Product guide

Description
XAPP1178 (v2.0) January 23, 2015 www.xilinx.com 12
DPCD reads/writes:
• AUX reads/writes to DPCD: Using AUX transactions, a DPTX device can read a DPRX
DisplayPort Configuration Data (DPCD). Each DPRX device has a 20-bit address space that
the 8-bit DPCD registers are mapped to. The DPCD contains registers that allow a DPRX to
declare its capabilities and status, and allows a DPTX device to control and configure the
DPRX.
• I2C-over-AUX: A DPTX can also determine a sink device display identity and capabilities.
This information is located in a sink Extended Display Identification Data (EDID) that can be
accessed using the I2C protocol. The DPRX communicates with the sink by mapping I2C
transactions to AUX ones.
• MST sideband messages: Sideband messages are mapped to AUX transactions by the SW
driver. This allows the DPTX to access remote DPRX devices in an MST topology.
Link Policy Maker
The SW driver implements the link policy maker (LPM). When run, the LPM algorithm will train
the main link connecting a DPTX with a DPRX. Upon successful link training, stream data can be
sent over the main link.
The driver attempts to train the link based on the configured link rate and lane count set in the
user application.
The link training process consists of two sequences:
• The clock recovery sequence: where the clocks are recovered and PLLs are locked.
• The channel equalization sequence: where all lanes achieve channel equalization, symbol
locked, and interlane alignment.
The status of running these sequences are checked on all the lanes by the SW driver using AUX
reads from the DPRX DPCD.
If "adaptive training" is enabled, the implementation of the LPM algorithm in the driver will
downshift — first the lane count, then the link rate. If training fails on the requested link rate
and lane count configuration, it will attempt to train at a reduced lane count and link rate
configuration.
Stream Policy Maker
The stream policy maker calculates the necessary values to configure the main stream
attributes (MSA) and controls the symbol mapping of the video data to be sent.
Each of the calculations is done independently per stream. In SST mode, the first stream should
be used as the Stream argument when using the SPM functions.
The SW driver writes the calculations to the DPTX core registers in order to program
transmission of stream data over the main link.