AP_HAL_Linux: add Led_Sysfs class.

Add a class to control leds via linux sysfs API.

libraries/AP_HAL_Linux/Led_Sysfs.cpp

@@ -0,0 +1,92 @@
+/*
+   Copyright (C) 2017 Mathieu Othacehe. All rights reserved.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "Led_Sysfs.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <inttypes.h>
+#include <unistd.h>
+
+#include <AP_HAL/AP_HAL.h>
+
+static const AP_HAL::HAL &hal = AP_HAL::get_HAL();
+
+namespace Linux {
+
+Led_Sysfs::Led_Sysfs(const char *led_name)
+    : _led_name(led_name)
+{
+}
+
+Led_Sysfs::~Led_Sysfs()
+{
+    if (_brightness_fd) {
+        close(_brightness_fd);
+    }
+}
+
+bool Led_Sysfs::init()
+{
+    char *br_path;
+    char *max_br_path;
+
+    if (asprintf(&br_path, "/sys/class/leds/%s/brightness", _led_name) == -1) {
+        AP_HAL::panic("LinuxLed_Sysfs : Couldn't allocate brightness path\n");
+    }
+
+    _brightness_fd = open(br_path, O_WRONLY | O_CLOEXEC);
+    if (_brightness_fd < 0) {
+        printf("LinuxLed_Sysfs: Unable to open file %s\n", br_path);
+        free(br_path);
+        return false;
+    }
+
+    if (asprintf(&max_br_path, "/sys/class/leds/%s/max_brightness", _led_name) == -1) {
+        AP_HAL::panic("LinuxLed_Sysfs : Couldn't allocate max_brightness path\n");
+    }
+
+    if (Util::from(hal.util)->read_file(max_br_path, "%u", &_max_brightness) < 0) {
+        AP_HAL::panic("LinuxLed_Sysfs : Unable to read max_brightness in %s\n",
+                      max_br_path);
+    }
+
+    free(max_br_path);
+    free(br_path);
+
+    return true;
+}
+
+bool Led_Sysfs::set_brightness(uint8_t brightness)
+{
+    if (_brightness_fd < 0) {
+        return false;
+    }
+
+    int br = brightness * _max_brightness / UINT8_MAX;
+
+    /* Don't log fails since this could spam the console */
+    if (dprintf(_brightness_fd, "%u", br) < 0) {
+        return false;
+    }
+
+    return true;
+}
+
+}

libraries/AP_HAL_Linux/Led_Sysfs.h

@@ -0,0 +1,41 @@
+/*
+  Copyright (C) 2017 Mathieu Othacehe. All rights reserved.
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program 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 General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <AP_HAL/AP_HAL.h>
+
+#include "AP_HAL_Linux.h"
+#include "Util.h"
+
+#pragma once
+
+namespace Linux {
+
+class Led_Sysfs {
+public:
+    bool init();
+    bool set_brightness(uint8_t brightness);
+
+    Led_Sysfs(const char* led_name);
+    ~Led_Sysfs();
+
+private:
+    int _brightness_fd = -1;
+    int _max_brightness = 0;
+    const char *_led_name = nullptr;
+};
+
+}