diff --git a/user/diagdummy/diagdummy.c b/user/diagdummy/diagdummy.c
index fd2399e..f76bddc 100644
--- a/user/diagdummy/diagdummy.c
+++ b/user/diagdummy/diagdummy.c
@@ -1,7 +1,8 @@
 #include <ulib.h>
 
 #define CMDS(X)           \
-  X(block)      X(openf)
+  X(block)      X(openf)  \
+  X(serialprint)
 
 void main(void) {
   if (argslen() == 0) {
diff --git a/user/diagdummy/serial.c b/user/diagdummy/serial.c
new file mode 100644
index 0000000..df9288f
--- /dev/null
+++ b/user/diagdummy/serial.c
@@ -0,0 +1,21 @@
+#include <stdint.h>
+#include <stddef.h>
+#include <ulib.h>
+
+void diagdummy_serialprint(void) {
+  char *str = "Hello world\n";
+
+  if (argslen() >= 2) {
+    str = args()[1];
+  }
+
+  Dev_t serialdev;
+  dev_gethandle(&serialdev, "serialdev");
+
+  char *s = str;
+  while (*s) {
+    while(!dev_cmd(&serialdev, DEV_SERIALDEV_SENDREADY, NULL, 0));
+    dev_cmd(&serialdev, DEV_SERIALDEV_SENDB, s, 1);
+    s++;
+  }
+}