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><H1
><A
NAME="IO-ETH-DRV-GENERIC1">Chapter 46. Generic Ethernet Device Driver</H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
><A
HREF="io-eth-drv-generic1.html#IO-ETH-DRV-API"
>Generic Ethernet API</A
></DT
><DT
><A
HREF="io-eth-drv-api-funcs.html"
>Review of the functions</A
></DT
><DT
><A
HREF="io-eth-drv-upper-api.html"
>Upper Layer Functions</A
></DT
><DT
><A
HREF="io-eth-call-graph.html"
>Calling graph for Transmission and Reception</A
></DT
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="IO-ETH-DRV-API">Generic Ethernet API</H1
><P
>This file provides a simple description of how to write a low-level,
hardware dependent ethernet driver.</P
><P
>There is a high-level driver (which is only code — with no state of
its own) that is part of the stack. There will be one or more low-level
drivers tied to the actual network hardware. Each of these drivers
contains one or more driver instances. The intent is that the
low-level drivers know nothing of the details of the stack that will be
using them. Thus, the same driver can be used by the
<SPAN
CLASS="PRODUCTNAME"
>eCos</SPAN
>
supported
<SPAN
CLASS="ACRONYM"
>TCP/IP</SPAN
>
stack,
<SPAN
CLASS="PRODUCTNAME"
>RedBoot</SPAN
>,
or any other, with no changes.</P
><P
>A driver instance is contained within a
<SPAN
CLASS="TYPE"
>struct eth_drv_sc</SPAN
>:
<TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>struct eth_hwr_funs {
// Initialize hardware (including startup)
void (*start)(struct eth_drv_sc *sc,
unsigned char *enaddr,
int flags);
// Shut down hardware
void (*stop)(struct eth_drv_sc *sc);
// Device control (ioctl pass-thru)
int (*control)(struct eth_drv_sc *sc,
unsigned long key,
void *data,
int data_length);
// Query - can a packet be sent?
int (*can_send)(struct eth_drv_sc *sc);
// Send a packet of data
void (*send)(struct eth_drv_sc *sc,
struct eth_drv_sg *sg_list,
int sg_len,
int total_len,
unsigned long key);
// Receive [unload] a packet of data
void (*recv)(struct eth_drv_sc *sc,
struct eth_drv_sg *sg_list,
int sg_len);
// Deliver data to/from device from/to stack memory space
// (moves lots of memcpy()s out of DSRs into thread)
void (*deliver)(struct eth_drv_sc *sc);
// Poll for interrupts/device service
void (*poll)(struct eth_drv_sc *sc);
// Get interrupt information from hardware driver
int (*int_vector)(struct eth_drv_sc *sc);
// Logical driver interface
struct eth_drv_funs *eth_drv, *eth_drv_old;
};
struct eth_drv_sc {
struct eth_hwr_funs *funs;
void *driver_private;
const char *dev_name;
int state;
struct arpcom sc_arpcom; /* ethernet common */
};</PRE
></TD
></TR
></TABLE
></P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>If you have two instances of the same hardware, you only need one
<SPAN
CLASS="TYPE"
>struct eth_hwr_funs</SPAN
> shared between them.</P
></BLOCKQUOTE
></DIV
><P
>There is another structure which is used to communicate with the rest of
the stack:
<TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>struct eth_drv_funs {
// Logical driver - initialization
void (*init)(struct eth_drv_sc *sc,
unsigned char *enaddr);
// Logical driver - incoming packet notifier
void (*recv)(struct eth_drv_sc *sc,
int total_len);
// Logical driver - outgoing packet notifier
void (*tx_done)(struct eth_drv_sc *sc,
CYG_ADDRESS key,
int status);
};</PRE
></TD
></TR
></TABLE
>
Your driver does <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> create an instance of this
structure. It is provided for driver code to use in the
<SPAN
CLASS="TYPE"
>eth_drv</SPAN
> member of the function record.
Its usage is described below in <A
HREF="io-eth-drv-upper-api.html"
>the Section called <I
>Upper Layer Functions</I
></A
></P
><P
>One more function completes the API with which your driver communicates
with the rest of the stack:
<TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>extern void eth_drv_dsr(cyg_vector_t vector,
cyg_ucount32 count,
cyg_addrword_t data);</PRE
></TD
></TR
></TABLE
></P
><P
>This function is designed so that it can be registered as the DSR for your
interrupt handler. It will awaken the
“Network Delivery Thread”
to call your deliver routine. See <A
HREF="io-eth-drv-api-funcs.html#IO-ETH-DRV-API-DELIVER"
>the Section called <I
>Deliver function</I
></A
>.</P
><P
>You create an instance of <SPAN
CLASS="TYPE"
>struct eth_drv_sc</SPAN
>
using the
<TT
CLASS="FUNCTION"
>ETH_DRV_SC()</TT
>
macro which
sets up the structure, including the prototypes for the functions, etc.
By doing things this way, if the internal design of the ethernet drivers
changes (e.g. we need to add a new low-level implementation function),
existing drivers will no longer compile until updated. This is much
better than to have all of the definitions in the low-level drivers
themselves and have them be (quietly) broken if the interfaces change.</P
><P
>The “magic”
which gets the drivers started (and indeed, linked) is
similar to what is used for the I/O subsystem.
This is done using the
<TT
CLASS="FUNCTION"
>NETDEVTAB_ENTRY()</TT
>
macro, which defines an initialization function
and the basic data structures for the low-level driver.</P
><P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> typedef struct cyg_netdevtab_entry {
const char *name;
bool (*init)(struct cyg_netdevtab_entry *tab);
void *device_instance;
unsigned long status;
} cyg_netdevtab_entry_t;</PRE
></TD
></TR
></TABLE
>
The <TT
CLASS="VARNAME"
>device_instance</TT
>
entry here would point to the <SPAN
CLASS="TYPE"
>struct eth_drv_sc</SPAN
>
entry previously defined. This allows the network driver
setup to work with any class of driver, not just ethernet drivers. In
the future, there will surely be serial <SPAN
CLASS="ACRONYM"
>PPP</SPAN
>
drivers, etc. These will
use the <TT
CLASS="FUNCTION"
>NETDEVTAB_ENTRY()</TT
>
setup to create the basic driver, but they will
most likely be built on top of other high-level device driver layers.</P
><P
>To instantiate itself, and connect it to the system,
a hardware driver will have a template
(boilerplate) which looks something like this:
<TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>#include <cyg/infra/cyg_type.h>
#include <cyg/hal/hal_arch.h>
#include <cyg/infra/diag.h>
#include <cyg/hal/drv_api.h>
#include <cyg/io/eth/netdev.h>
#include <cyg/io/eth/eth_drv.h>
ETH_DRV_SC(<TT
CLASS="REPLACEABLE"
><I
>DRV</I
></TT
>_sc,
0, // No driver specific data needed
"eth0", // Name for this interface
<TT
CLASS="REPLACEABLE"
><I
>HRDWR</I
></TT
>_start,
<TT
CLASS="REPLACEABLE"
><I
>HRDWR</I
></TT
>_stop,
<TT
CLASS="REPLACEABLE"
><I
>HRDWR</I
></TT
>_control,
<TT
CLASS="REPLACEABLE"
><I
>HRDWR</I
></TT
>_can_send
<TT
CLASS="REPLACEABLE"
><I
>HRDWR</I
></TT
>_send,
<TT
CLASS="REPLACEABLE"
><I
>HRDWR</I
></TT
>_recv,
<TT
CLASS="REPLACEABLE"
><I
>HRDWR</I
></TT
>_deliver,
<TT
CLASS="REPLACEABLE"
><I
>HRDWR</I
></TT
>_poll,
<TT
CLASS="REPLACEABLE"
><I
>HRDWR</I
></TT
>_int_vector
);
NETDEVTAB_ENTRY(<TT
CLASS="REPLACEABLE"
><I
>DRV</I
></TT
>_netdev,
"<TT
CLASS="REPLACEABLE"
><I
>DRV</I
></TT
>",
<TT
CLASS="REPLACEABLE"
><I
>DRV_HRDWR</I
></TT
>_init,
&<TT
CLASS="REPLACEABLE"
><I
>DRV</I
></TT
>_sc);</PRE
></TD
></TR
></TABLE
></P
><P
>This, along with the referenced functions, completely define the driver.</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>If one needed the same low-level driver to handle
multiple similar hardware interfaces, you would need multiple invocations
of the
<TT
CLASS="FUNCTION"
>ETH_DRV_SC()</TT
>/<TT
CLASS="FUNCTION"
>NETDEVTAB_ENTRY()</TT
>
macros. You would add a pointer
to some instance specific data, e.g. containing base addresses, interrupt
numbers, etc, where the
<TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> 0, // No driver specific data</PRE
></TD
></TR
></TABLE
>
is currently.</P
></BLOCKQUOTE
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