STSAFE-A110 STSAFEA_COMMUNICATION_ERROR on all reads

[Teedoubleyuh]

Hi,

I ported example projects from en.x-cube-safea1\project\NUCLEO-L476RG for MbedTLS cryptolib for use on my B-U585I-IOT02A Discovery Kit. The STSAFE-A110 is powered correctly and NRESET is pulled high. It never errors on writes to the device, but all reads that execute the StSafeA_Receive function in stsafea_service.c return STSAFEA_COMMUNICATION_ERROR. In fact, it's very specifically always happening here (code snippet below) where after calling StSafeA_ReceiveBytes and getting STSAFE_BUS_OK, it is masking the header value with the inverse of STSAFEA_CMD_HEADER_RMACEN which always turns STSAFE_BUS_OK (0x00) to 0x01 which is STSAFEA_COMMUNICATION_ERROR. Any idea what I could be doing so that I can get past this?
Thanks!

if (status_code != STSAFEA_BUFFER_LENGTH_EXCEEDED)

{

if (status_code == (StSafeA_ResponseCode_t)STSAFEA_BUS_OK)

{

status_code = (StSafeA_ResponseCode_t)(uint8_t)((uint8_t)pTLV_Buffer->Header &

~(uint8_t)STSAFEA_CMD_HEADER_RMACEN); <---- *** this is changing the STSAFEA_BUS_OK (0x00)

to 0x01 which is STSAFEA_COMMUNICATION_ERROR

}

[Jacob WOODRUFF]

Hi All,

This post has been escalated to the ST Online Support Team for additional assistance. We'll contact you directly.

Regards,
Jake

ST Support

[Teedoubleyuh · Accepted solution]

I believe the issue was my CRC_Compute function mapped to StSafeA_HW_Probe. Rather than use the software CRC function produced by x-cube-safea1, I initially tried to map it to the hardware CRC of the STM32U585 I'm using. This wasn't properly handling the header tag that is also included in CRC calculations.

I am still curious though if you can tell me why the CRC_Compute function does a byteswap on the CRC. Is it related to the byte order the payload is transmitted to the STSAFE-A110? I only ask because I compared the CRC results to an online calculator that uses the CRC-16/x-25 algorithm and the online results do not swap the bytes, so for example, the CRC_Compute may give result 0x73CD but the online calculator gives result 0xCD73.

	uint32_t CRC_Compute(uint8_t *pData1, uint16_t Length1, uint8_t *pData2, uint16_t Length2)
	{
	  (void)Length1;
	  uint16_t crc16 = 0;
	  if ((pData1 != NULL) && (pData2 != NULL))
	  {
	    crc16 = StSafeA_Crc16_ccitt(pData1[0], pData2, Length2);
	
	    crc16 = (uint16_t)SWAP2BYTES(crc16);
	    crc16 ^= 0xFFFFU;
	  }
	  return (uint32_t)crc16;
}

[Pavel A.]

> I am still curious though if you can tell me why the CRC_Compute function does a byteswap on the CRC.

Hmm. I don't have STSAFE-A110 but it's kind of tradition for I2C devices to use big endian data format. The MCU itself (and most of the world) is little endian.

[Teedoubleyuh]

Ok, I think I'll just continue to use the CRC_Compute functions generated byte x-cube and not dare to try the hardware CRC. :)
Thanks!