C/C++ - NFC/RFID Bricklet

This is the description of the C/C++ API bindings for the NFC/RFID Bricklet. General information and technical specifications for the NFC/RFID Bricklet are summarized in its hardware description.

An installation guide for the C/C++ API bindings is part of their general description.

Examples

The example code below is Public Domain (CC0 1.0).

Scan For Tags

Download (example_scan_for_tags.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_nfc_rfid.h"

#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change XYZ to the UID of your NFC/RFID Bricklet

uint8_t current_tag_type = NFC_RFID_TAG_TYPE_MIFARE_CLASSIC;

// Callback function for state changed callback
void cb_state_changed(uint8_t state, bool idle, void *user_data) {
    NFCRFID *nr = (NFCRFID *)user_data;

    if(state == NFC_RFID_STATE_REQUEST_TAG_ID_READY) {
        uint8_t tag_type;
        uint8_t tid_length;
        uint8_t tid[7];

        nfc_rfid_get_tag_id(nr, &tag_type, &tid_length, tid);

        if(tid_length == 4) {
            printf("Found tag of type %d with ID [%x %x %x %x]\n", 
                   tag_type, tid[0], tid[1], tid[2], tid[3]);
        } else {
            printf("Found tag of type %d with ID [%x %x %x %x %x %x %x]\n", 
                   tag_type, tid[0], tid[1], tid[2], tid[3], tid[4], tid[5], tid[6]);
        }
    }

    // Cycle through all types
    if(idle) {
        current_tag_type = (current_tag_type + 1) % 3;

        nfc_rfid_request_tag_id(nr, current_tag_type);
    }
}

int main(void) {
    // Create IP connection
    IPConnection ipcon;
    ipcon_create(&ipcon);

    // Create device object
    NFCRFID nr;
    nfc_rfid_create(&nr, UID, &ipcon);

    // Connect to brickd
    if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
        fprintf(stderr, "Could not connect\n");
        return 1;
    }
    // Don't use device before ipcon is connected

    // Register state changed callback to function cb_state_changed
    nfc_rfid_register_callback(&nr,
                               NFC_RFID_CALLBACK_STATE_CHANGED,
                               (void (*)(void))cb_state_changed,
                               &nr);

    // Start scan loop
    nfc_rfid_request_tag_id(&nr, NFC_RFID_TAG_TYPE_MIFARE_CLASSIC);

    printf("Press key to exit\n");
    getchar();
    nfc_rfid_destroy(&nr);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

Write Read Type2

Download (example_write_read_type2.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_nfc_rfid.h"

#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change XYZ to the UID of your NFC/RFID Bricklet

// Callback function for state changed callback
void cb_state_changed(uint8_t state, bool idle, void *user_data) {
    NFCRFID *nr = (NFCRFID *)user_data;

    (void)idle; // avoid unused parameter warning

    if(state == NFC_RFID_STATE_REQUEST_TAG_ID_READY) {
        printf("Tag found\n");

        // Write 16 byte to pages 5-8
        uint8_t data_write[16] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15};

        nfc_rfid_write_page(nr, 5, data_write);

        printf("Writing data...\n");
    } else if(state == NFC_RFID_STATE_WRITE_PAGE_READY) {
        // Request pages 5-8
        nfc_rfid_request_page(nr, 5);

        printf("Requesting data...\n");
    } else if(state == NFC_RFID_STATE_REQUEST_PAGE_READY) {
        uint8_t data_read[16];

        // Get and print pages 5-8
        nfc_rfid_get_page(nr, data_read);
        printf("Read data: [%d", data_read[0]);

        int i;
        for(i = 1; i < 16; i++) {
            printf(" %d", data_read[i]);
        }

        printf("]\n");
    } else if(state & (1 << 6)) {
        // All errors have bit 6 set
        printf("Error: %d\n", state);
    }
}

int main(void) {
    // Create IP connection
    IPConnection ipcon;
    ipcon_create(&ipcon);

    // Create device object
    NFCRFID nr;
    nfc_rfid_create(&nr, UID, &ipcon);

    // Connect to brickd
    if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
        fprintf(stderr, "Could not connect\n");
        return 1;
    }
    // Don't use device before ipcon is connected

    // Register state changed callback to function cb_state_changed
    nfc_rfid_register_callback(&nr,
                               NFC_RFID_CALLBACK_STATE_CHANGED,
                               (void (*)(void))cb_state_changed,
                               &nr);

    // Select NFC Forum Type 2 tag
    nfc_rfid_request_tag_id(&nr, NFC_RFID_TAG_TYPE_TYPE2);

    printf("Press key to exit\n");
    getchar();
    nfc_rfid_destroy(&nr);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

API

Every function of the C/C++ bindings returns an integer which describes an error code. Data returned from the device, when a getter is called, is handled via output parameters. These parameters are labeled with the ret_ prefix.

Possible error codes are:

  • E_OK = 0
  • E_TIMEOUT = -1
  • E_NO_STREAM_SOCKET = -2
  • E_HOSTNAME_INVALID = -3
  • E_NO_CONNECT = -4
  • E_NO_THREAD = -5
  • E_NOT_ADDED = -6 (unused since bindings version 2.0.0)
  • E_ALREADY_CONNECTED = -7
  • E_NOT_CONNECTED = -8
  • E_INVALID_PARAMETER = -9
  • E_NOT_SUPPORTED = -10
  • E_UNKNOWN_ERROR_CODE = -11
  • E_STREAM_OUT_OF_SYNC = -12
  • E_INVALID_UID = -13

as defined in ip_connection.h.

All functions listed below are thread-safe.

Basic Functions

void nfc_rfid_create(NFCRFID *nfc_rfid, const char *uid, IPConnection *ipcon)

Creates the device object nfc_rfid with the unique device ID uid and adds it to the IPConnection ipcon:

NFCRFID nfc_rfid;
nfc_rfid_create(&nfc_rfid, "YOUR_DEVICE_UID", &ipcon);

This device object can be used after the IP connection has been connected (see examples above).

void nfc_rfid_destroy(NFCRFID *nfc_rfid)

Removes the device object nfc_rfid from its IPConnection and destroys it. The device object cannot be used anymore afterwards.

int nfc_rfid_request_tag_id(NFCRFID *nfc_rfid, uint8_t tag_type)

To read or write a tag that is in proximity of the NFC/RFID Bricklet you first have to call this function with the expected tag type as parameter. It is no problem if you don't know the tag type. You can cycle through the available tag types until the tag gives an answer to the request.

Currently the following tag types are supported:

  • Mifare Classic
  • NFC Forum Type 1
  • NFC Forum Type 2

After you call nfc_rfid_request_tag_id() the NFC/RFID Bricklet will try to read the tag ID from the tag. After this process is done the state will change. You can either register the NFC_RFID_CALLBACK_STATE_CHANGED callback or you can poll nfc_rfid_get_state() to find out about the state change.

If the state changes to RequestTagIDError it means that either there was no tag present or that the tag is of an incompatible type. If the state changes to RequestTagIDReady it means that a compatible tag was found and that the tag ID could be read out. You can now get the tag ID by calling nfc_rfid_get_tag_id().

If two tags are in the proximity of the NFC/RFID Bricklet, this function will cycle through the tags. To select a specific tag you have to call nfc_rfid_request_tag_id() until the correct tag id is found.

In case of any Error state the selection is lost and you have to start again by calling nfc_rfid_request_tag_id().

The following defines are available for this function:

  • NFC_RFID_TAG_TYPE_MIFARE_CLASSIC = 0
  • NFC_RFID_TAG_TYPE_TYPE1 = 1
  • NFC_RFID_TAG_TYPE_TYPE2 = 2
int nfc_rfid_get_tag_id(NFCRFID *nfc_rfid, uint8_t *ret_tag_type, uint8_t *ret_tid_length, uint8_t ret_tid[7])

Returns the tag type, tag ID and the length of the tag ID (4 or 7 bytes are possible length). This function can only be called if the NFC/RFID is currently in one of the Ready states. The returned ID is the ID that was saved through the last call of nfc_rfid_request_tag_id().

To get the tag ID of a tag the approach is as follows:

  1. Call nfc_rfid_request_tag_id()
  2. Wait for state to change to RequestTagIDReady (see nfc_rfid_get_state() or NFC_RFID_CALLBACK_STATE_CHANGED callback)
  3. Call nfc_rfid_get_tag_id()

The following defines are available for this function:

  • NFC_RFID_TAG_TYPE_MIFARE_CLASSIC = 0
  • NFC_RFID_TAG_TYPE_TYPE1 = 1
  • NFC_RFID_TAG_TYPE_TYPE2 = 2
int nfc_rfid_get_state(NFCRFID *nfc_rfid, uint8_t *ret_state, bool *ret_idle)

Returns the current state of the NFC/RFID Bricklet.

On startup the Bricklet will be in the Initialization state. The initialization will only take about 20ms. After that it changes to Idle.

The functions of this Bricklet can be called in the Idle state and all of the Ready and Error states.

Example: If you call nfc_rfid_request_page(), the state will change to RequestPage until the reading of the page is finished. Then it will change to either RequestPageReady if it worked or to RequestPageError if it didn't. If the request worked you can get the page by calling nfc_rfid_get_page().

The same approach is used analogously for the other API functions.

The following defines are available for this function:

  • NFC_RFID_STATE_INITIALIZATION = 0
  • NFC_RFID_STATE_IDLE = 128
  • NFC_RFID_STATE_ERROR = 192
  • NFC_RFID_STATE_REQUEST_TAG_ID = 2
  • NFC_RFID_STATE_REQUEST_TAG_ID_READY = 130
  • NFC_RFID_STATE_REQUEST_TAG_ID_ERROR = 194
  • NFC_RFID_STATE_AUTHENTICATING_MIFARE_CLASSIC_PAGE = 3
  • NFC_RFID_STATE_AUTHENTICATING_MIFARE_CLASSIC_PAGE_READY = 131
  • NFC_RFID_STATE_AUTHENTICATING_MIFARE_CLASSIC_PAGE_ERROR = 195
  • NFC_RFID_STATE_WRITE_PAGE = 4
  • NFC_RFID_STATE_WRITE_PAGE_READY = 132
  • NFC_RFID_STATE_WRITE_PAGE_ERROR = 196
  • NFC_RFID_STATE_REQUEST_PAGE = 5
  • NFC_RFID_STATE_REQUEST_PAGE_READY = 133
  • NFC_RFID_STATE_REQUEST_PAGE_ERROR = 197
int nfc_rfid_authenticate_mifare_classic_page(NFCRFID *nfc_rfid, uint16_t page, uint8_t key_number, uint8_t key[6])

Mifare Classic tags use authentication. If you want to read from or write to a Mifare Classic page you have to authenticate it beforehand. Each page can be authenticated with two keys: A (key_number = 0) and B (key_number = 1). A new Mifare Classic tag that has not yet been written to can be accessed with key A and the default key [0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF].

The approach to read or write a Mifare Classic page is as follows:

  1. Call nfc_rfid_request_tag_id()
  2. Wait for state to change to RequestTagIDReady (see nfc_rfid_get_state() or NFC_RFID_CALLBACK_STATE_CHANGED callback)
  3. If looking for a specific tag then call nfc_rfid_get_tag_id() and check if the expected tag was found, if it was not found go back to step 1
  4. Call nfc_rfid_authenticate_mifare_classic_page() with page and key for the page
  5. Wait for state to change to AuthenticatingMifareClassicPageReady (see nfc_rfid_get_state() or NFC_RFID_CALLBACK_STATE_CHANGED callback)
  6. Call nfc_rfid_request_page() or nfc_rfid_write_page() to read/write page

The following defines are available for this function:

  • NFC_RFID_KEY_A = 0
  • NFC_RFID_KEY_B = 1
int nfc_rfid_write_page(NFCRFID *nfc_rfid, uint16_t page, uint8_t data[16])

Writes 16 bytes starting from the given page. How many pages are written depends on the tag type. The page sizes are as follows:

  • Mifare Classic page size: 16 byte (one page is written)
  • NFC Forum Type 1 page size: 8 byte (two pages are written)
  • NFC Forum Type 2 page size: 4 byte (four pages are written)

The general approach for writing to a tag is as follows:

  1. Call nfc_rfid_request_tag_id()
  2. Wait for state to change to RequestTagIDReady (see nfc_rfid_get_state() or NFC_RFID_CALLBACK_STATE_CHANGED callback)
  3. If looking for a specific tag then call nfc_rfid_get_tag_id() and check if the expected tag was found, if it was not found got back to step 1
  4. Call nfc_rfid_write_page() with page number and data
  5. Wait for state to change to WritePageReady (see nfc_rfid_get_state() or NFC_RFID_CALLBACK_STATE_CHANGED callback)

If you use a Mifare Classic tag you have to authenticate a page before you can write to it. See nfc_rfid_authenticate_mifare_classic_page().

int nfc_rfid_request_page(NFCRFID *nfc_rfid, uint16_t page)

Reads 16 bytes starting from the given page and stores them into a buffer. The buffer can then be read out with nfc_rfid_get_page(). How many pages are read depends on the tag type. The page sizes are as follows:

  • Mifare Classic page size: 16 byte (one page is read)
  • NFC Forum Type 1 page size: 8 byte (two pages are read)
  • NFC Forum Type 2 page size: 4 byte (four pages are read)

The general approach for reading a tag is as follows:

  1. Call nfc_rfid_request_tag_id()
  2. Wait for state to change to RequestTagIDReady (see nfc_rfid_get_state() or NFC_RFID_CALLBACK_STATE_CHANGED callback)
  3. If looking for a specific tag then call nfc_rfid_get_tag_id() and check if the expected tag was found, if it was not found got back to step 1
  4. Call nfc_rfid_request_page() with page number
  5. Wait for state to change to RequestPageReady (see nfc_rfid_get_state() or NFC_RFID_CALLBACK_STATE_CHANGED callback)
  6. Call nfc_rfid_get_page() to retrieve the page from the buffer

If you use a Mifare Classic tag you have to authenticate a page before you can read it. See nfc_rfid_authenticate_mifare_classic_page().

int nfc_rfid_get_page(NFCRFID *nfc_rfid, uint8_t ret_data[16])

Returns 16 bytes of data from an internal buffer. To fill the buffer with specific pages you have to call nfc_rfid_request_page() beforehand.

Advanced Functions

int nfc_rfid_get_api_version(NFCRFID *nfc_rfid, uint8_t ret_api_version[3])

Returns the version of the API definition (major, minor, revision) implemented by this API bindings. This is neither the release version of this API bindings nor does it tell you anything about the represented Brick or Bricklet.

int nfc_rfid_get_response_expected(NFCRFID *nfc_rfid, uint8_t function_id, bool *ret_response_expected)

Returns the response expected flag for the function specified by the function ID parameter. It is true if the function is expected to send a response, false otherwise.

For getter functions this is enabled by default and cannot be disabled, because those functions will always send a response. For callback configuration functions it is enabled by default too, but can be disabled by nfc_rfid_set_response_expected(). For setter functions it is disabled by default and can be enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

See nfc_rfid_set_response_expected() for the list of function ID defines available for this function.

int nfc_rfid_set_response_expected(NFCRFID *nfc_rfid, uint8_t function_id, bool response_expected)

Changes the response expected flag of the function specified by the function ID parameter. This flag can only be changed for setter (default value: false) and callback configuration functions (default value: true). For getter functions it is always enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

The following function ID defines are available for this function:

  • NFC_RFID_FUNCTION_REQUEST_TAG_ID = 1
  • NFC_RFID_FUNCTION_AUTHENTICATE_MIFARE_CLASSIC_PAGE = 4
  • NFC_RFID_FUNCTION_WRITE_PAGE = 5
  • NFC_RFID_FUNCTION_REQUEST_PAGE = 6
int nfc_rfid_set_response_expected_all(NFCRFID *nfc_rfid, bool response_expected)

Changes the response expected flag for all setter and callback configuration functions of this device at once.

int nfc_rfid_get_identity(NFCRFID *nfc_rfid, char ret_uid[8], char ret_connected_uid[8], char *ret_position, uint8_t ret_hardware_version[3], uint8_t ret_firmware_version[3], uint16_t *ret_device_identifier)

Returns the UID, the UID where the Bricklet is connected to, the position, the hardware and firmware version as well as the device identifier.

The position can be 'a', 'b', 'c' or 'd'.

The device identifier numbers can be found here. There is also a constant for the device identifier of this Bricklet.

Callback Configuration Functions

void nfc_rfid_register_callback(NFCRFID *nfc_rfid, int16_t callback_id, void (*function)(void), void *user_data)

Registers the given function with the given callback_id. The user_data will be passed as the last parameter to the function.

The available callback IDs with corresponding function signatures are listed below.

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the nfc_rfid_register_callback() function. The parameters consist of the device object, the callback ID, the callback function and optional user data:

void my_callback(int p, void *user_data) {
    printf("parameter: %d\n", p);
}

nfc_rfid_register_callback(&nfc_rfid, NFC_RFID_CALLBACK_EXAMPLE, (void *)my_callback, NULL);

The available constants with corresponding callback function signatures are described below.

Note

Using callbacks for recurring events is always preferred compared to using getters. It will use less USB bandwidth and the latency will be a lot better, since there is no round trip time.

NFC_RFID_CALLBACK_STATE_CHANGED
void callback(uint8_t state, bool idle, void *user_data)

This callback is called if the state of the NFC/RFID Bricklet changes. See nfc_rfid_get_state() for more information about the possible states.

The following defines are available for this function:

  • NFC_RFID_STATE_INITIALIZATION = 0
  • NFC_RFID_STATE_IDLE = 128
  • NFC_RFID_STATE_ERROR = 192
  • NFC_RFID_STATE_REQUEST_TAG_ID = 2
  • NFC_RFID_STATE_REQUEST_TAG_ID_READY = 130
  • NFC_RFID_STATE_REQUEST_TAG_ID_ERROR = 194
  • NFC_RFID_STATE_AUTHENTICATING_MIFARE_CLASSIC_PAGE = 3
  • NFC_RFID_STATE_AUTHENTICATING_MIFARE_CLASSIC_PAGE_READY = 131
  • NFC_RFID_STATE_AUTHENTICATING_MIFARE_CLASSIC_PAGE_ERROR = 195
  • NFC_RFID_STATE_WRITE_PAGE = 4
  • NFC_RFID_STATE_WRITE_PAGE_READY = 132
  • NFC_RFID_STATE_WRITE_PAGE_ERROR = 196
  • NFC_RFID_STATE_REQUEST_PAGE = 5
  • NFC_RFID_STATE_REQUEST_PAGE_READY = 133
  • NFC_RFID_STATE_REQUEST_PAGE_ERROR = 197

Constants

NFC_RFID_DEVICE_IDENTIFIER

This constant is used to identify a NFC/RFID Bricklet.

The nfc_rfid_get_identity() function and the IPCON_CALLBACK_ENUMERATE callback of the IP Connection have a device_identifier parameter to specify the Brick's or Bricklet's type.

NFC_RFID_DEVICE_DISPLAY_NAME

This constant represents the human readable name of a NFC/RFID Bricklet.