mirror of
https://codeberg.org/Freeyourgadget/Gadgetbridge
synced 2024-06-02 19:36:14 +02:00
4363f94661
This commit takes aims to bring many new garmin devices up to a working status, with basic functionalities such as: - garmin protocol initialization - basic message exchange - support for some messages in Garmin own format - support for some messages in protobuf format
48 lines
1.9 KiB
Java
48 lines
1.9 KiB
Java
/* Copyright (C) 2023-2024 Petr Kadlec
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This file is part of Gadgetbridge.
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Gadgetbridge is free software: you can redistribute it and/or modify
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it under the terms of the GNU Affero General Public License as published
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by the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Gadgetbridge is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Affero General Public License for more details.
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You should have received a copy of the GNU Affero General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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package nodomain.freeyourgadget.gadgetbridge.service.devices.garmin.messages;
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import java.nio.ByteBuffer;
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public final class ChecksumCalculator {
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private static final int[] CONSTANTS = {0x0000, 0xCC01, 0xD801, 0x1400, 0xF001, 0x3C00, 0x2800, 0xE401, 0xA001, 0x6C00, 0x7800, 0xB401, 0x5000, 0x9C01, 0x8801, 0x4400};
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private ChecksumCalculator() {
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}
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public static int computeCrc(byte[] data, int offset, int length) {
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return computeCrc(0, data, offset, length);
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}
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public static int computeCrc(ByteBuffer byteBuffer, int offset, int length) {
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byteBuffer.rewind();
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byte[] data = new byte[length];
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byteBuffer.get(data);
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return computeCrc(0, data, offset, length);
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}
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public static int computeCrc(int initialCrc, byte[] data, int offset, int length) {
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int crc = initialCrc;
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for (int i = offset; i < offset + length; ++i) {
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int b = data[i];
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crc = (((crc >> 4) & 4095) ^ CONSTANTS[crc & 15]) ^ CONSTANTS[b & 15];
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crc = (((crc >> 4) & 4095) ^ CONSTANTS[crc & 15]) ^ CONSTANTS[(b >> 4) & 15];
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}
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return crc;
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}
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}
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