UM0851 datasheet(115/245 Pages) STMICROELECTRONICS

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UM0851

Communication device drivers

Doc ID 16604 Rev 2

115/245

Figure 30.

Data structure layers

●

port_t: physical interface abstraction, SPEAr HDLC driver specified structure. It keeps

track of all the HDLC channels running on this interface. TDM/E1 interfaces may have

multiple HDLC channels. RS485 interface only has one HDLC channel.

●

channel_t: logical HDLC channel abstraction, SPEAr HDLC driver specified structure.

Derived from hdlc_device structure. It contains a pointer to the physical interfaces it

belongs to.

●

hdlc_device: common HDLC device defined in the generic HDLC layer, derived from

net_device

●

net_device: common network device defined in the Linux network layer.

4.10.3

SPEAr HDLC driver interface

The SPEAr HDLC driver uses common network device interfaces. The generic HDLC layer

provides common routines to interact with the Linux network layer. The SPEAr HDLC driver

calls the generic HDLC layer to register itself and handle any common requests.

Init HDLC channels

When the driver module is loaded, spr_hdlc_add_port() is called for each physical port to be

initialized and registers the corresponding HDLC channels.

For TDM/E1 port, multiple HDLC channel is registered. The number of HDLC channels is

defined in configuration CONFIG_SPEAR_TDM_HDLC_CHANNEL_NUM. For each RS485

port, one HDLC channel is registered.

For every HDLC channel, one SPEAr HDLC private structure channel_t is created. The

driver also creates a common HDLC device structure by calling alloc_hdlcdev in Linux

generic HDLC layer. Then, it associates it with the channel_t structure. The prototype of

alloc_hdlcdev is:

struct net_device *alloc_hdlcdev(void *priv);

/* Driver passes the SPEAR HDLC priavte structure channel_t to the priv argument

It returns a standard net_device structure pointer.

The access to hdlcdev structure is done via macros struct hdlc_dev

*hdev = dev_to_hdlc(dev);

The access to the SPEAR HDLC private structure is done via casting the priv member

of hdlc_dev struct channel_t *ch = dev_to_hdlc(dev)->priv; */

net_device

port_t

SPEAr

HDLC

Driver

hdlc_device

channel_t

Network

Layer

Generic

HDLC

Layer

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