source: rtems/doc/networking/driver.t @ 33fefc2

4.104.114.84.9
Last change on this file since 33fefc2 was 33fefc2, checked in by Joel Sherrill <joel.sherrill@…>, on Mar 23, 1999 at 11:17:52 PM

Patch from Eric Norum to account for new routine that improved
parsing of interface names.

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File size: 10.5 KB
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1@c
2@c  Written by Eric Norum
3@c
4@c  COPYRIGHT (c) 1988-1998.
5@c  On-Line Applications Research Corporation (OAR).
6@c  All rights reserved.
7@c
8@c  $Id$
9@c
10
11@chapter Networking Driver
12
13@section Introduction
14
15This chapter is intended to provide an introduction to the
16procedure for writing RTEMS network device drivers.
17The example code is taken from the `Generic 68360' network device
18driver.  The source code for this driver is located in the
19@code{c/src/lib/libbsp/m68k/gen68360/network} directory in the RTEMS
20source code distribution.  Having a copy of this driver at
21hand when reading the following notes will help significantly.
22
23@section Learn about the network device
24
25Before starting to write the network driver become completely
26familiar with the programmer's view of the device.
27The following points list some of the details of the
28device that must be understood before a driver can be written.
29
30@itemize @bullet
31
32@item Does the device use DMA to transfer packets to and from
33memory or does the processor have to
34copy packets to and from memory on the device?
35
36@item If the device uses DMA, is it capable of forming a single
37outgoing packet from multiple fragments scattered in separate
38memory buffers?
39
40@item If the device uses DMA, is it capable of chaining multiple
41outgoing packets, or does each outgoing packet require
42intervention by the driver?
43
44@item Does the device automatically pad short frames to the minimum
4564 bytes or does the driver have to supply the padding?
46
47@item Does the device automatically retry a transmission on detection
48of a collision?
49
50@item If the device uses DMA, is it capable of buffering multiple
51packets to memory, or does the receiver have to be restarted
52after the arrival of each packet?
53
54@item How are packets that are too short, too long, or received with
55CRC errors handled?  Does the device automatically continue
56reception or does the driver have to intervene?
57
58@item How is the device Ethernet address set?  How is the device
59programmed to accept or reject broadcast and multicast packets?
60
61@item What interrupts does the device generate?  Does it generate an
62interrupt for each incoming packet, or only for packets received
63without error?  Does it generate an interrupt for each packet
64transmitted, or only when the transmit queue is empty?  What
65happens when a transmit error is detected?
66
67@end itemize
68
69In addition, some controllers have specific questions regarding
70board specific configuration.  For example, the SONIC Ethernet
71controller has a very configurable data bus interface.  It can
72even be configured for sixteen and thirty-two bit data buses.  This
73type of information should be obtained from the board vendor.
74
75@section Understand the network scheduling conventions
76
77When writing code for the driver transmit and receive tasks,
78take care to follow the network scheduling conventions.  All tasks
79which are associated with networking share various
80data structures and resources.  To ensure the consistency
81of these structures the tasks
82execute only when they hold the network semaphore (@code{rtems_bsdnet_semaphore}).
83The transmit and receive tasks must abide by this protocol.  Be very
84careful to avoid `deadly embraces' with the other network tasks.
85A number of routines are provided to make it easier for the network
86driver code to conform to the network task scheduling conventions.
87
88@itemize @bullet
89
90@item @code{void rtems_bsdnet_semaphore_release(void)}
91
92This function releases the network semaphore.
93The network driver tasks must call this function immediately before
94making any blocking RTEMS request.
95
96@item @code{void rtems_bsdnet_semaphore_obtain(void)}
97
98This function obtains the network semaphore.
99If a network driver task has released the network semaphore to allow other
100network-related tasks to run while the task blocks, then this function must
101be called to reobtain the semaphore immediately after the return from the
102blocking RTEMS request.
103
104@item @code{rtems_bsdnet_event_receive(rtems_event_set, rtems_option, rtems_interval, rtems_event_set *)}
105The network driver task should call this function when it wishes to wait
106for an event.  This function releases the network semaphore,
107calls @code{rtems_event_receive} to wait for the specified event
108or events and reobtains the semaphore.
109The value returned is the value returned by the @code{rtems_event_receive}.
110
111@end itemize
112
113@section Write the Driver Attach Function
114The driver attach function is responsible for configuring the driver
115and making the connection between the network stack
116and the driver.
117
118Driver attach functions take a pointer to an
119@code{rtems_bsdnet_ifconfig} structure as their only argument.
120and set the driver parameters based on the
121values in this structure.  If an entry in the configuration
122structure is zero the attach function chooses an
123appropriate default value for that parameter.
124
125
126The driver should then set up several fields in the ifnet structure
127in the device-dependent data structure supplied and maintained by the driver:
128
129@table @code
130@item ifp->if_softc
131Pointer to the device-dependent data.  The first entry
132in the device-dependent data structure must be an @code{arpcom}
133structure.
134
135@item ifp->if_name
136The name of the device.  The network stack uses this string
137and the device number for device name lookups.  The device name should
138be obtained from the @code{name} entry in the configuration structure.
139
140@item ifp->if_unit
141The device number.  The network stack uses this number and the
142device name for device name lookups.  For example, if
143@code{ifp->if_name} is @samp{scc} and @code{ifp->if_unit} is @samp{1},
144the full device name would be @samp{scc1}.  The unit number should be
145obtained from the `name' entry in the configuration structure.
146
147@item ifp->if_mtu
148The maximum transmission unit for the device.  For Ethernet
149devices this value should almost always be 1500.
150
151@item ifp->if_flags
152The device flags.  Ethernet devices should set the flags
153to @code{IFF_BROADCAST|IFF_SIMPLEX}, indicating that the
154device can broadcast packets to multiple destinations
155and does not receive and transmit at the same time.
156
157@item ifp->if_snd.ifq_maxlen
158The maximum length of the queue of packets waiting to be
159sent to the driver.  This is normally set to @code{ifqmaxlen}.
160
161@item ifp->if_init
162The address of the driver initialization function.
163
164@item ifp->if_start
165The address of the driver start function.
166
167@item ifp->if_ioctl
168The address of the driver ioctl function.
169
170@item ifp->if_output
171The address of the output function.  Ethernet devices
172should set this to @code{ether_output}.
173@end table
174
175RTEMS provides a function to parse the driver name in the
176configuration structure into a device name and unit number.
177
178@example
179int rtems_bsdnet_parse_driver_name (
180  const struct rtems_bsdnet_ifconfig *config,
181  char **namep
182);
183@end example
184
185The function takes two arguments; a pointer to the configuration
186structure and a pointer to a pointer to a character.  The function
187parses the configuration name entry, allocates memory for the driver
188name, places the driver name in this memory, sets the second argument
189to point to the name and returns the unit number.
190On error, a message is printed and -1 is returned.
191
192Once the attach function  has set up the above entries it must link the
193driver data structure onto the list of devices by
194calling @code{if_attach}.  Ethernet devices should then
195call @code{ether_ifattach}.  Both functions take a pointer to the
196device's @code{ifnet} structure as their only argument.
197
198The attach function should return a non-zero value to indicate that
199the driver has been successfully configured and attached.
200
201@section Write the Driver Start Function.
202This function is called each time the network stack wants to start the
203transmitter.  This occures whenever the network stack adds a packet
204to a device's send queue and the @code{IFF_OACTIVE} bit in the
205device's @code{if_flags} is not set.
206
207For many devices this function need only set the @code{IFF_OACTIVE} bit in the
208@code{if_flags} and send an event to the transmit task
209indicating that a packet is in the driver transmit queue.
210
211
212@section Write the Driver Initialization Function.
213
214This function should initialize the device, attach to interrupt handler,
215and start the driver transmit and receive tasks.  The function
216
217@example
218rtems_id
219rtems_bsdnet_newproc (char *name,
220                      int stacksize,
221                      void(*entry)(void *),
222                      void *arg);
223@end example
224
225should be used to start the driver tasks.
226
227Note that the network stack may call the driver initialization function more
228than once.
229Make sure multiple versions of the receive and transmit tasks are not accidentally
230started.
231
232
233
234@section Write the Driver Transmit Task
235
236This task is reponsible for removing packets from the driver send queue and sending them to the device.  The task should block waiting for an event from the
237driver start function indicating that packets are waiting to be transmitted.
238When the transmit task has drained the driver send queue the task should clear
239the @code{IFF_OACTIVE} bit in @code{if_flags} and block until another outgoing
240packet is queued.
241
242
243@section Write the Driver Receive Task
244This task should block until a packet arrives from the device.  If the
245device is an Ethernet interface the function @code{ether_input} should be called
246to forward the packet to the network stack.   The arguments to @code{ether_input}
247are a pointer to the interface data structure, a pointer to the ethernet
248header and a pointer to an mbuf containing the packet itself.
249
250
251
252
253@section Write the Driver Interrupt Handler
254A typical interrupt handler will do nothing more than the hardware
255manipulation required to acknowledge the interrupt and send an RTEMS event
256to wake up the driver receive or transmit task waiting for the event.
257Network interface interrupt handlers must not make any calls to other
258network routines.
259
260
261
262@section Write the Driver IOCTL Function
263This function handles ioctl requests directed at the device.  The ioctl
264commands which must be handled are:
265
266@table @code
267@item SIOCGIFADDR
268@item SIOCSIFADDR
269If the device is an Ethernet interface these
270commands should be passed on to @code{ether_ioctl}.
271
272@item SIOCSIFFLAGS
273This command should be used to start or stop the device,
274depending on the state of the interface @code{IFF_UP} and
275@code{IFF_RUNNING} bits in @code{if_flags}:
276@table @code
277@item IFF_RUNNING
278Stop the device.
279
280@item IFF_UP
281Start the device.
282
283@item IFF_UP|IFF_RUNNING
284Stop then start the device.
285
286@item 0
287Do nothing.
288
289@end table
290@end table
291
292
293
294@section Write the Driver Statistic-Printing Function
295This function should print the values of any statistic/diagnostic
296counters the network driver may use.  The driver ioctl function should call
297the statistic-printing function when the ioctl command is
298@code{SIO_RTEMS_SHOW_STATS}.
299
300
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