Change bootstub POST codes to B0B0 (enter) and EEEE (fail).

The bootstub was emitting C0DE at entry and DEAD for failure. With only an
8-bit POST code monitor attached to port 80, it is not immediately clear
whether "DE" is from the entry point or the failure point.

B0 and EE are not currently used in x86 BIOS, AFAIK.


Change-Id: I86448019655b39c40b197724ad200a659c142b80
Reviewed-by: Randall Spangler <>
Tested-by: Bill Richardson <>
diff --git a/bootstub.c b/bootstub.c
index 85aa219..6f5d417 100644
--- a/bootstub.c
+++ b/bootstub.c
@@ -182,7 +182,7 @@
     void *guid_ptr;
     // I'm here.
-    port80w(0xc0de);
+    port80w(0xb0b0);
     // Find the parameters that the BIOS has passed to us.
     if (uefi_call_wrapper(systab->BootServices->HandleProtocol, 3,
@@ -246,7 +246,7 @@
     // Bad Things happened.
-    port80w(0xdead);
+    port80w(0xeeee);
     return EFI_LOAD_ERROR;