diff --git a/ci.md b/ci.md
index 88193ac..09439ab 100644
--- a/ci.md
+++ b/ci.md
@@ -117,7 +117,7 @@ au reset
 
 ## debug
 
-~Warning~ this is a hack.  But stepping through code is amazingly useful.  I have only tested it on Ubuntu; but should work on 
+*Warning* this is a hack.  But stepping through code is amazingly useful.  I have only worked out steps on Ubuntu 18.04, and depends on the simavr tool, which gives no uart output.  Still it is better than nothging.
 
 1. Install simavr (sudo apt install simavr).  This should also install avr-gcc.
 1. Install this toolset in in Ubunutu: run `au arduino` to spin up the basic working cache of the ide.