linux_libnfc-nci

The NFC adaptation layer uses a singleton CNfcConfig to manage settings. It searches for configuration files in a specific order of precedence:

1. Primary Config: It first attempts to load libnfc-nci.conf from the path defined by CONFIG_PATH (the alternative_config_path).
2. Secondary Config: If the primary file is not found or empty, it attempts to load libnfc-nci.conf from /etc/ (the transport_config_path).

Configuration File Format: Settings are defined in a key=value format. Supported value types include:

• Strings: Enclosed in double quotes (e.g., KEY="VALUE").
• Decimals: Standard base-10 numbers (e.g., KEY=123).
• Hexadecimal: Prefixed with 0x (e.g., KEY=0xAB).
• Hex-encoded Strings: Using curly braces {} to represent raw byte sequences (e.g., KEY={0xDE, 0xAD, 0xBE, 0xEF}).

Comments are supported using the # character.

The NXP configuration system uses .conf files. The files are named using the pattern libnfc-nxp-[type].conf where [type] is init, pn547, or pn548.

Search Order:

1. The system first looks in the alternative_config_path (e.g., /data/nfc/ on generic targets or a defined CONFIG_PATH).
2. If not found, it looks in the transport_config_path (e.g., /etc/).

File Syntax:

• Comments: Lines starting with # are ignored.
• Key-Value Pairs: key = value
• String Values: Enclosed in double quotes: key = "value"
• Hexadecimal/Numeric Values: Supports standard numbers and hex notation (e.g., 0x1234).
• Hex-encoded Byte Arrays: Can be represented using {} syntax (e.g., {0xDE, 0xAD, 0xBE, 0xEF}).

To release resources and stop NFC polling, you should deregister all callbacks and disable discovery. The following sequence is recommended:

1. Stop the SNEP server: nfcSnep_stopServer().
2. Disable discovery: nfcManager_disableDiscovery().
3. Deregister all callbacks:
   • nfcSnep_deregisterClientCallback()
   • nfcManager_deregisterTagCallback()
   • nfcHce_deregisterHceCallback()

The demo application provides four primary operational modes via CLI arguments:

1. poll: Activates polling mode to scan for nearby NFC tags.
   • Command: nfcDemoApp poll
2. write: Activates write mode to write NDEF data to a tag.
   • Command: nfcDemoApp write --type=Text -l en -r "Test"
3. push: Activates push mode to send NDEF data to a P2P device.
   • Command: nfcDemoApp push -t URI -u http://www.nxp.com
   • Command (MIME): nfcDemoApp push --type=mime -m "application/vnd.bluetooth.ep.oob" -d "2200AC597405AF1C0E0947616C617879204E6F74652033040D0C024005031E110B11"
4. share: Activates Tag Emulation (HCE) mode to emulate a tag.
   • Command: nfcDemoApp share -t URI -u http://www.nxp.com

To use the device as an NFC tag (Host Card Emulation), register a nfc_host_card_emulation_callback_t structure using nfcHce_registerHceCallback. This allows your application to respond to reader interactions.

Required callback members:

• onDataReceived: Triggered when the NFC reader sends data to the emulated card.
• onHostCardEmulationActivated: Triggered when HCE mode is activated by a reader.
• onHostCardEmulationDeactivated: Triggered when the reader interaction ends.

// Define the callback structure
nfc_host_card_emulation_callback_t g_HceCB;

// Assign functions
g_HceCB.onDataReceived = my_on_hce_data;
g_HceCB.onHostCardEmulationActivated = my_on_hce_activated;
g_HceCB.onHostCardEmulationDeactivated = my_on_hce_deactivated;

// Register with the HCE module
nfcHce_registerHceCallback(&g_HceCB);

Use the GetNumValue C API to retrieve numerical settings (unsigned long, unsigned short, or unsigned char) from the configuration files.

Parameters:

• name: The name of the configuration parameter.
• pValue: A pointer to the memory where the value should be stored.
• len: The size of the memory pointed to by pValue (must match the size of the type you are requesting).

Supported Types (based on len):

• sizeof(unsigned long)
• sizeof(unsigned short)
• sizeof(unsigned char)

Returns:

• true (non-zero) on success.
• false (0) if the parameter is not found or the requested length is invalid.

unsigned long val;
if (GetNumValue("NXP_SOME_NUMERIC_SETTING", &val, sizeof(unsigned long))) {
    // Success: val contains the value
}

For specific tag types like TARGET_TYPE_MIFARE_CLASSIC or TARGET_TYPE_MIFARE_UL, you can use nfcTag_transceive to send custom command buffers and receive responses. This is useful for low-level authentication or reading specific blocks that are not part of the standard NDEF structure.

res = nfcTag_transceive(TagInfo.handle, MifareAuthCmd, 12, MifareAuthResp, 255, 500);

Use GetNxpStrValue to retrieve a string-based configuration parameter from the NXP configuration files. This function searches for the specified name and copies the value into the provided buffer pValue up to the specified len.

// Returns 1 if found, 0 otherwise
int GetNxpStrValue(const char* name, char* pValue, unsigned long len);

Use GetNxpNumValue to retrieve a numerical setting. The function supports different output types based on the len parameter provided. It can handle standard decimal numbers or hex-encoded strings that represent byte sequences.

Supported len values for pValue:

• sizeof(unsigned long)
• sizeof(unsigned short)
• sizeof(unsigned char)

// Returns 1 if successful, 0 otherwise
int GetNxpNumValue(const char* name, void* pValue, unsigned long len);