C/C++ - NFC/RFID Bricklet – Tinkerforge

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# 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 "hjw" // Change to your UID

    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 *nfc = (NFCRFID *)user_data;

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

            nfc_rfid_request_tag_id(nfc, current_tag_type);
        }

        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(nfc, &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]);
            }
        }
    }

    int main() {
        // Create ip connection to brickd
        IPConnection ipcon;
        ipcon_create(&ipcon);

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

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

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

        nfc_rfid_request_tag_id(&nfc, NFC_RFID_TAG_TYPE_MIFARE_CLASSIC);

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

### 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 "hjw" // Change to your UID

    // Callback function for state changed callback
    void cb_state_changed(uint8_t state, bool idle, void *user_data) {
        NFCRFID *nfc = (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(nfc, 5, data_write);

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

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

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

            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() {
        // Create ip connection to brickd
        IPConnection ipcon;
        ipcon_create(&ipcon);

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

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

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

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

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

## 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 call by reference. 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

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.

  Current the following tag types are supported:

  - Mifare Classic (`tag_type` = 0)
  - NFC Forum Type 1 (`tag_type` = 1)
  - NFC Forum Type 2 (`tag_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`)
  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.

  Possible states are:

  - Initialization = 0
  - Idle = 128
  - Error = 192
  - RequestTagID = 2
  - RequestTagIDReady = 130
  - RequestTagIDError = 194
  - AuthenticatingMifareClassicPage = 3
  - AuthenticatingMifareClassicPageReady = 131
  - AuthenticatingMifareClassicPageError = 195
  - WritePage = 4
  - WritePageReady = 132
  - WritePageError = 196
  - RequestPage = 5
  - RequestPageReady = 133
  - RequestPageError = 197

  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 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`)
  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_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`)
  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`)
  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`)

  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`)
  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`)
  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 and callbacks it is always disabled.

  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, uint8_t id, void *callback, void *user_data)

  Registers a callback with ID `id` to the function `callback`. The `user_data` will be given as a parameter of the callback.

  The available 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.

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