/* Find the first text record from an NDEF-formatted Ultralight/NTAG2xx tag

and write the text to stdout

*/

#include <bcm2835.h>

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <string.h>

/* Set this to 1 in order to get additional output of what's

going on. Set to 0 to disable spurious output */

#define DEBUG 0

#define SL030_ID 0x50

#define SL030_CMD_SELECT 0x01

#define SL030_READ_PAGE 0x10

#define MAX_TAG_ID_LENGTH 7

#define CMD_BUF_LEN 11

int cmdBufferLen = CMD_BUF_LEN;

unsigned char cmdBuffer[CMD_BUF_LEN];

/* Buffer to hold the contents of the RFID tag */

#define kContentsBufferLen 2048

uint8_t gContentsBuffer[kContentsBufferLen];

struct s_cmdResponse

};

// Constants to make parsing NDEF records easier

#define NDEF_RECORD_MESSAGE_BEGIN (1<<7)

#define NDEF_RECORD_MESSAGE_END (1<<6)

#define NDEF_RECORD_CHUNK_FLAG (1<<5)

#define NDEF_RECORD_SHORT_RECORD (1<<4)

#define NDEF_RECORD_ID_LENGTH_PRESENT (1<<3)

#define NDEF_RECORD_TNF_MASK 0x07

#define NDEF_TNF_EMPTY 0x00

#define NDEF_TNF_NFC_WELL_KNOWN 0x01

#define NDEF_TNF_MEDIA_TYPE_RFC2046 0x02

#define NDEF_TNF_URI_RFC3986 0x03

#define NDEF_TNF_NFC_EXTERNAL 0x04

#define NDEF_TNF_NFC_EXTERNAL 0x04

// NDEF well-known record types

#define NDEF_RTD_TEXT 'T'

#define NDEF_RTD_URI 'U'

#define MIN(a, b) ((a) < (b) ? (a) : (b))

int readPage(int aI2CDevice, char aPage, unsigned char* aTagBuffer, int* aTagBufferLen)

{

int ret = BCM2835_I2C_REASON_ERROR_NACK; // Just needs to be not BCM2835_I2C_REASON_OK

int i;

struct s_cmdResponse* resp;

/* Set up command to select a tag */

cmdBuffer[0] = 2;

cmdBuffer[1] = SL030_READ_PAGE;

cmdBuffer[2] = aPage;

int tries = 0;

while ((tries++ < 12) && (ret != BCM2835_I2C_REASON_OK))

{

bcm2835_i2c_begin();

bcm2835_i2c_setSlaveAddress(SL030_ID);

ret = bcm2835_i2c_write(cmdBuffer, 3);

#if DEBUG

printf("write returned %d\n", ret);

#endif

usleep(12000);

memset(cmdBuffer, 0, CMD_BUF_LEN);

ret = bcm2835_i2c_read(cmdBuffer, cmdBufferLen);

bcm2835_i2c_end();

}

#if DEBUG

printf("read returned %d\n", ret);

for (i = 0; i < cmdBufferLen; i++)

{

printf("%02x ", cmdBuffer[i]);

}

printf("\n");

#endif

resp = (struct s_cmdResponse*)cmdBuffer;

#if DEBUG

printf("Length: %d\n", resp->iLength);

printf("Status: %d\n", resp->iStatus);

printf("Status: %u\n", (char)resp->iStatus);

#endif

if ((resp->iStatus == 0) && (resp->iLength > 2))

{

/* We found a tag! */

/* Copy the ID across */

/* drop 2 bytes from iLength: one each for command and status */

*aTagBufferLen = (resp->iLength - 2 > MAX_TAG_ID_LENGTH ? MAX_TAG_ID_LENGTH : resp->iLength-2);

memcpy(aTagBuffer, resp->iTag, *aTagBufferLen);

return 1;

}

else

{

return 0;

}

}

int checkForTag(int aI2CDevice, unsigned char* aTagBuffer, int* aTagBufferLen)

{

int ret = 0;

int i;

struct s_cmdResponse* resp;

/* Set up command to select a tag */

cmdBuffer[0] = 1;

cmdBuffer[1] = SL030_CMD_SELECT;

bcm2835_i2c_begin();

bcm2835_i2c_setSlaveAddress(SL030_ID);

ret = bcm2835_i2c_write(cmdBuffer, 2);

#if DEBUG

printf("write returned %d\n", ret);

#endif

usleep(20000);

memset(cmdBuffer, 0, CMD_BUF_LEN);

ret = bcm2835_i2c_read(cmdBuffer, cmdBufferLen);

bcm2835_i2c_end();

#if DEBUG

printf("read returned %d\n", ret);

for (i = 0; i < cmdBufferLen; i++)

{

printf("%02x ", cmdBuffer[i]);

}

printf("\n");

#endif

resp = (struct s_cmdResponse*)cmdBuffer;

#if DEBUG

printf("Length: %d\n", resp->iLength);

printf("Status: %d\n", resp->iStatus);

printf("Status: %u\n", (char)resp->iStatus);

#endif

if ((resp->iStatus == 0) && (resp->iLength > 2))

{

/* We found a tag! */

/* Copy the ID across */

/* drop 3 bytes from iLength: one each for command, status and tag type */

*aTagBufferLen = (resp->iLength - 3 > MAX_TAG_ID_LENGTH ? MAX_TAG_ID_LENGTH : resp->iLength-3);

memcpy(aTagBuffer, resp->iTag, *aTagBufferLen);

return 1;

}

else

{

return 0;

}

}

int main(void)

{

int ret;

int fd;

int tries = 0;

int tagIdLen = MAX_TAG_ID_LENGTH;

unsigned char tagId[MAX_TAG_ID_LENGTH];

bcm2835_init();

// We're assuming the caller has made sure there's a tag present

int page = 4; // skip the first four pages as they hold general info on the tag

int pageLen = MAX_TAG_ID_LENGTH;

int contentIdx = 0; // where in the content buffer we're up to

while ((contentIdx < kContentsBufferLen) && readPage(fd, page, &gContentsBuffer[contentIdx], &pageLen))

{

contentIdx += pageLen;

page++; // move onto the next page

}

#if DEBUG

printf("Read in %d bytes\n", contentIdx);

int i;

for (i = 0; i < contentIdx; i++)

{

printf("%02x ", gContentsBuffer[i]);

if (i % 16 == 15)

{

printf("\n");

}

}

printf("\n");

#endif

// Parse the content to look for NDEF records

int idx = 0;

while (idx < contentIdx)

{

// Look for the initial TLV structure

uint8_t t = gContentsBuffer[idx++];

if (t != 0)

{

// It's not a NULL TLV

#if DEBUG

printf("t: %02x\n", t);

#endif

int l = gContentsBuffer[idx++];

idx = MIN(idx, contentIdx);

if (l == 0xff)

{

// 3-byte length format, so the next two bytes are the actual length

l = gContentsBuffer[idx++] << 8 | gContentsBuffer[idx++];

idx = MIN(idx, contentIdx);

}

uint8_t tnf_byte;

uint8_t typeLength =0;

uint32_t payloadLength =0;

uint8_t idLength =0;

int messageEnd = idx + l;

switch (t)

{

case 0x03:

// We've found an NDEF message

// Parse out each record in it

#if DEBUG

printf("NDEF message found\n", t);

#endif

while ((idx < messageEnd) && (idx < contentIdx))

{

tnf_byte = gContentsBuffer[idx++];

idx = MIN(idx, contentIdx);

typeLength = gContentsBuffer[idx++];

idx = MIN(idx, contentIdx);

if (tnf_byte & NDEF_RECORD_SHORT_RECORD)

{

payloadLength = gContentsBuffer[idx++];

}

else

{

payloadLength = (gContentsBuffer[idx++] << 24) |

(gContentsBuffer[idx++] << 16) |

(gContentsBuffer[idx++] << 8) |

(gContentsBuffer[idx++]);

}

idx = MIN(idx, contentIdx);

if (tnf_byte & NDEF_RECORD_ID_LENGTH_PRESENT) {

idLength = gContentsBuffer[idx++];

idx = MIN(idx, contentIdx);

}

#if DEBUG

printf("NDEF record: tnf_byte: 0x%02x, typeLength: %d, idLength: %d, payloadLength: %d, next byte: 0x%02x\n", tnf_byte, typeLength, idLength, payloadLength, gContentsBuffer[idx]);

#endif

// Let's see if it's a record we're interested in...

if ( ((tnf_byte & NDEF_RECORD_TNF_MASK) == NDEF_TNF_NFC_WELL_KNOWN) &&

(typeLength == 1) && (gContentsBuffer[idx] == NDEF_RTD_TEXT) )

{

// It's text! Let's output it...

idx += typeLength; // skip over the type

// skip the language

int langLength = gContentsBuffer[idx++];

payloadLength--; // for the langLength byte

payloadLength -= langLength;

idx += langLength;

while (payloadLength-- > 0)

{

idx = MIN(idx, contentIdx);

printf("%c", gContentsBuffer[idx++]);

}

// ...and quit

exit(0);

}

else

{

// Skip this message

#if DEBUG

printf("Skipping (tnf_byte: %02x)\n", tnf_byte);

printf("idx: %d messageEnd: %d typeLength: %d idLength: %d payloadLength: %d contentIdx: %d\n", idx, messageEnd, typeLength, idLength, payloadLength, contentIdx);

#endif

idx += typeLength+idLength+payloadLength;

idx = MIN(idx, contentIdx);

}

if (tnf_byte & NDEF_RECORD_MESSAGE_END)

{

break;

}

}

break;

case 0xfe:

// Terminator TLV block, give up now

exit(1);

break;

default:

// Skip to the next TLV

idx += l;

break;

};

}

}

}