ST STM32G4 Series Reference Manual page 2012

USB Type-C™ / USB Power Delivery interface (UCPD)
Transmitter behaviour in the case of errors
The under-run condition (TXUND interrupt) may happen by accident and in this case, the
UCPD will be starved of (the correct) Tx payload and will not be able to complete the Tx
message correctly. This is a serious error (for this to happen the software will have failed to
respond in time). As a result the hardware will ensure the CRC is incorrect at the end of the
message, thus guaranteeing the message to be discarded at the receiver.
45.4.5 UCPD BMC Receiver
The UCPD BMC receiver is responsible for these primary functions:
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The receiver is activated as soon as the UCPD is enabled (via UCPDEN), but is inactive
during all periods of transmit. At the moment of the enable, in order to start cleanly, it will
initially wait for an IDLE line state before attempting to receive a message.
UCPD Receiver high level architecture is shown in
2012/2083
Preamble detection / timing derivation
BMC decoding
4b5b decoding
K-Code ordered set recognition (3 of 4 correct basis)
CRC checking
SOP detection
EOP detection (should be always active even ahead of normal behavior due to
Hard Reset characteristics)
Figure
RM0440 Rev 1
682:
RM0440