T4T NDEF emulation example reads only 134 bytes on NFC reader (PN7160)

[Niranjan123]

Hello Team,

I am using the NXP linux_libnfc-nci t4t-ndef-emulation_example with PN7160.

Reference example:
https://github.com/NXPNFCLinux/linux_libnfc-nci_examples/tree/master/t4t-ndef-emulation_example

Use case

• One board acts as Type-4 Tag (T4T) and shares log data

• Another board acts as NFC reader

• Goal is to retrieve log data (< 8 KB) over NFC

Issue

My application is able to write log data successfully (for example > 200 bytes),
but on the NFC reader side, it always reads maximum 134 bytes only.

Reader output shows:

NDEF Content Max size : 134 bytes

Even when more data is written, the reader does not read beyond this size.

Questions

1. Is the t4t-ndef-emulation_example limited to 134 bytes by design?

2. Are there any additional stack changes required to support larger NDEF sizes (< 8 KB)?

3. Is there any reference patch or documentation from NXP for increasing the T4T NDEF size?
   
   
   

   Any guidance it will be helpful.

   Thanks.
   
   
   Regards,
   Niranjan
   
   

[Fabian_R]

Hello, 

Thank you for your interest in our products.

Regarding your first question, my understanding is that your application is able to log data >200 Bytes. Are you able to fully read it by using another reader?

As you may have noticed, the examples for the Library are only showing how to implement either the emulation or the reading of the emulated tag. The only limitation of the NDEF size is the specification. Please keep in mind that in order to create and read an NDEF file larger than 255 bytes, it is necessary to configure the respective flags as required.

Regarding the implementation of reading a large message, please note that you will need to review the respective specifications.

• The T4T Specification, to successfully build the Emulated NDEF message as a File.

• The NDEF Specification for correctly building a Large NDEF.

Since these specifications have to be purchased, we aren't allowed to disclose further information. 

If you need further support in the implementation of the examples, please share your implementations with us. I'll be happy to take a look and provide some specific recommendations.

[Niranjan123]

Hello,

Thank you for your response.

Yes, our application is able to generate and store log data greater than 200 bytes.
We are attaching our current implementation (log_data.zip) based on the t4t-ndef-emulation_example for your reference.

On the reader side, we are using nfcDemoApp poll, which is also based on the linux_libnfc-nci stack.

Our requirement is to retrieve log data (< 8 KB) from a device acting as a Type-4 Tag, using another NFC reader running the same stack.

Currently, even after attempting to construct a larger NDEF message, the reader always reports:

NDEF Content Max size : 134 bytes

and does not read beyond this size.

We understand that for NDEF payloads larger than 255 bytes, the appropriate flags must be configured as per the NDEF specification. However, with the current example and stack, we are unable to read NDEF data larger than this limit.

Could you please help clarify:

• Whether the t4t-ndef-emulation_example officially supports large NDEF files (>255 bytes)

• Whether nfcDemoApp poll supports reading large NDEF records created by the emulation example

• If any additional configuration or stack-level changes are required when using linux_libnfc-nci for this use case

Please let us know if any specific changes are needed in the example code. We would appreciate your guidance.

Best regards,
Niranjan

[Fabian_R]

Hello sir,

Since the function nfcTag_writeNdef() has as a parameter the unsigned int type of ndef_buffer_length. The theoretical length of the NDEF should comply with the NDEF Specification.

After performing the writeNDEF, are you able to get the length value from the actual Host (Not using NFC interface), just the I2C Host?

Regarding your second question, why are you using nfcDemoApp? This example is intended for PN7150, not PN7160. Have you tried using tag-read_example for PN7160?  linux_libnfc-nci_examples/tag-read_example at master · NXPNFCLinux/linux_libnfc-nci_examples · GitHu...

I hope this information may have been useful.