The use of BIST receive mode bit in UCPD of STM32G474

[AgoDream]

I don't know the function of the BIST receive mode bits in the picture. According to the description, when this bit is enabled, the protocol layer cannot receive data. So, what does this model do? Please help me resolve this confusion.

Thanks

 

*This post has been translated from Chinese to comply with the ST Community guidelines.

 

 

[ELABI.1]

Hi @AgoDream,

The BIST receive mode is used to test the UCPD functionality without actually receiving the data bytes. It ensures that the CRC checking and GoodCRC message transmission are functioning correctly. It helps in verifying that the UCPD implementation complies with the protocol requirements by ensuring proper handling of BIST packets and synchronization of MessageID.

We have analyzed the situation. When connected to a tester, and upon receipt of a BIST Test Data message, we are required to no longer reply to messages but must still acknowledge them by sending a GoodCRC message. This GoodCRC must include the MessageID 3-bit field that itself will be auto-incremented by the tester. If the RXMODE is set to 1 (BIST receive mode) we will effectively not receive the header or payload via RXDR, but will still get the CRC checks, and an interrupt RXMSGEND. As usual, depending on bit RXERR, we can establish if the CRC was correctly received or not. If RXERR=0 we shall send a GoodCRC Message but using a locally auto-incremented MessageID field. If RXERR=1 we will send no GoodCRC message and do no local auto-increment of our MessageID counter. By this means we should stay in sync despite "guessing" the MessageID via auto-increment. (This bit is a facility, not an obligation)

I hope this clarifies the function and purpose of the BIST receive mode bit.

ELABI.1

 

[AgoDream]

Thank you for replying to my question. I still have a question, what should I fill in the 192 bits data after the message header?

AgoDream

[ELABI.1]

Hi @AgoDream 

For BIST test data, the data should be a sequence of alternating 1s and 0s.

I hope that I have helped you.

Thank you.

ELABI.1