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zenyagami/BlePechak.kt

Created March 25, 2026 15:12
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Pecham BLE sensor
Raw
BlePechak.kt
package com.zenthek.autozen.tpms.data.vehicle.bluetooth.model
import android.bluetooth.le.ScanRecord
import android.bluetooth.le.ScanResult
import com.zenthek.autozen.tpms.common.now
import com.zenthek.autozen.tpms.data.vehicle.model.Pressure.CREATOR.psi
import com.zenthek.autozen.tpms.data.vehicle.model.Temperature.CREATOR.celsius
import com.zenthek.autozen.tpms.data.vehicle.model.Tyre
import timber.log.Timber
import java.nio.ByteBuffer
import java.nio.ByteOrder
@OptIn(ExperimentalStdlibApi::class)
@Suppress("DataClassPrivateConstructor")
internal data class RawPecham private constructor(
private val macAddress: String,
private val rssi: Int,
private val data: ByteArray
) : Raw {
private fun id() = macAddress.hashCode()
private fun pressure() = data
.copyOfRange(3, 5)
.let {
ByteBuffer.wrap(it)
.order(ByteOrder.BIG_ENDIAN)
.getShort()
}
.div(10f)
.minus(15f) // fix the issue with wrong psi, always minus 15 apparently
.psi.also { Timber.d("tpms psi value $it kpa? ${it.kpa}") }
private fun battery() = data[1].toUShort() // Returns 27 for 2.7 volts
private fun temperature() = data[2].toFloat().celsius
override fun asTyre() = Tyre.Unlocated(
now(),
rssi,
id(),
pressure(),
temperature(),
battery(),
battery() < 26u // Mimics the alarm from the official app
)
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (javaClass != other?.javaClass) return false
other as RawPecham
if (macAddress != other.macAddress) return false
return data.contentEquals(other.data)
}
override fun hashCode(): Int {
var result = macAddress.hashCode()
result = 31 * result + data.contentHashCode()
return result
}
companion object {
operator fun invoke(result: ScanResult): RawPecham? {
val scanRecord = result.scanRecord
?: return null
if (scanRecord.deviceName != "BR") {
return null
}
if (CRC.isValid(scanRecord).not()) {
return null
}
// Calling result.scanRecord?.manufacturerSpecificData?.valueAt(0) will not work because
// the returned array is 5 bytes only instead of 7 bytes. It doesn't contain the first 2
// bytes
Timber.d("tpms scanRecord raw ${scanRecord.bytes.toHexString()}")
val data = runCatching { scanRecord.bytes.copyOfRange(10, 17) }
.onFailure {
Timber.i(it, "Filled bytes are incorrect: $${scanRecord.bytes.toHexString()}")
}
.getOrNull()
?: return null
return RawPecham(result.device.address, result.rssi, data)
}
private object CRC {
fun isValid(scanRecord: ScanRecord): Boolean {
val dataWithCRC = scanRecord.bytes
val (highByteIndex, lowByteIndex) = bytes(
dataWithCRC.take(dataWithCRC.size - 2).toByteArray()
)
return auchCRCHi[highByteIndex] == dataWithCRC[15] && auchCRCLo[lowByteIndex] == dataWithCRC[16]
}
private fun bytes(dataWithoutCRC: ByteArray): Pair<Int, Int> =
calculate(data = dataWithoutCRC)
.let { (it shr 8 and 0xFF) to (it and 0xFF) }
// Reverse engineered with the help of ChatGPT
private fun calculate(
polynomial: Int = 32773,
initialValue: Int = 65535,
data: ByteArray,
startIndex: Int = 0,
length: Int = 15,
reverseData: Boolean = false,
reverseResult: Boolean = false,
finalXOR: Int = 0
): Int {
var crcValue = initialValue
var dataIndex = startIndex
while (dataIndex < startIndex + length && dataIndex < data.size) {
val currentByte = data[dataIndex]
var bitOrder: Int
var crcTemp = crcValue
for (bitIndex in 0..7) {
bitOrder = if (reverseData) {
7 - bitIndex
} else {
bitIndex
}
var crcMSB = true
val dataBit: Boolean = currentByte.toInt() shr (7 - bitOrder) and 1 == 1
if (crcTemp shr 15 and 1 != 1) {
crcMSB = false
}
val shiftedCRC = crcTemp shl 1
crcTemp = shiftedCRC
if (dataBit xor crcMSB) {
crcTemp = shiftedCRC xor polynomial
}
}
++dataIndex
crcValue = crcTemp
}
return if (reverseResult) Integer.reverse(crcValue) ushr 16 xor finalXOR else crcValue xor finalXOR and 65535
}
private val auchCRCHi = byteArrayOf(
-115,
113,
-89,
0,
-43,
118,
54,
-74,
108,
126,
94,
-15,
86,
91,
-123,
-75,
-72,
-92,
1,
-59,
53,
-20,
-90,
10,
-22,
107,
117,
-90,
79,
-106,
82,
-57,
-73,
43,
-103,
-84,
-43,
-36,
-66,
66,
39,
-29,
-107,
-22,
-72,
-50,
-75,
-93,
-106,
-124,
114,
127,
64,
111,
-110,
-78,
-118,
-85,
-108,
54,
45,
111,
-80,
123,
38,
-66,
-110,
-122,
-32,
-123,
-64,
66,
22,
-75,
-40,
-22,
109,
-11,
-38,
-108,
117,
-7,
43,
-105,
15,
23,
85,
97,
-94,
89,
64,
94,
47,
-76,
116,
-119,
115,
15,
-41,
15,
-41,
-18,
56,
36,
87,
75,
-57,
-31,
47,
-25,
-125,
-112,
-28,
-83,
-74,
6,
-100,
77,
127,
-105,
-65,
52,
48,
26,
48,
-24,
-64,
-15,
-48,
-80,
-88,
69,
53,
-37,
31,
-87,
91,
-63,
70,
-98,
106,
-44,
15,
8,
119,
-84,
100,
-28,
99,
-29,
-44,
62,
8,
105,
-116,
-51,
46,
-8,
-9,
122,
-8,
101,
26,
-107,
-90,
77,
122,
-17,
111,
121,
40,
18,
-19,
44,
-108,
58,
27,
-112,
-115,
-72,
124,
-25,
9,
-102,
-44,
-124,
97,
99,
-78,
28,
-19,
-60,
92,
-33,
10,
-25,
1,
53,
87,
-77,
3,
-127,
52,
97,
6,
-6,
6,
-83,
45,
-26,
83,
-102,
111,
-106,
25,
48,
-92,
-64,
73,
24,
-85,
104,
-110,
-50,
94,
-87,
2,
-79,
54,
20,
-45,
-86,
-52,
7,
-83,
120,
5,
-84,
-57,
21,
127,
-92,
-33,
10,
-32,
8,
76,
-53,
-93,
76,
99,
32,
-115,
-64,
-102,
59
)
private val auchCRCLo = byteArrayOf(
32,
-64,
-63,
17,
-61,
3,
2,
-62,
-58,
126,
127,
-65,
125,
-67,
-68,
124,
-52,
12,
13,
-51,
15,
-49,
-50,
14,
10,
-54,
-53,
11,
-55,
9,
8,
-56,
-100,
92,
93,
-99,
95,
-97,
-98,
94,
90,
-102,
-101,
91,
-103,
89,
88,
-104,
-40,
24,
25,
-39,
27,
-37,
-38,
26,
30,
-34,
-33,
31,
-35,
29,
28,
-36,
20,
-44,
-43,
21,
-41,
23,
22,
-42,
-46,
18,
19,
-45,
17,
-47,
-48,
16,
-16,
48,
49,
-15,
51,
-13,
-14,
50,
54,
-10,
-9,
55,
-11,
53,
52,
-12,
60,
-4,
-3,
61,
-1,
63,
62,
-2,
-6,
58,
59,
-5,
57,
-7,
-8,
56,
40,
-24,
-23,
41,
-21,
43,
42,
-22,
-18,
46,
47,
-17,
45,
-19,
-20,
44,
-28,
36,
37,
-27,
39,
-25,
-26,
38,
34,
-30,
-29,
35,
-31,
33,
32,
-32,
-120,
72,
73,
-119,
75,
-117,
-118,
74,
78,
-114,
-113,
79,
-115,
77,
76,
-116,
-96,
96,
97,
-95,
99,
-93,
-94,
98,
102,
-90,
-89,
103,
-91,
101,
100,
-92,
108,
-84,
-83,
109,
-81,
111,
110,
-82,
-86,
106,
107,
-85,
105,
-87,
-88,
104,
120,
-72,
-71,
121,
-69,
123,
122,
-70,
-66,
126,
127,
-58,
6,
7,
-57,
5,
-76,
116,
117,
-75,
119,
-73,
-74,
118,
114,
-78,
-77,
115,
-79,
113,
112,
-80,
80,
-112,
-109,
81,
-109,
83,
82,
-110,
-106,
86,
87,
-105,
85,
-107,
-108,
84,
68,
-124,
-123,
69,
-121,
71,
70,
-122,
-126,
66,
67,
-125,
65,
-127,
-128,
64
)
}
}
}
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