--- a/INSTALL	Thu Sep 28 17:51:17 2017 +0000
+++ b/INSTALL	Thu Sep 28 18:53:34 2017 +0000
@@ -57,6 +57,23 @@
 the functions that require access to Pirelli's IMEI have now been integrated
 into fc-fsio.
 
+libserial and Linux specifics
+=============================
+
+We have our own private library called libserial which contains our serial port
+handling code (serial ports are what we use to talk to Calypso GSM devices),
+and this library exists in several different versions.  At the top level of our
+source tree libserial is a symlink to one of libserial-* versions.
+
+Starting with fc-host-tools-r7, the default version of libserial (i.e., the
+version to which the libserial symlink points in the official release source)
+is libserial-newlnx.  This version of libserial has the advantage of supporting
+high GSM baud rates (see doc/High-speed-serial) with FTDI adapters without
+needing a dirty patch to the in-kernel driver, but it comes at the price of
+being very specific to Linux.  If you would like to run FreeCalypso host tools
+under FreeBSD, illumos or some other alternative-to-Linux OS, see the section
+titled "Support for other Unix flavors" in the doc/High-speed-serial article.
+
 Target binaries
 ===============