linux: Initial support for running Klipper in a Linux real-time process

Add support for compiling the Klipper micro-controller code as a
real-time process capable of running on standard Linux systems.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/linux/main.c

@@ -0,0 +1,99 @@
+// Main starting point for micro-controller code running on linux systems
+//
+// Copyright (C) 2017  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include </usr/include/sched.h> // sched_setscheduler
+#include <stdio.h> // fprintf
+#include <string.h> // memset
+#include <unistd.h> // getopt
+#include "board/misc.h" // console_sendf
+#include "command.h" // DECL_CONSTANT
+#include "internal.h" // console_setup
+#include "sched.h" // sched_main
+
+DECL_CONSTANT(MCU, "linux");
+
+
+/****************************************************************
+ * Real-time setup
+ ****************************************************************/
+
+static int
+realtime_setup(void)
+{
+    struct sched_param sp;
+    memset(&sp, 0, sizeof(sp));
+    sp.sched_priority = 1;
+    int ret = sched_setscheduler(0, SCHED_FIFO, &sp);
+    if (ret < 0) {
+        report_errno("sched_setscheduler", ret);
+        return -1;
+    }
+    return 0;
+}
+
+
+/****************************************************************
+ * Restart
+ ****************************************************************/
+
+static char **orig_argv;
+
+void
+command_config_reset(uint32_t *args)
+{
+    if (! sched_is_shutdown())
+        shutdown("config_reset only available when shutdown");
+    int ret = execv(orig_argv[0], orig_argv);
+    report_errno("execv", ret);
+}
+DECL_COMMAND_FLAGS(config_reset, HF_IN_SHUTDOWN, "config_reset");
+
+
+/****************************************************************
+ * Startup
+ ****************************************************************/
+
+int
+main(int argc, char **argv)
+{
+    // Parse program args
+    orig_argv = argv;
+    int opt, watchdog = 0, realtime = 0;
+    while ((opt = getopt(argc, argv, "wr")) != -1) {
+        switch (opt) {
+        case 'w':
+            watchdog = 1;
+            break;
+        case 'r':
+            realtime = 1;
+            break;
+        default:
+            fprintf(stderr, "Usage: %s [-w] [-r]\n", argv[0]);
+            return -1;
+        }
+    }
+
+    // Initial setup
+    if (watchdog) {
+        int ret = watchdog_setup();
+        if (ret)
+            return ret;
+    }
+
+    if (realtime) {
+        int ret = realtime_setup();
+        if (ret)
+            return ret;
+    }
+
+    int ret = console_setup("/tmp/klipper_host_mcu");
+    if (ret)
+        return -1;
+
+    // Main loop
+    sched_main();
+    return 0;
+}