diff --git a/notes-from-r1.txt b/notes-from-r1.txt
index 3e0d7cc..5b9d81b 100644
--- a/notes-from-r1.txt
+++ b/notes-from-r1.txt
@@ -14,3 +14,4 @@
  - need p channel mosfets for most switches :(
  - tie 3v3 reg mode to a gpio
  - replace analog ldo with filtering caps for high noise
+ - ESP32 only support to set GPIO0/GPIO1/GPIO3 as mclk signal