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diff --git a/legacy-networking/networking_driver.rst b/legacy-networking/networking_driver.rst new file mode 100644 index 0000000..c161c2b --- /dev/null +++ b/legacy-networking/networking_driver.rst @@ -0,0 +1,305 @@ +.. SPDX-License-Identifier: CC-BY-SA-4.0 + +.. COMMENT: Written by Eric Norum +.. Copyright (C) 1988, 2002 On-Line Applications Research Corporation (OAR) + +Networking Driver +################# + +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 :file:`bsps/m68k/gen68360/net` directory in the +RTEMS source code distribution. Having a copy of this driver at hand when +reading the following notes will help significantly. + +Learn about the network device +============================== + +Before starting to write the network driver become 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. + +- 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? + +- If the device uses DMA, is it capable of forming a single outgoing packet + from multiple fragments scattered in separate memory buffers? + +- If the device uses DMA, is it capable of chaining multiple outgoing packets, + or does each outgoing packet require intervention by the driver? + +- Does the device automatically pad short frames to the minimum 64 bytes or + does the driver have to supply the padding? + +- Does the device automatically retry a transmission on detection of a + collision? + +- 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? + +- 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? + +- How is the device Ethernet address set? How is the device programmed to + accept or reject broadcast and multicast packets? + +- 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? + +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. + +Understand the network scheduling conventions +============================================= + +When writing code for the driver transmit and receive tasks, 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 (``rtems_bsdnet_semaphore``). The transmit and receive tasks +must abide by this protocol. Be very careful to avoid 'deadly embraces' with +the other network tasks. A number of routines are provided to make it easier +for the network driver code to conform to the network task scheduling +conventions. + +- ``void rtems_bsdnet_semaphore_release(void)`` + This function releases the network semaphore. The network driver tasks must + call this function immediately before making any blocking RTEMS request. + +- ``void rtems_bsdnet_semaphore_obtain(void)`` + This function obtains the network semaphore. If a network driver task has + released the network semaphore to allow other network-related tasks to run + while the task blocks, then this function must be called to reobtain the + semaphore immediately after the return from the blocking RTEMS request. + +- ``rtems_bsdnet_event_receive(rtems_event_set, rtems_option, rtems_interval, rtems_event_set *)`` + The network driver task should call this function when it wishes to wait for + an event. This function releases the network semaphore, calls + ``rtems_event_receive`` to wait for the specified event or events and + reobtains the semaphore. The value returned is the value returned by the + ``rtems_event_receive``. + +Network Driver Makefile +======================= + +Network drivers are considered part of the BSD network package and as such are +to be compiled with the appropriate flags. This can be accomplished by adding +``-D__INSIDE_RTEMS_BSD_TCPIP_STACK__`` to the ``command line``. If the driver +is inside the RTEMS source tree or is built using the RTEMS application +Makefiles, then adding the following line accomplishes this: + +.. code-block:: makefile + + DEFINES += -D__INSIDE_RTEMS_BSD_TCPIP_STACK__ + +This is equivalent to the following list of definitions. Early versions of the +RTEMS BSD network stack required that all of these be defined. + +.. code-block:: makefile + + -D_COMPILING_BSD_KERNEL_ -DKERNEL -DINET -DNFS \ + -DDIAGNOSTIC -DBOOTP_COMPAT + +Defining these macros tells the network header files that the driver is to be +compiled with extended visibility into the network stack. This is in sharp +contrast to applications that simply use the network stack. Applications do +not require this level of visibility and should stick to the portable +application level API. + +As a direct result of being logically internal to the network stack, network +drivers use the BSD memory allocation routines This means, for example, that +malloc takes three arguments. See the SONIC device driver +(:file:`c/src/lib/libchip/network/sonic.c`) for an example of this. Because of +this, network drivers should not include ``<stdlib.h>``. Doing so will result +in conflicting definitions of ``malloc()``. + +*Application level* code including network servers such as the FTP daemon are +*not* part of the BSD kernel network code and should not be compiled with the +BSD network flags. They should include ``<stdlib.h>`` and not define the +network stack visibility macros. + +Write the 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 ``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: + +``ifp->if_softc`` + Pointer to the device-dependent data. The first entry in the + device-dependent data structure must be an ``arpcom`` structure. + +``ifp->if_name`` + The name of the device. The network stack uses this string and the device + number for device name lookups. The device name should be obtained from + the ``name`` entry in the configuration structure. + +``ifp->if_unit`` + The device number. The network stack uses this number and the device name + for device name lookups. For example, if ``ifp->if_name`` is ``scc`` and + ``ifp->if_unit`` is ``1``, the full device name would be ``scc1``. The + unit number should be obtained from the 'name' entry in the configuration + structure. + +``ifp->if_mtu`` + The maximum transmission unit for the device. For Ethernet devices this + value should almost always be 1500. + +``ifp->if_flags`` + The device flags. Ethernet devices should set the flags to + ``IFF_BROADCAST|IFF_SIMPLEX``, indicating that the device can broadcast + packets to multiple destinations and does not receive and transmit at the + same time. + +``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 ``ifqmaxlen``. + +``ifp->if_init`` + The address of the driver initialization function. + +``ifp->if_start`` + The address of the driver start function. + +``ifp->if_ioctl`` + The address of the driver ioctl function. + +``ifp->if_output`` + The address of the output function. Ethernet devices should set this to + ``ether_output``. + +RTEMS provides a function to parse the driver name in the configuration +structure into a device name and unit number. + +.. code-block:: c + + int rtems_bsdnet_parse_driver_name ( + const struct rtems_bsdnet_ifconfig *config, + char **namep + ); + +The function takes two arguments; a pointer to the configuration structure and +a pointer to a pointer to a character. The function parses the configuration +name entry, allocates memory for the driver name, places the driver name in +this memory, sets the second argument to point to the name and returns the unit +number. On error, a message is printed and ``-1`` is returned. + +Once the attach function has set up the above entries it must link the driver +data structure onto the list of devices by calling ``if_attach``. Ethernet +devices should then call ``ether_ifattach``. Both functions take a pointer to +the device's ``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. + +Write the 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 ``IFF_OACTIVE`` bit in the device's ``if_flags`` is +not set. + +For many devices this function need only set the ``IFF_OACTIVE`` bit in the +``if_flags`` and send an event to the transmit task indicating that a packet is +in the driver transmit queue. + +Write the Driver Initialization Function. +========================================= + +This function should initialize the device, attach to interrupt handler, and +start the driver transmit and receive tasks. The function + +.. code-block:: c + + rtems_id + rtems_bsdnet_newproc (char *name, + int stacksize, + void(*entry)(void *), + void *arg); + +should be used to start the driver tasks. + +Note that the network stack may call the driver initialization function more +than once. Make sure multiple versions of the receive and transmit tasks are +not accidentally started. + +Write the 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 ``IFF_OACTIVE`` bit in ``if_flags`` and block until another +outgoing packet is queued. + +Write the Driver Receive Task +============================= + +This task should block until a packet arrives from the device. If the device +is an Ethernet interface the function ``ether_input`` should be called to +forward the packet to the network stack. The arguments to ``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. + +Write the 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. + +Write the Driver IOCTL Function +=============================== + +This function handles ioctl requests directed at the device. The ioctl +commands which must be handled are: + +``SIOCGIFADDR`` + +``SIOCSIFADDR`` + If the device is an Ethernet interface these commands should be passed on + to ``ether_ioctl``. + +``SIOCSIFFLAGS`` + This command should be used to start or stop the device, depending on the + state of the interface ``IFF_UP`` and ``IFF_RUNNING`` bits in ``if_flags``: + + ``IFF_RUNNING`` + Stop the device. + + ``IFF_UP`` + Start the device. + + ``IFF_UP|IFF_RUNNING`` + Stop then start the device. + + ``0`` + Do nothing. + +Write the Driver Statistic-Printing Function +============================================ + +This function should print the values of any statistic/diagnostic counters the +network driver may use. The driver ioctl function should call the +statistic-printing function when the ioctl command is ``SIO_RTEMS_SHOW_STATS``. |