1 /*
2 * Copyright (C) 2020 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include <libprotocan/Signal.h>
18
19 #include <android-base/logging.h>
20
21 namespace android::hardware::automotive::protocan {
22
calculateLastByteMask(uint16_t start,uint8_t length)23 static uint8_t calculateLastByteMask(uint16_t start, uint8_t length) {
24 unsigned lastByteBits = (start + length) % 8;
25 unsigned lastBytePadding = (8 - lastByteBits) % 8;
26 return 0xFF >> lastBytePadding;
27 }
28
calculateFirstByteMask(uint16_t firstByte,uint8_t firstBit,uint16_t lastByte,uint8_t lastMask)29 static uint8_t calculateFirstByteMask(uint16_t firstByte, uint8_t firstBit, uint16_t lastByte,
30 uint8_t lastMask) {
31 uint8_t firstMask = 0xFF << firstBit;
32 if (firstByte == lastByte) firstMask &= lastMask;
33 return firstMask;
34 }
35
Signal(uint16_t start,uint8_t length,value defVal)36 Signal::Signal(uint16_t start, uint8_t length, value defVal)
37 : maxValue((1u << length) - 1),
38 kFirstByte(start / 8),
39 kFirstBit(start % 8),
40 kFirstByteBits(8 - kFirstBit),
41 kLastByte((start + length - 1) / 8),
42 kLastMask(calculateLastByteMask(start, length)),
43 kFirstMask(calculateFirstByteMask(kFirstByte, kFirstBit, kLastByte, kLastMask)),
44 kDefVal(defVal) {
45 CHECK(length > 0) << "Signal length must not be zero";
46 }
47
get(const can::V1_0::CanMessage & msg) const48 Signal::value Signal::get(const can::V1_0::CanMessage& msg) const {
49 CHECK(msg.payload.size() > kLastByte)
50 << "Message is too short. Did you call MessageDef::validate?";
51
52 Signal::value v = 0;
53 if (kLastByte != kFirstByte) v = kLastMask & msg.payload[kLastByte];
54
55 for (int i = kLastByte - 1; i > kFirstByte; i--) {
56 v = (v << 8) | msg.payload[i];
57 }
58
59 return (v << kFirstByteBits) | ((msg.payload[kFirstByte] & kFirstMask) >> kFirstBit);
60 }
61
set(can::V1_0::CanMessage & msg,Signal::value val) const62 void Signal::set(can::V1_0::CanMessage& msg, Signal::value val) const {
63 CHECK(msg.payload.size() > kLastByte)
64 << "Signal requires message of length " << (kLastByte + 1)
65 << " which is beyond message length of " << msg.payload.size();
66
67 uint8_t firstByte = val << kFirstBit;
68 val >>= kFirstByteBits;
69
70 msg.payload[kFirstByte] = (msg.payload[kFirstByte] & ~kFirstMask) | (firstByte & kFirstMask);
71
72 for (int i = kFirstByte + 1; i < kLastByte; i++) {
73 msg.payload[i] = val & 0xFF;
74 val >>= 8;
75 }
76
77 if (kLastByte != kFirstByte) {
78 msg.payload[kLastByte] = (msg.payload[kLastByte] & ~kLastMask) | (val & kLastMask);
79 }
80 }
81
setDefault(can::V1_0::CanMessage & msg) const82 void Signal::setDefault(can::V1_0::CanMessage& msg) const { set(msg, kDefVal); }
83
84 } // namespace android::hardware::automotive::protocan
85