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| Rev | Author | Line No. | Line |
|---|---|---|---|
| 2 | mjames | 1 | /* |
| 2 | * nmea.c |
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| 3 | * |
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| 4 | * Created on: 6 Sep 2020 |
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| 5 | * Author: mike |
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| 6 | */ |
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| 7 | |||
| 4 | mjames | 8 | #include <math.h> |
| 9 | #include <stdint.h> |
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| 10 | #include <stdlib.h> |
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| 11 | |||
| 2 | mjames | 12 | #include "nmea.h" |
| 13 | |||
| 14 | #include "libSerial/serial.h" |
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| 15 | |||
| 16 | char linebuff[80]; |
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| 17 | unsigned linePos = 0; |
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| 18 | |||
| 19 | typedef enum |
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| 20 | { |
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| 21 | SEARCH, READING |
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| 22 | } NmeaState_t; |
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| 23 | |||
| 24 | NmeaState_t lineState = SEARCH; |
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| 25 | |||
| 4 | mjames | 26 | static uint8_t |
| 2 | mjames | 27 | decodePacket (char *linebuff, int linePos, Location *loc); |
| 28 | |||
| 29 | uint8_t |
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| 30 | updateLocation (Location *loc) |
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| 31 | { |
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| 32 | while (1) |
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| 33 | { |
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| 34 | if (!SerialCharsReceived (&uc1)) |
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| 35 | return false; // nothing to read, return immediately |
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| 36 | |||
| 37 | char c = GetCharSerial (&uc1); |
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| 38 | switch (lineState) |
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| 39 | { |
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| 40 | case SEARCH: |
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| 41 | if (c == '$') |
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| 42 | lineState = READING; |
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| 43 | break; |
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| 44 | case READING: |
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| 45 | if (c == '\r') |
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| 46 | { |
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| 47 | // handle the read code |
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| 48 | uint8_t success = decodePacket (linebuff, linePos, loc); |
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| 49 | lineState = SEARCH; |
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| 50 | |||
| 51 | linePos = 0; |
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| 52 | return success; |
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| 53 | } |
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| 54 | if (linePos < sizeof(linebuff)) |
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| 55 | linebuff[linePos++] = c; |
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| 56 | else |
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| 57 | { |
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| 58 | linePos = 0; |
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| 59 | lineState = SEARCH; |
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| 60 | } |
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| 61 | break; |
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| 62 | } |
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| 63 | } |
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| 64 | return 0; |
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| 65 | } |
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| 66 | |||
| 4 | mjames | 67 | static uint8_t |
| 2 | mjames | 68 | decodeHex (char c) |
| 69 | { |
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| 70 | if (c >= '0' && c <= '9') |
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| 71 | return c - '0'; |
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| 72 | c = tolower (c); |
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| 73 | if (c >= 'a' && c <= 'f') |
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| 74 | return c - 'a' + 10; |
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| 75 | return 0; |
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| 76 | } |
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| 77 | |||
| 4 | mjames | 78 | // lat/long decoder |
| 79 | static float |
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| 80 | decodeLL (char *ptr, int msDigitWeight) |
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| 81 | { |
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| 82 | float digitWeight = msDigitWeight; |
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| 83 | float result = 0; |
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| 84 | int i = 0; |
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| 85 | while (1) |
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| 86 | { |
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| 87 | char c = ptr[i++]; |
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| 88 | if (c == '.') |
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| 89 | continue; |
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| 90 | if (c >= '0' && c <= '9') |
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| 91 | { |
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| 92 | result += digitWeight * (c - '0'); |
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| 93 | if (fabs (digitWeight - 1) < 0.01) |
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| 94 | digitWeight = 1 / 6.0; |
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| 95 | else |
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| 96 | digitWeight = digitWeight / 10; |
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| 97 | |||
| 98 | continue; |
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| 99 | } |
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| 100 | break; |
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| 101 | } |
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| 102 | |||
| 103 | return result; |
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| 104 | |||
| 105 | } |
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| 106 | |||
| 107 | static float decodeFP(char * ptr) |
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| 108 | { |
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| 109 | return strtof(ptr,NULL); |
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| 110 | } |
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| 111 | |||
| 2 | mjames | 112 | uint8_t |
| 113 | decodePacket (char *linebuff, int linePos, Location *loc) |
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| 114 | { |
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| 5 | mjames | 115 | uint8_t checksum = 0; |
| 2 | mjames | 116 | for (int i = 0; i < linePos - 3; i++) |
| 117 | checksum ^= linebuff[i]; |
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| 118 | uint8_t givenSum = (decodeHex (linebuff[linePos - 2]) << 4) |
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| 119 | + decodeHex (linebuff[linePos - 1]); |
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| 120 | if (givenSum != checksum) |
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| 121 | return 0; |
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| 122 | |||
| 123 | char *fieldPos[20]; |
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| 124 | int fieldCnt = 0; |
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| 125 | // split fields |
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| 4 | mjames | 126 | for (int i = 5; i < linePos - 3; i++) |
| 2 | mjames | 127 | { |
| 128 | if (linebuff[i] == ',') |
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| 129 | { |
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| 130 | fieldPos[fieldCnt++] = linebuff + i + 1; |
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| 131 | } |
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| 4 | mjames | 132 | |
| 2 | mjames | 133 | } |
| 134 | |||
| 4 | mjames | 135 | if (linebuff[2] == 'R' && linebuff[3] == 'M' && linebuff[4] == 'C') |
| 2 | mjames | 136 | |
| 137 | { |
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| 3 | mjames | 138 | // decode the fields |
| 4 | mjames | 139 | loc->valid = *fieldPos[1]; |
| 140 | loc->lat = decodeLL (fieldPos[2], 10); |
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| 141 | loc->ns = *fieldPos[3]; |
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| 142 | loc->lon = decodeLL (fieldPos[4], 100); |
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| 143 | loc->ew = *fieldPos[5]; |
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| 144 | loc->speed = decodeFP (fieldPos[6]); |
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| 145 | loc->heading = decodeFP (fieldPos[7]); |
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| 3 | mjames | 146 | |
| 4 | mjames | 147 | } |
| 5 | mjames | 148 | return linePos; |
| 2 | mjames | 149 | } |