source: rtems/doc/networking/driver.t @ 5409453

4.104.114.84.9
Last change on this file since 5409453 was 5409453, checked in by Joel Sherrill <joel.sherrill@…>, on Apr 19, 1999 at 2:54:58 PM

First cut at addition of information on macros that need to be defined.

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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 Network Driver Makefile
114
115Network drivers are considered part of the BSD network package and as such
116are to be compiled with the appropriate flags.
117
118@example
119-D_COMPILING_BSD_KERNEL_ -DKERNEL -DINET -DNFS -DDIAGNOSTIC -DBOOTP_COMPAT
120@end example
121
122Defining these macros tells the network header files that the driver
123is to be compiled with extended visibility into the network stack.  This
124is in sharp contrast to applications that simply use the network stack.
125Applications do not require this level of visibility and should stick
126to the portable application level API.
127
128As a direct result of being logically internal to the network stack,
129network drivers use the BSD memory allocation routines   This means,
130for example, that malloc takes three arguments.  See the SONIC
131device driver (@code{c/src/lib/libchip/network/sonic.c}) for an example
132of this.  Because of this, network drivers should not include
133@code{<stdlib.h>}.  Doing so will result in conflicting definitions
134of @code{malloc()}.
135
136@b{Application level} code including network servers such as the FTP
137daemon are @b{not} part of the BSD network package and should not be
138compiled with the BSD network flags.  They should include
139@code{<stdlib.h>} and not define the network stack visibility
140macros.
141
142@section Write the Driver Attach Function
143The driver attach function is responsible for configuring the driver
144and making the connection between the network stack
145and the driver.
146
147Driver attach functions take a pointer to an
148@code{rtems_bsdnet_ifconfig} structure as their only argument.
149and set the driver parameters based on the
150values in this structure.  If an entry in the configuration
151structure is zero the attach function chooses an
152appropriate default value for that parameter.
153
154
155The driver should then set up several fields in the ifnet structure
156in the device-dependent data structure supplied and maintained by the driver:
157
158@table @code
159@item ifp->if_softc
160Pointer to the device-dependent data.  The first entry
161in the device-dependent data structure must be an @code{arpcom}
162structure.
163
164@item ifp->if_name
165The name of the device.  The network stack uses this string
166and the device number for device name lookups.  The device name should
167be obtained from the @code{name} entry in the configuration structure.
168
169@item ifp->if_unit
170The device number.  The network stack uses this number and the
171device name for device name lookups.  For example, if
172@code{ifp->if_name} is @samp{scc} and @code{ifp->if_unit} is @samp{1},
173the full device name would be @samp{scc1}.  The unit number should be
174obtained from the `name' entry in the configuration structure.
175
176@item ifp->if_mtu
177The maximum transmission unit for the device.  For Ethernet
178devices this value should almost always be 1500.
179
180@item ifp->if_flags
181The device flags.  Ethernet devices should set the flags
182to @code{IFF_BROADCAST|IFF_SIMPLEX}, indicating that the
183device can broadcast packets to multiple destinations
184and does not receive and transmit at the same time.
185
186@item ifp->if_snd.ifq_maxlen
187The maximum length of the queue of packets waiting to be
188sent to the driver.  This is normally set to @code{ifqmaxlen}.
189
190@item ifp->if_init
191The address of the driver initialization function.
192
193@item ifp->if_start
194The address of the driver start function.
195
196@item ifp->if_ioctl
197The address of the driver ioctl function.
198
199@item ifp->if_output
200The address of the output function.  Ethernet devices
201should set this to @code{ether_output}.
202@end table
203
204RTEMS provides a function to parse the driver name in the
205configuration structure into a device name and unit number.
206
207@example
208int rtems_bsdnet_parse_driver_name (
209  const struct rtems_bsdnet_ifconfig *config,
210  char **namep
211);
212@end example
213
214The function takes two arguments; a pointer to the configuration
215structure and a pointer to a pointer to a character.  The function
216parses the configuration name entry, allocates memory for the driver
217name, places the driver name in this memory, sets the second argument
218to point to the name and returns the unit number.
219On error, a message is printed and -1 is returned.
220
221Once the attach function  has set up the above entries it must link the
222driver data structure onto the list of devices by
223calling @code{if_attach}.  Ethernet devices should then
224call @code{ether_ifattach}.  Both functions take a pointer to the
225device's @code{ifnet} structure as their only argument.
226
227The attach function should return a non-zero value to indicate that
228the driver has been successfully configured and attached.
229
230@section Write the Driver Start Function.
231This function is called each time the network stack wants to start the
232transmitter.  This occures whenever the network stack adds a packet
233to a device's send queue and the @code{IFF_OACTIVE} bit in the
234device's @code{if_flags} is not set.
235
236For many devices this function need only set the @code{IFF_OACTIVE} bit in the
237@code{if_flags} and send an event to the transmit task
238indicating that a packet is in the driver transmit queue.
239
240
241@section Write the Driver Initialization Function.
242
243This function should initialize the device, attach to interrupt handler,
244and start the driver transmit and receive tasks.  The function
245
246@example
247rtems_id
248rtems_bsdnet_newproc (char *name,
249                      int stacksize,
250                      void(*entry)(void *),
251                      void *arg);
252@end example
253
254should be used to start the driver tasks.
255
256Note that the network stack may call the driver initialization function more
257than once.
258Make sure multiple versions of the receive and transmit tasks are not accidentally
259started.
260
261
262
263@section Write the Driver Transmit Task
264
265This 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
266driver start function indicating that packets are waiting to be transmitted.
267When the transmit task has drained the driver send queue the task should clear
268the @code{IFF_OACTIVE} bit in @code{if_flags} and block until another outgoing
269packet is queued.
270
271
272@section Write the Driver Receive Task
273This task should block until a packet arrives from the device.  If the
274device is an Ethernet interface the function @code{ether_input} should be called
275to forward the packet to the network stack.   The arguments to @code{ether_input}
276are a pointer to the interface data structure, a pointer to the ethernet
277header and a pointer to an mbuf containing the packet itself.
278
279
280
281
282@section Write the Driver Interrupt Handler
283A typical interrupt handler will do nothing more than the hardware
284manipulation required to acknowledge the interrupt and send an RTEMS event
285to wake up the driver receive or transmit task waiting for the event.
286Network interface interrupt handlers must not make any calls to other
287network routines.
288
289
290
291@section Write the Driver IOCTL Function
292This function handles ioctl requests directed at the device.  The ioctl
293commands which must be handled are:
294
295@table @code
296@item SIOCGIFADDR
297@item SIOCSIFADDR
298If the device is an Ethernet interface these
299commands should be passed on to @code{ether_ioctl}.
300
301@item SIOCSIFFLAGS
302This command should be used to start or stop the device,
303depending on the state of the interface @code{IFF_UP} and
304@code{IFF_RUNNING} bits in @code{if_flags}:
305@table @code
306@item IFF_RUNNING
307Stop the device.
308
309@item IFF_UP
310Start the device.
311
312@item IFF_UP|IFF_RUNNING
313Stop then start the device.
314
315@item 0
316Do nothing.
317
318@end table
319@end table
320
321
322
323@section Write the Driver Statistic-Printing Function
324This function should print the values of any statistic/diagnostic
325counters the network driver may use.  The driver ioctl function should call
326the statistic-printing function when the ioctl command is
327@code{SIO_RTEMS_SHOW_STATS}.
328
329
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