RM0440 Rev 4 2053/2126
RM0440 USB Type-C™ / USB Power Delivery interface (UCPD)
2079
Figure 682. UCPD BMC transmitter architecture
BMC encoder
The bi-phase mark coding method is defined in the IEC 60958-1 Digital Audio Interface
Part:1 General Edition 3.0 2008-09 www.iec.ch specification.
The half-bit clock hbit_clk is derived from ucpd_clk through a simple divider controlled by the
HBITCLKDIV[5:0] bitfield of the UCPD_CFGR1 register. This ensures the same duration of
high and low half-bit periods (if neglecting a small difference due to different rising and
falling edge duration and due to jitter), and the same bit duration (if neglecting jitter).
Transmitter timing and collision avoidance
Hardware support of collision avoidance is made as a function of the half bit time for the
transmitter. Two counters are implemented:
– tInterFrameGap: via IFRGAP (pre-defined value, can be altered)
– tTransitionWindow: via TRANSWIN
(pre-defined value, can be altered)
These two counters once set correctly generates the interframe gap.
Hard Reset in transmitter
In order to facilitate generation of a Hard Reset, a special code of TXMODE field is used. No
other fields need to be written.
On writing the correct code, the hardware forces Hard Reset Tx under the correct (optimal)
timings with respect to an on-going Tx message, which (if still in progress) is cleanly
terminated by truncating the current sequence and directly appending an EOP K-code
sequence. No specific interrupt is generated relating to this truncation event.
Transmitter behavior in the case of errors
The under-run condition (TXUND interrupt) may happen by accident and in this case, the
UCPD is starved of (the correct) Tx payload and is not able to complete the Tx message
correctly. This is a serious error (for this to happen the software fails to respond in time). As
a result the hardware ensures the CRC is incorrect at the end of the message, thus
guaranteeing the message to be discarded at the receiver.
MSv45544V2
CRC
USB PD
transmitter
state machine
4b5b
encode
UCPD_TXDR
UCPD_TX_ORDSET
UCPD_CR
UCPD_TX_PAYSZ
Tx message
contents
Tx message
control
BMC
encode
UCPD_CFG1
UCPD_CFG2
UCPD_CFG3
Message
parameters
Message
control
General
configuration
ucpd_pclk
clock domain
Fixed
framing
To analog
PHY
ucpd_clk
clock domain
hbit_clk
clock domain
Message
data
Message
data
Configuration of
the peripheral
Registers
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