7
 #define QUANTUM_NCYCLES 2000
 #define EARTH_ADDR      (0x8004000 - 0x40)
 
 typedef void (*handler_t)(int, void*);
 
+struct dev_log {
+    int (*log_info)(const char *format, ...);
+    int (*log_highlight)(const char *format, ...);
+    int (*log_success)(const char *format, ...);
+    int (*log_error)(const char *format, ...);
+    int (*log_fatal)(const char *format, ...);
+};
+
 struct earth {
     int (*tty_read)(char* buf, int len);
-    int (*tty_write)(const char *format, ...);    
+    int (*tty_write)(const char *format, ...);
 
     int (*disk_read)(int block_no, int nblocks, char* dst);
     int (*disk_write)(int block_no, int nblocks, char* src);
@@ -16,4 +26,8 @@ struct earth {
     int (*intr_enable)();
     int (*intr_disable)();
     int (*intr_register)(int id, handler_t handler);
+
+    struct dev_log log;
 };
+
+/* Interface between grass and apps */