• rconty
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  • Registered: 2009-04-22
  • Posts: 673

Topic: Why ACR122 devices are not recommended with libnfc ?

Hello,

As there are many users who ask about ACR122, I would like to clarify why this is a bad idea to use ACR122 (and derivated like Touchatag), at least with libnfc.

First, I have to say these devices are well-packaged, are cheap, have a nice look and work perfectly as RFID @13.56Mhz reader using PC/SC on common platforms as these devices are CCID compliant.

Internally, an ACR122 device is made with an MCU, a NFC chip (PN532) and an antenna.
MCU made the device CCID compliant and provide an USB connection.

Now let's talk about NFC and underlying requierements: to do more than RFID reader, you will need to:
- Poll for different targets (NFC-A, NFC-B, NFC-F and DEP)
- Act as target in ISO/IEC 14443-4 emulation mode (optionnal regarding NFC Forum but very useful to be backward compatible with device that are not able to do P2P)
- Do P2P as defined in "Logical Link Control Protocal" (LLCP) from NFC-Forum

Polling and acting as target need to be cancellable, ie. you start a target emulation but no initiator comes, you will have to abort the target emulation.
Next, LLCP defines some timeouts for command sending/receiving but long timeouts relies on "abortable" commands.

In actual architecture, libnfc directly talk to NFC Chip (PN532).
To do that, libnfc's ACR122 driver passthrough PC/SC (and internal MCU) by using some special commands that allow to send frames directly to the PN532.
So with ACR122, the libnfc relies on PC/SC but there is no timeout on command and no way to cancel a running command in PC/SC API.

Conclusion, we can't do reliable and robust NFC with ACR122 and libnfc.

Of course, any contributions are more than welcome to fully support ACR122 devices in libnfc.

Romuald Conty
  • Registered: 2011-11-09
  • Posts: 4

Re: Why ACR122 devices are not recommended with libnfc ?

Hi Romuald, this post clarify many things about this nfc device, because as you said is popular and cheap.

But, the acr122 it's the same as the acr122u? I know that acr122 was launched in 2009 and acr122u a few months ago, there's any improvement in acr122u?

Also, wich model of nfc device reader do you recommend?

thanks a lot

  • rconty
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  • Registered: 2009-04-22
  • Posts: 673

Re: Why ACR122 devices are not recommended with libnfc ?

kavastudios wrote:

But, the acr122 it's the same as the acr122u?

Yes, ACR122U is a "new" ACR122 version (understand less bogus than before).

kavastudios wrote:

Also, which model of nfc device reader do you recommend?

ATM, SCL3711 from SCM and StickID from SensorID are the best choice for doing NFC with libnfc.

If you don't need a case, ie. made a NFC kiosk, the best choice is the opensource PN532 breakout board from microbuilder.eu (now sold at adafruit).

http://www.libnfc.org/documentation/har … patibility

Romuald Conty
  • Registered: 2012-03-07
  • Posts: 2

Re: Why ACR122 devices are not recommended with libnfc ?

rconty wrote:

ATM, SCL3711 from SCM and StickID from SensorID are the best choice for doing NFC with libnfc.


Hi! Where i can purchase StickID device? I'm italian, as the producer of this device, but  on their site there isn't a commercial section..

Last edited by pavlon (2012-03-08 08:30:39)

  • Registered: 2012-05-16
  • Posts: 1

Re: Why ACR122 devices are not recommended with libnfc ?

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