This is a description how I understand the difference between net and character drivers for HDLC:
The HDLC is basically a L2 protocol used to carry frames over a synchronous channel like a timeslot/group of timeslots on a TDM interface (it is used in modem protocols too but it is off-topic here). The HDLC protocol can be used therefore as a lower sublayer for synchronous-PPP or Cisco HDLC or Frame Relay (or X.25) protocol. A specific hardware-based HDLC driver in Linux is connected then to a generic upper-sublayer HDLC driver which takes care on frame headers, service frames and timers. The sources of the generic driver and some particular lower-level (HW-dependant) drivers are in /linux/drivers/net/wan/ The net driver for MPC860 is available from our web-site. Additionally the HDLC protocol is widely used in telecommunication protocols like ISDN, V5.1,V5.2, GR.303 and SS-7. It can be also used for internal communication inside a phone switch etc. Usually the upper layer is LAP-D. It can be easier to implement the processing of these protocols in User Space than in kernel. The simpliest way of presenting raw framed data to User Space (in Linux) is using read/write/(poll or fasync) methods on a character device inode. This is probably the reason why the driver https://sourceforge.net/projects/mcc8260/ is a character one. NB. I was not aware of this project and I've developed my own (very simple) character-device driver for HDLC/transparent channels on 8260 MCC. Many thanks to mailto:omanakuttan at tataelxsi.co.in for his howto and his help! Now the driver is finished and will be released under GPL soon, after passing tests. If someone wants to see the code now, please let me know. If someone wants to wrap the driver to fit into the "net" domain, I can advice how to do it. Regards, Adam ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
