ST25R: Unable to communicate via NFC-V

[stepanoplustil]

Hello,

I'm running a demo from STSW-ST25R-LIB which uses NFC-V. The Inventory poll returns RFAL_ERR_FRAMING as the SOF does not match. Also I have to push the tag really close to get this behaviour. The tag (M24LR64) should be fine as I can communicate with it via ST25 Android app.

I assume that my HW and rfal_platform.h is set right as NFC-A tag is found successfuly after enabling it via RFAL_FEATURE_NFCA.

HW I'm using is EFM32 development board with click shield and NFC 5 Click module by Mikroe.

I have following questions:

Is it possible that the board layout is problematic for NFC-V, but NFC-A is fine?

Is it possible that the chip itself could be faulty and behave like this?

I found macro RFAL_USE_COHE. Could this help? I have not found any information about this.

Is there anything else that could cause this problem?

Thank you very much for help or suggestions!

[Ulysses HERNIOSUS]

Hi,

I assume you are using the ST25R3916 (X-NUCLEO-NFC06A1)?

I could imagine that in your case the strong coupling may amplify some noise (from card/power supply) to be recognized as additional modulation from the card. At the beginning of a message the gain is typically at highest and AGC may not be fast enough filtering out noise in the beginning. 

I expect RFAL_USE_COHE to not having an effect as I expect default analog config not being used. And even if you move to coherent you may actually worsen the situation. 

I would do the following:

1. Look at the actual error in VICCDecode: Is it already failing at SOF, with which data byte?
2. Enable IQ demodulator which should give more noise resistance. This could also be activated for other protocols
3. Increase the gain reduction, play with values to find a good compromise

The necessary changes are detailed here:

diff --git a/source/rfal_iso15693_2.c b/source/rfal_iso15693_2.c
index cf9f5e07..10fd9061 100644
--- a/source/rfal_iso15693_2.c
+++ b/source/rfal_iso15693_2.c
@@ -297,7 +297,7 @@ ReturnCode rfalIso15693VICCDecode(const uint8_t *inBuf,
     *outBufPos = 0;

     /* first check for valid SOF. Since it starts with 3 unmodulated pulses it is 0x17. */
-    if ((inBuf[0] & 0x1fU) != 0x17U)
+    if ((inBuf[0] & 0x1fU) != 0x17U) // what is received here?
     {
                ISO_15693_DEBUG("0x%x\n", iso15693PhyBitBuffer[0]);
                return RFAL_ERR_FRAMING;
diff --git a/Projects/STM32L476RG-Nucleo/Applications/X-NUCLEO-NFC06A1/ndef_rw/Src/analogConfigTbl_NFC06A1.c b/Projects/STM32L476RG-Nucleo/Applications/X-NUCLEO-NFC06A1/ndef_rw/Src/analogConfigTbl_NFC06A1.c
index bccb9657..9354cf31 100755
--- a/Projects/STM32L476RG-Nucleo/Applications/X-NUCLEO-NFC06A1/ndef_rw/Src/analogConfigTbl_NFC06A1.c
+++ b/Projects/STM32L476RG-Nucleo/Applications/X-NUCLEO-NFC06A1/ndef_rw/Src/analogConfigTbl_NFC06A1.c
@@ -437,13 +437,13 @@ const uint8_t rfalAnalogConfigCustomSettings[] = {

     /* Mode Name: POLL_V_COMMON_RX, Mode ID: 0x1002 */
     MODE_ENTRY_7_REG(0x1002,
         0x000a,0x04,0x00, /* Receiver Operation Selection (dis_corr) : Correlation operation ; Use Correlator Receiver */
         0x000b,0xff,0x13, /* User Defined */
-        0x000c,0xff,0x2d, /* User Defined */
+        0x000c,0xff,0xed, /* switch to IQ demodulator - potentially better noise resistance */
         0x000d,0xff,0x00, /* User Defined */
-        0x000e,0xff,0x00, /* User Defined */
+        0x000e,0xff,0x22, /* Increase gain reduction a bit, can also play with higher values */
         0x004c,0xff,0x13, /* User Defined */
         0x004d,0xff,0x01  /* User Defined */
     ),

     /* Mode Name: POLL_AP2P_COMMON_RX, Mode ID: 0x0802 */

Line numbers may not apply 1:1 for your code but the locations should be easily identifiable.

BR, Ulysses