Video Mux Routing

The Chameleon v3 has two HDMI and two DisplayPort connectors. The video signals for each of these connectors can be routed through a sequence of demuxes and muxes to connect the port to the FPGA's Multi-Gigabit Transceivers (MGTs) or to an IT68051 HDMI receiver. Note that the DisplayPort signals pass through an MCDP2900 DisplayPort to HDMI converter if they are being routed to the IT68051 HDMI receiver.

The signal routing from connector to FPGA and HDMI receiver can be seen in this diagram. The control signals for the demuxes and muxes are shown by each demux/mux.

Video Mux Routing

Note that the ports are numbered externally as ports 1 and 2 (with HDMI1 and DP1 being closest to the USB-C connectors), but that the routing to the IT68051 receiver is HDMI1/DP1 to port 1, while HDMI2/DP2 are routed to port 0.

The table below shows the routing for DP1 and DP2, with the reference designators for the muxes and demuxes shown in the same order. For example, to route DP1 to the IT68051, set the select line on U3 (which is DP1_PS8468_SW) to 0, set the select line on U18 (which is GP213_IT68051P1_CH_SEL) to 0, and don't bother with the select line on U11.

U3/U22      U18/U31     U11/U14     DP1/DP2 connection
------      -------     -------     ------------------
0           0           x           IT68051
1           x           0           FPGA

This table shows the routing for HDMI1 and HDMI2, with the reference designators for the demuxes and muxes shown in the same order. For example, to route HDMI2 to the FPGA, set the select line on U29 (which is HDMI2_GP213_CH_SEL) to 1, don't bother with U31, and set the select line on U14 (which is SOMP2_MODE_SEL) to 1.

U10/U29     U18/U31     U11/U14     HDMI1/HDMI2 connection
------      -------     -------     ----------------------
0           1           x           IT68051
1           x           1           FPGA

Note that U3 and U22 play no part in the HDMI signal routing, while U10 and U29 play no part in the DisplayPort signal routing.

Only one of HDMI1 and DP1 can be connected to the FPGA. The other can be connected to the IT68051, or it can be left unconnected. The same restriction applies to HDMI2 and DP2.

Shell Commands

The videomux shell command offers a way to read and set the state of the muxes and demuxes. videomux get will read the select signals for all 8 of the chips that involved in demuxing and muxing the signals and report them as raw 0 and 1. It will then interpret those signals to show the routing for the DisplayPort and HDMI connections to the HDMI receiver and the FPGA MGTs:

$ videomux get
U3:0 U10:1 U11:1 U18:0 U22:0 U29:1 U31:0 U14:1
DP1: HDMI RX
DP2: HDMI RX
HDMI1: FPGA
HDMI2: FPGA

To set the muxes and demuxes, use the videomux command, specify the port as dp1, dp2, hdmi1, or hdmi2, and the destination of fpga or rx (the IT68051 HDMI receiver). So, for example:

$ videomux dp1 fpga
Connect DP1 to FPGA
$ videomux get
U3:1 U10:1 U11:0 U18:0 U22:0 U29:1 U31:0 U14:1
DP1: FPGA
DP2: HDMI RX
HDMI1: n/c
HDMI2: FPGA

DisplayPort to IT68051

The Proto 0 board can connect either DisplayPort connector to the IT68051 HDMI receiver IC. By default, DP2 is enabled.

Connect a USB-C DisplayPort adapter to a Chromebook

USB-C DisplayPort adapter

Connect the DisplayPort cable to DP2 (furthest from the USB-C connectors)

DisplayPort cable connected to DP2

The Chromebook will recognizes an external display named “ITE6802” with various resolutions available up to 4K.

ITE6802 Monitor

To switch to the other DisplayPort, type the following commands in the EC shell:

videomux dp1 rx
it68051 select 1
it68051 hpd 1 1

To switch back to DisplayPort 2, type the following commands:

videomux dp1 rx
it68051 select 0
it68051 hpd 0 1

Note: The IT68051 numbers its ports 0 and 1, while the DisplayPort connectors are numbered 1 and 2. DP1 connects to the IT68051‘s port 1, and DP2 connects to the IT68051’s port 0.

To hold the IT68051 in reset (disabling the external display),

io set IT68051_RST_L 0

To release reset and re-initialize the IT68051,

io set IT68051_RST_L 1
it68051 init