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+Generic HDLC layer
+Krzysztof Halasa <khc@pm.waw.pl>
+January, 2003
+
+
+Generic HDLC layer currently supports:
+- Frame Relay (ANSI, CCITT and no LMI), with ARP support (no InARP).
+  Normal (routed) and Ethernet-bridged (Ethernet device emulation)
+  interfaces can share a single PVC.
+- raw HDLC - either IP (IPv4) interface or Ethernet device emulation.
+- Cisco HDLC,
+- PPP (uses syncppp.c),
+- X.25 (uses X.25 routines).
+
+There are hardware drivers for the following cards:
+- C101 by Moxa Technologies Co., Ltd.
+- RISCom/N2 by SDL Communications Inc.
+- and others, some not in the official kernel.
+
+Ethernet device emulation (using HDLC or Frame-Relay PVC) is compatible
+with IEEE 802.1Q (VLANs) and 802.1D (Ethernet bridging).
+
+
+Make sure the hdlc.o and the hardware driver are loaded. It should
+create a number of "hdlc" (hdlc0 etc) network devices, one for each
+WAN port. You'll need the "sethdlc" utility, get it from:
+        http://hq.pm.waw.pl/hdlc/
+
+Compile sethdlc.c utility:
+        gcc -O2 -Wall -o sethdlc sethdlc.c
+Make sure you're using a correct version of sethdlc for your kernel.
+
+Use sethdlc to set physical interface, clock rate, HDLC mode used,
+and add any required PVCs if using Frame Relay.
+Usually you want something like:
+
+        sethdlc hdlc0 clock int rate 128000
+        sethdlc hdlc0 cisco interval 10 timeout 25
+or
+        sethdlc hdlc0 rs232 clock ext
+        sethdlc hdlc0 fr lmi ansi
+        sethdlc hdlc0 create 99
+        ifconfig hdlc0 up
+        ifconfig pvc0 localIP pointopoint remoteIP
+
+In Frame Relay mode, ifconfig master hdlc device up (without assigning
+any IP address to it) before using pvc devices.
+
+
+Setting interface:
+
+* v35 | rs232 | x21 | t1 | e1 - sets physical interface for a given port
+                                if the card has software-selectable interfaces
+  loopback - activate hardware loopback (for testing only)
+* clock ext - external clock (uses DTE RX and TX clock)
+* clock int - internal clock (provides clock signal on DCE clock output)
+* clock txint - TX internal, RX external (provides TX clock on DCE output)
+* clock txfromrx - TX clock derived from RX clock (TX clock on DCE output)
+* rate - sets clock rate in bps (not required for external clock or
+                                 for txfromrx)
+
+Setting protocol:
+
+* hdlc - sets raw HDLC (IP-only) mode
+  nrz / nrzi / fm-mark / fm-space / manchester - sets transmission code
+  no-parity / crc16 / crc16-pr0 (CRC16 with preset zeros) / crc32-itu
+  crc16-itu (CRC16 with ITU-T polynomial) / crc16-itu-pr0 - sets parity
+
+* hdlc-eth - Ethernet device emulation using HDLC. Parity and encoding
+  as above.
+
+* cisco - sets Cisco HDLC mode (IP, IPv6 and IPX supported)
+  interval - time in seconds between keepalive packets
+  timeout - time in seconds after last received keepalive packet before
+            we assume the link is down
+
+* ppp - sets synchronous PPP mode
+
+* x25 - sets X.25 mode
+
+* fr - Frame Relay mode
+  lmi ansi / ccitt / none - LMI (link management) type
+  dce - Frame Relay DCE (network) side LMI instead of default DTE (user).
+  It has nothing to do with clocks!
+  t391 - link integrity verification polling timer (in seconds) - user
+  t392 - polling verification timer (in seconds) - network
+  n391 - full status polling counter - user
+  n392 - error threshold - both user and network
+  n393 - monitored events count - both user and network
+
+Frame-Relay only:
+* create n | delete n - adds / deletes PVC interface with DLCI #n.
+  Newly created interface will be named pvc0, pvc1 etc.
+
+* create ether n | delete ether n - adds a device for Ethernet-bridged
+  frames. The device will be named pvceth0, pvceth1 etc.
+
+
+
+
+Board-specific issues
+---------------------
+
+n2.o and c101.o need parameters to work:
+
+        insmod n2 hw=io,irq,ram,ports[:io,irq,...]
+example:
+        insmod n2 hw=0x300,10,0xD0000,01
+
+or
+        insmod c101 hw=irq,ram[:irq,...]
+example:
+        insmod c101 hw=9,0xdc000
+
+If built into the kernel, these drivers need kernel (command line) parameters:
+        n2.hw=io,irq,ram,ports:...
+or
+        c101.hw=irq,ram:...
+
+
+
+If you have a problem with N2 or C101 card, you can issue the "private"
+command to see port's packet descriptor rings (in kernel logs):
+
+        sethdlc hdlc0 private
+
+The hardware driver has to be build with CONFIG_HDLC_DEBUG_RINGS.
+Attaching this info to bug reports would be helpful. Anyway, let me know
+if you have problems using this.
+
+For patches and other info look at http://hq.pm.waw.pl/hdlc/