add sync support

README.sol2

@@ -46,3 +46,57 @@ create an /etc/ppp/ip-up script containing something like this:
 	/usr/sbin/ndd -set /dev/ip ip_forwarding 1
 
 See the man page for ip(7p) for details.
+
+Synchronous Serial Support.
+***************************
+
+This version has working but limited support for the on-board synchronous HDLC 
+interfaces. It has been tested with the /dev/se_hdlc and /dev/zsh drivers.
+Synchronous mode was tested with a Cisco router.
+
+There ppp daemon does not directly support controlling the serial interface.
+It relies on the /usr/sbin/syncinit command to initialize HDLC mode and 
+clocking.
+
+Some bugs remain: large sized frames are not sent/received properly, and
+may be related to the IP mtu. This
+may be due to bugs in pppd itself, bugs in Solaris or the serial drivers. 
+The /dev/zsh driver seems more larger and can send/receive larger frames
+than the /dev/se_hdlc driver. There is a confirmed bug with NRZ/NRZI mode
+in the /dev/se_hdlc driver, and Solaris patch 104596-11 is needed to correct
+it. (However this patch seems to introduce other serial problems. If you
+don't apply the patch, the workaround is to change the nrzi mode to yes or
+no, whichever works)
+
+How to start pppd with synchronous support:
+
+#!/bin/sh
+
+local=1.1.1.1   # your ip address here
+baud=38400	# needed, but ignored by serial driver
+
+# Change to the correct serial driver/port
+#dev=/dev/zsh0
+dev=/dev/se_hdlc0
+ 
+# Change the driver, nrzi mode, speed and clocking to match your setup
+# This configuration is for external clocking from the DCE
+connect="syncinit se_hdlc0 nrzi=no speed=64000 txc=rxc rxc=rxc"
+ 
+/usr/sbin/pppd $dev sync $baud novj noauth $local: connect "$connect"
+
+
+Sample Cisco router config excerpt:
+
+!
+! Cisco router setup as DCE with RS-232 DCE cable
+! 
+!         
+interface Serial0
+ ip address 1.1.1.2 255.255.255.0
+ encapsulation ppp
+ clockrate 64000
+ no nrzi-encoding
+ no shutdown
+!         
+