xddp-echo.c

/*
 * Copyright (C) 2009 Philippe Gerum <rpm@xenomai.org>.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.

 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA.
 *
 *
 * XDDP-based RT/NRT threads communication demo.
 *
 * Real-time Xenomai threads and regular Linux threads may want to
 * exchange data in a way that does not require the former to leave
 * the real-time domain (i.e. secondary mode). Message pipes - as
 * implemented by the RTDM-based XDDP protocol - are provided for this
 * purpose.
 *
 * On the Linux domain side, pseudo-device files named /dev/rtp<minor>
 * give regular POSIX threads access to non real-time communication
 * endpoints, via the standard character-based I/O interface. On the
 * Xenomai domain side, sockets may be bound to XDDP ports, which act
 * as proxies to send and receive data to/from the associated
 * pseudo-device files. Ports and pseudo-device minor numbers are
 * paired, meaning that e.g. port 7 will proxy the traffic for
 * /dev/rtp7. Therefore, port numbers may range from 0 to
 * CONFIG_XENO_OPT_PIPE_NRDEV - 1.
 *
 * All data sent through a bound/connected XDDP socket via sendto(2) or
 * write(2) will be passed to the peer endpoint in the Linux domain,
 * and made available for reading via the standard read(2) system
 * call. Conversely, all data sent using write(2) through the non
 * real-time endpoint will be conveyed to the real-time socket
 * endpoint, and made available to the recvfrom(2) or read(2) system
 * calls.
 *
 * Both threads can use the bi-directional data path to send and
 * receive datagrams in a FIFO manner, as illustrated by the simple
 * echoing process implemented by this program.
 *
 * realtime_thread------------------------------>-------+
 *   =>  get socket                                     |
 *   =>  bind socket to port 0                          v
 *   =>  write traffic to NRT domain via sendto()       |
 *   =>  read traffic from NRT domain via recvfrom() <--|--+
 *                                                      |  |
 * regular_thread---------------------------------------+  |
 *   =>  open /dev/rtp0                                 |  ^
 *   =>  read traffic from RT domain via read()         |  |
 *   =>  echo traffic back to RT domain via write()     +--+
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <malloc.h>
#include <pthread.h>
#include <fcntl.h>
#include <errno.h>
#include <rtdm/ipc.h>

pthread_t rt, nrt;

#define XDDP_PORT 0     /* [0..CONFIG-XENO_OPT_PIPE_NRDEV - 1] */

static const char *msg[] = {
        "Surfing With The Alien",
        "Lords of Karma",
        "Banana Mango",
        "Psycho Monkey",
        "Luminous Flesh Giants",
        "Moroccan Sunset",
        "Satch Boogie",
        "Flying In A Blue Dream",
        "Ride",
        "Summer Song",
        "Speed Of Light",
        "Crystal Planet",
        "Raspberry Jam Delta-V",
        "Champagne?",
        "Clouds Race Across The Sky",
        "Engines Of Creation"
};

static void fail(const char *reason)
{
        perror(reason);
        exit(EXIT_FAILURE);
}

static void *realtime_thread(void *arg)
{
        struct sockaddr_ipc saddr;
        int ret, s, n = 0, len;
        struct timespec ts;
        size_t poolsz;
        char buf[128];

        /*
         * Get a datagram socket to bind to the RT endpoint. Each
         * endpoint is represented by a port number within the XDDP
         * protocol namespace.
         */
        s = socket(AF_RTIPC, SOCK_DGRAM, IPCPROTO_XDDP);
        if (s < 0) {
                perror("socket");
                exit(EXIT_FAILURE);
        }

        /*
         * Set a local 16k pool for the RT endpoint. Memory needed to
         * convey datagrams will be pulled from this pool, instead of
         * Xenomai's system pool.
         */
        poolsz = 16384; /* bytes */
        ret = setsockopt(s, SOL_XDDP, XDDP_POOLSZ,
                         &poolsz, sizeof(poolsz));
        if (ret)
                fail("setsockopt");

        /*
         * Bind the socket to the port, to setup a proxy to channel
         * traffic to/from the Linux domain.
         *
         * saddr.sipc_port specifies the port number to use.
         */
        memset(&saddr, 0, sizeof(saddr));
        saddr.sipc_family = AF_RTIPC;
        saddr.sipc_port = XDDP_PORT;
        ret = bind(s, (struct sockaddr *)&saddr, sizeof(saddr));
        if (ret)
                fail("bind");

        for (;;) {
                len = strlen(msg[n]);
                /*
                 * Send a datagram to the NRT endpoint via the proxy.
                 * We may pass a NULL destination address, since a
                 * bound socket is assigned a default destination
                 * address matching the binding address (unless
                 * connect(2) was issued before bind(2), in which case
                 * the former would prevail).
                 */
                ret = sendto(s, msg[n], len, 0, NULL, 0);
                if (ret != len)
                        fail("sendto");

                printf("%s: sent %d bytes, \"%.*s\"\n",
                       __FUNCTION__, ret, ret, msg[n]);

                /* Read back packets echoed by the regular thread */
                ret = recvfrom(s, buf, sizeof(buf), 0, NULL, 0);
                if (ret <= 0)
                        fail("recvfrom");

                printf("   => \"%.*s\" echoed by peer\n", ret, buf);

                n = (n + 1) % (sizeof(msg) / sizeof(msg[0]));
                /*
                 * We run in full real-time mode (i.e. primary mode),
                 * so we have to let the system breathe between two
                 * iterations.
                 */
                ts.tv_sec = 0;
                ts.tv_nsec = 500000000; /* 500 ms */
                clock_nanosleep(CLOCK_REALTIME, 0, &ts, NULL);
        }

        return NULL;
}

static void *regular_thread(void *arg)
{
        char buf[128], *devname;
        int fd, ret;

        if (asprintf(&devname, "/dev/rtp%d", XDDP_PORT) < 0)
                fail("asprintf");

        fd = open(devname, O_RDWR);
        free(devname);
        if (fd < 0)
                fail("open");

        for (;;) {
                /* Get the next message from realtime_thread. */
                ret = read(fd, buf, sizeof(buf));
                if (ret <= 0)
                        fail("read");

                /* Echo the message back to realtime_thread. */
                ret = write(fd, buf, ret);
                if (ret <= 0)
                        fail("write");
        }

        return NULL;
}

int main(int argc, char **argv)
{
        struct sched_param rtparam = { .sched_priority = 42 };
        pthread_attr_t rtattr, regattr;
        sigset_t set;
        int sig;

        sigemptyset(&set);
        sigaddset(&set, SIGINT);
        sigaddset(&set, SIGTERM);
        sigaddset(&set, SIGHUP);
        pthread_sigmask(SIG_BLOCK, &set, NULL);

        pthread_attr_init(&rtattr);
        pthread_attr_setdetachstate(&rtattr, PTHREAD_CREATE_JOINABLE);
        pthread_attr_setinheritsched(&rtattr, PTHREAD_EXPLICIT_SCHED);
        pthread_attr_setschedpolicy(&rtattr, SCHED_FIFO);
        pthread_attr_setschedparam(&rtattr, &rtparam);

        errno = pthread_create(&rt, &rtattr, &realtime_thread, NULL);
        if (errno)
                fail("pthread_create");

        pthread_attr_init(&regattr);
        pthread_attr_setdetachstate(&regattr, PTHREAD_CREATE_JOINABLE);
        pthread_attr_setinheritsched(&regattr, PTHREAD_EXPLICIT_SCHED);
        pthread_attr_setschedpolicy(&regattr, SCHED_OTHER);

        errno = pthread_create(&nrt, &regattr, &regular_thread, NULL);
        if (errno)
                fail("pthread_create");

        sigwait(&set, &sig);
        pthread_cancel(rt);
        pthread_cancel(nrt);
        pthread_join(rt, NULL);
        pthread_join(nrt, NULL);

        return 0;
}