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1 //-----------------------------------------------------------------------------
2 // This code is licensed to you under the terms of the GNU GPL, version 2 or,
3 // at your option, any later version. See the LICENSE.txt file for the text of
4 // the license.
5 //-----------------------------------------------------------------------------
6 // ISO15693 CRC & other commons
7 //-----------------------------------------------------------------------------
8
9
10 #include "iso15693tools.h"
11
12 #include <stddef.h>
13 #include <stdint.h>
14 #ifdef ON_DEVICE
15 #include "printf.h"
16 #else
17 #include <stdio.h>
18 #endif
19
20
21 #define ISO15693_CRC_PRESET (uint16_t)0xFFFF
22 #define ISO15693_CRC_POLY (uint16_t)0x8408
23
24
25 // The CRC as described in ISO 15693-Part 3-Annex C
26 // v buffer with data
27 // n length
28 // returns crc as 16bit value
29 uint16_t Iso15693Crc(uint8_t *v, int n) {
30 uint32_t reg;
31 int i, j;
32
33 reg = ISO15693_CRC_PRESET;
34 for (i = 0; i < n; i++) {
35 reg = reg ^ ((uint32_t)v[i]);
36 for (j = 0; j < 8; j++) {
37 if (reg & 0x0001) {
38 reg = (reg >> 1) ^ ISO15693_CRC_POLY;
39 } else {
40 reg = (reg >> 1);
41 }
42 }
43 }
44
45 return ~(uint16_t)(reg & 0xffff);
46 }
47
48 // adds a CRC to a dataframe
49 // req[] iso15963 frame without crc
50 // n length without crc
51 // returns the new length of the dataframe.
52 int Iso15693AddCrc(uint8_t *req, int n) {
53 uint16_t crc = Iso15693Crc(req, n);
54 req[n] = crc & 0xff;
55 req[n+1] = crc >> 8;
56 return n + 2;
57 }
58
59
60 // returns a string representation of the UID
61 // UID is transmitted and stored LSB first, displayed MSB first
62 // target char* buffer, where to put the UID, if NULL a static buffer is returned
63 // uid[] the UID in transmission order
64 // return: ptr to string
65 char* Iso15693sprintUID(char *target, uint8_t *uid) {
66 static char tempbuf[2*8+1] = "";
67 if (target == NULL) target = tempbuf;
68 sprintf(target, "%02X%02X%02X%02X%02X%02X%02X%02X", uid[7], uid[6], uid[5], uid[4], uid[3], uid[2], uid[1], uid[0]);
69 return target;
70 }
71
72
73 uint16_t iclass_crc16(uint8_t *data_p, unsigned short length) {
74 unsigned char i;
75 unsigned int data;
76 uint16_t crc = ISO15693_CRC_PRESET;
77
78 if (length == 0)
79 return (~crc);
80
81 do {
82 for (i = 0, data = 0xff & *data_p++; i < 8; i++, data >>= 1) {
83 if ((crc & 0x0001) ^ (data & 0x0001))
84 crc = (crc >> 1) ^ ISO15693_CRC_POLY;
85 else crc >>= 1;
86 }
87 } while (--length);
88
89 crc = ~crc;
90 data = crc;
91 crc = (crc << 8) | (data >> 8 & 0xff);
92 crc = crc ^ 0x0BC3;
93 return (crc);
94 }
95
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