Why does rfalST25xVPollerWritePassword() fail on ST25TV02KC?

[MERSI]

Hi everyone,

I'm working on writing the configuration password (PWD_CFG, 0x00) to an ST25TV02KC NFC tag using the ST25R3916B reader and the RFAL middleware (X-CUBE-NFC6). I am following the standard procedure:

1. Open a CONFIG security session using PresentPassword (XORed Password)

2. Generate a new XOR-coded password using GetRandomNumber

3. Call WritePassword to write a new password (in this case, still 0x00..0x00 for testing)

Here's the code I use:

  if (generateXorPassword(uid, pwd_cfg, xorPwd) != RFAL_ERR_NONE) goto ERROR_RED_LED;
    if (rfalST25xVPollerPresentPassword( // 0x00 = PWD_CFG
            RFAL_NFCV_REQ_FLAG_DEFAULT | RFAL_NFCV_REQ_FLAG_ADDRESS,
            uid,
			0x00,  // PWD_CFG
            xorPwd, sizeof(xorPwd)
        ) != RFAL_ERR_NONE)
    {
        goto ERROR_RED_LED;
    }
    // CONFIG Security Session is now open!

    {
    	// Change PWD_CFG (0x00) 
        if (generateXorPassword(uid, pwd_cfg, xorPwd) != RFAL_ERR_NONE) goto ERROR_RED_LED;
    	if(rfalST25xVPollerWritePassword(
    		RFAL_NFCV_REQ_FLAG_DEFAULT | RFAL_NFCV_REQ_FLAG_ADDRESS,
    	    uid,
    	    0x00,              // PWD_CFG
			xorPwd,
    	    4
    	) != RFAL_ERR_NONE) goto ERROR_RED_LED;
    }

Despite the session being open, the WritePassword() command always fails (with return code 5, RFAL_ERR_REQUEST).
The PresentPassword() call succeeds, and I can confirm that the session is active.

What could be the reason that WritePassword() is failing?

Any help or ideas would be greatly appreciated!

Thanks in advance.

[Brian TIDAL]

Hi,

set a breakpoint in rfalNfcvParseError. What is the err value in rfalNfcvParseError when the WritePassword fails? See WritePassword error codes in the datasheet.

As a side comment, RFAL_NFCV_REQ_FLAG_ADDRESS is automatically set when the uid parameter is non-null in the various APIs. Thus, it is not needed to set it on user side.

Rgds

BT

[MERSI · Accepted solution]

@Brian TIDAL Thank you

It is 12h (Security Session is closed). But I just opened the security session on line above (returns no error) .

I've found the problem. In the generateXORPassword I am calling GetRandomNumber. This function deactivates also the rf field for a while. This ends the security session and therefore I could not write a new password. I am calling the random number by my own and now it works.