--- a/Tango-pinmux	Sat Jul 17 17:01:39 2021 +0000
+++ b/Tango-pinmux	Sat Jul 17 17:19:00 2021 +0000
@@ -120,6 +120,19 @@
 that is configured as a generic (not built-in function) output can be set with
 AT+IOW.
 
+Programming /etc/tango-pinmux
+=============================
+
+To program the pinmux config file on a Tango module running any of our official
+FreeCalypso firmware versions, you will need to use FC host tools.  Connect to
+the RVTMUX debug trace and control interface (second UART) via rvinterf and
+execute the following command in fc-fsio:
+
+fwrite /etc/tango-pinmux hex "xx xx xx xx"
+
+Replace xx placeholders inside the double quotes with the 4 hex bytes to be
+programmed; the double quotes are required.
+
 Other GPIO pins
 ===============