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authorJoel Sherrill <joel.sherrill@OARcorp.com>1999-03-02 15:56:04 +0000
committerJoel Sherrill <joel.sherrill@OARcorp.com>1999-03-02 15:56:04 +0000
commit97b8b8f5fa568d2cdb96a39d0e7acd63d38cedd2 (patch)
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-@c
-@c Written by Eric Norum
-@c
-@c COPYRIGHT (c) 1988-1998.
-@c On-Line Applications Research Corporation (OAR).
-@c All rights reserved.
-@c
-@c $Id$
-@c
-
-@chapter Networking Driver
-
-@section Introduction
-
-This chapter is intended to provide an introduction to the
-procedure for writing RTEMS network device drivers.
-The example code is taken from the `Generic 68360' network device
-driver. The source code for this driver is located in the
-@code{c/src/lib/libbsp/m68k/gen68360/network} directory in the RTEMS
-source code distribution. You should have a copy of this driver at
-hand when reading the following notes.
-
-@section Learn about the network device
-
-Before starting to write the network driver you need to be completely
-familiar with the programmer's view of the device.
-The following points list some of the details of the
-device that must be understood before a driver can be written.
-
-@itemize @bullet
-
-@item Does the device use DMA to transfer packets to and from
-memory or does the processor have to
-copy packets to and from memory on the device?
-
-@item If the device uses DMA, is it capable of forming a single
-outtoing packet from multiple fragments scattered in separate
-memory buffers?
-
-@item If the device uses DMA, is it capable of chaining multiple
-outgoing packets, or does each outgoing packet require
-intervention by the driver?
-
-@item Does the device automatically pad short frames to the minimum
-64 bytes or does the driver have to supply the padding?
-
-@item Does the device automatically retry a transmission on detection
-of a collision?
-
-@item If the device uses DMA, is it capable of buffering multiple
-packets to memory, or does the receiver have to be restarted
-after the arrival of each packet?
-
-@item How are packets that are too short, too long, or received with
-CRC errors handled? Does the device automatically continue
-reception or does the driver have to intervene?
-
-@item How is the device Ethernet address set? How is the device
-programmed to accept or reject broadcast and multicast packets?
-
-@item What interrupts does the device generate? Does it generate an
-interrupt for each incoming packet, or only for packets received
-without error? Does it generate an interrupt for each packet
-transmitted, or only when the transmit queue is empty? What
-happens when a transmit error is detected?
-
-@end itemize
-
-In addition, some controllers have specific questions regarding
-board specific configuration. For example, the SONIC Ethernet
-controller has a very configurable data bus interface. It can
-even be configured for sixteen and thirty-two bit data buses. This
-type of information should be obtained from the board vendor.
-
-@section Understand the network scheduling conventions
-
-When writing code for your driver transmit and receive tasks you must
-take care to follow the network scheduling conventions. All tasks
-which are associated with networking share various
-data structures and resources. To ensure the consistency
-of these structures the tasks
-execute only when they hold the network semaphore (@code{rtems_bsdnet_semaphore}).
-Your transmit and receive tasks must abide by this protocol which means you must
-be careful to avoid `deadly embraces' with the other network tasks.
-A number of routines are provided to make it easier for your code
-to conform to the network task scheduling conventions.
-
-@itemize @bullet
-
-@item @code{void rtems_bsdnet_semaphore_release(void)}
-
-This function releases the network semaphore.
-Your task must call this function immediately before
-making any blocking RTEMS request.
-
-@item @code{void rtems_bsdnet_semaphore_obtain(void)}
-
-This function obtains the network semaphore.
-If your task has released the network semaphore to allow other
-network-related tasks to run while your task blocks you must call this
-function to reobtain the semaphore immediately after the return from the
-blocking RTEMS request.
-
-@item @code{rtems_bsdnet_event_receive(rtems_event_set, rtems_option, rtems_interval, rtems_event_set *)}
-Your task should call this function when it wishes to wait for an event.
-This function releases the network semaphore,
-calls @code{rtems_event_receive} to wait for the specified event
-or events and reobtains the semaphore.
-The value returned is the value returned by the @code{rtems_event_receive}.
-
-@end itemize
-
-@section Write your driver attach function
-The driver attach function is responsible for configuring the driver
-and making the connection between the network stack
-and the driver.
-
-Driver attach functions take a pointer to an
-@code{rtems_bsdnet_ifconfig} structure as their only argument.
-and set the driver parameters based on the
-values in this structure. If an entry in the configuration
-structure is zero the attach function chooses an
-appropriate default value for that parameter.
-
-
-The driver should then set up several fields in the ifnet structure
-in the device-dependent data structure supplied and maintained by the driver:
-
-@table @code
-@item ifp->if_softc
-Pointer to the device-dependent data. The first entry
-in the device-dependent data structure must be an @code{arpcom}
-structure.
-
-@item ifp->if_name
-The name of the device. The network stack uses this string
-and the device number for device name lookups. The name should not
-contain digits as these will be assumed to be part of the unit number
-and not part of the device name.
-
-
-@item ifp->if_unit
-The device number. The network stack uses this number and the
-device name for device name lookups. For example, if
-@code{ifp->if_name} is @samp{scc}, and @code{ifp->if_unit} is @samp{1},
-the full device name would be @samp{scc1}.
-
-@item ifp->if_mtu
-The maximum transmission unit for the device. For Ethernet
-devices this value should almost always be 1500.
-
-@item ifp->if_flags
-The device flags. Ethernet devices should set the flags
-to @code{IFF_BROADCAST|IFF_SIMPLEX}, indicating that the
-device can broadcast packets to multiple destinations
-and does not receive and transmit at the same time.
-
-@item ifp->if_snd.ifq_maxlen
-The maximum length of the queue of packets waiting to be
-sent to the driver. This is normally set to @code{ifqmaxlen}.
-
-@item ifp->if_init
-The address of the driver initialization function.
-
-@item ifp->if_start
-The address of the driver start function.
-
-@item ifp->if_ioctl
-The address of the driver ioctl function.
-
-@item ifp->if_output
-The address of the output function. Ethernet devices
-should set this to @code{ether_output}.
-@end table
-
-Once the attach function has set up the above entries it must link the
-driver data structure onto the list of devices by
-calling @code{if_attach}. Ethernet devices should then
-call @code{ether_ifattach}. Both functions take a pointer to the
-device's @code{ifnet} structure as their only argument.
-
-The attach function should return a non-zero value to indicate that
-the driver has been successfully configured and attached.
-
-
-
-
-@section Write your driver start function.
-This function is called each time the network stack wants to start the
-transmitter. This occures whenever the network stack adds a packet
-to a device's send queue and the @code{IFF_OACTIVE} bit in the
-device's @code{if_flags} is not set.
-
-For many devices this function need only set the @code{IFF_OACTIVE} bit in the
-@code{if_flags} and send an event to the transmit task
-indicating that a packet is in the driver transmit queue.
-
-
-@section Write your driver initialization function.
-This function should initialize the device, attach to interrupt handler,
-and start the driver transmit and receive tasks. The function
-
-@example
-rtems_id
-rtems_bsdnet_newproc (char *name,
- int stacksize,
- void(*entry)(void *),
- void *arg);
-@end example
-
-should be used to start the driver tasks.
-
-Note that the network stack may call the driver initialization function more
-than once.
-Make sure you don't start multiple versions of the receive and transmit tasks.
-
-
-
-@section Write your driver transmit task.
-This 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
-driver start function indicating that packets are waiting to be transmitted.
-When the transmit task has drained the driver send queue the task should clear
-the @code{IFF_OACTIVE} bit in @code{if_flags} and block until another outgoing
-packet is queued.
-
-
-@section Write your driver receive task.
-This task should block until a packet arrives from the device. If the
-device is an Ethernet interface the function @code{ether_input} should be called
-to forward the packet to the network stack. The arguments to @code{ether_input}
-are a pointer to the interface data structure, a pointer to the ethernet
-header and a pointer to an mbuf containing the packet itself.
-
-
-
-
-@section Write your driver interrupt handler.
-A typical interrupt handler will do nothing more than the hardware
-manipulation required to acknowledge the interrupt and send an RTEMS event
-to wake up the driver receive or transmit task waiting for the event.
-Network interface interrupt handlers must not make any calls to other
-network routines.
-
-
-
-@section Write your driver ioctl function.
-This function handles ioctl requests directed at the device. The ioctl
-commands which must be handled are:
-
-@table @code
-@item SIOCGIFADDR
-@item SIOCSIFADDR
-If the device is an Ethernet interface these
-commands should be passed on to @code{ether_ioctl}.
-
-@item SIOCSIFFLAGS
-This command should be used to start or stop the device,
-depending on the state of the interface @code{IFF_UP} and
-@code{IFF_RUNNING} bits in @code{if_flags}:
-@table @code
-@item IFF_RUNNING
-Stop the device.
-
-@item IFF_UP
-Start the device.
-
-@item IFF_UP|IFF_RUNNING
-Stop then start the device.
-
-@item 0
-Do nothing.
-
-@end table
-@end table
-
-
-
-@section Write Your Driver Statistic-Printing Function
-This function should print the values of any statistic/diagnostic
-counters your driver may use. The driver ioctl function should call
-the statistic-printing function when the ioctl command is
-@code{SIO_RTEMS_SHOW_STATS}.
-
-