--- a/doc/RVTMUX	Sat Nov 03 05:51:17 2018 +0000
+++ b/doc/RVTMUX	Sun Nov 04 01:55:35 2018 +0000
@@ -1,3 +1,13 @@
+[Historical note: this document was originally written in 2014 when the vision
+ of FreeCalypso was very different from what it is today.  Since then we have
+ transitioned from making aftermarket hacks on pre-existing Calypso phones and
+ modems to producing and supporting our own FreeCalypso hardware products, and
+ our firmware work has changed from a nebulous dream to stable production code.
+ The ways in which we approach various technical aspects have changed
+ accordingly, but much of our documentation has been slow to catch up.  The
+ documentation is now being updated, but there may still be some passages where
+ the old world view shines through.]
+
 TI's Calypso GSM/GPRS baseband processor chip has not one but two UART serial
 ports, called "MODEM" and "IrDA" in the hardware documentation.  In hardware
 terms, both support basic data-leads-only UART operation at a fixed baud rate,