Libnfc:FAQ

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No NFC device found error

with a UART-based reader

Since v1.7.0, your PN532 UART device needs some configuration in newly introduced configuration file (eg. /etc/nfc/libnfc.conf).
Please read README file, then copy libnfc.conf.sample to the right place.
Make sure to put the file in SYSCONFDIR/nfc/libnfc.conf
If you don't want SYSCONFDIR to be /usr/local/etc, use ./configure --sysconfdir=/etc

with an ACR122U under Windows

Remove ACR122U drivers from ACS

Unable to claim USB interface (Device or resource busy)

You did not read the README!

Udev rules have not been installed...

Too small reply error

With Touchatag or ACR122U

Avoid using pcscd and libnfc with acr122_usb driver all together.
You can stop pcscd or disable support of that reader by pcscd by changing the libccid list of supported readers.

You've to know that those readers are very bad regarding all NFC features and you can expect troubles when using any command not sending immediately a reply: nfc-poll, emulation and p2p modes.

How do I change the libccid list of supported readers?

  • Get the libccid source code;
  • edit the file readers/supported_readers.txt;
  • remove the line with the VID/PID of the reader you want to disable;
  • reinstall the libccid driver, or just the regenerated src/Info.plist.

How to get some communication between a phone and a libnfc reader?

You've basically three options to communicate between phone and libnfc device:

NFC p2p

Check Libllcp

phone emulates a card, libnfc device reads/writes to the card

For PN544 based NFC phones, only possible with a patched Android, e.g. CyanoGenMod 10.1 contains already the required patches.
See e.g. http://nelenkov.blogspot.com/2012/10/emulating-pki-smart-card-with-cm91.html

libnfc device emulates a card, phone reads/writes to the card

Check nfc-emulate-forum-tag2.c and nfc-emulate-forum-tag4.c here: Libnfc:nfc-emulate

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