Implement a developer UART on the USB AUX lines

[dapec_2892156]

• We have a developer serial port (UART) which we typically bring out to a connector on our board and connect to a PC for debug messages.
• The UART needs to be available early in the boot process to see kernel boot messages.
• I only need the Rx and Tx UART pins, not a full function UART.
• I wanted to find a way to make use of the USB Type-C connector to bring out this UART for a developer.
• We plan to implement the CCG4M chip with the Display Port, but the UART would be the default function over the DisplayPort.

I'd like to implement this with as little hardware as possible. Can I connect the UART to one of the CCG4M's open Serial Communication Blocks (SCB) and have it routed inside the chip to the SB1 and SB2 output pins?

Is there any conflict on the USB bus with having our data communication on the SB1 and SB2 pins of the connector?

Is there another scheme you suggest to achieve this that would not interfere with regular USB 3.1 data or CC pin communications?

[ShifangZ_26]

Hi David,

What's you are going to implements on SBU1 and SBU2 with DisplayPort Alt Mode on Type-C is conflict with the Alt mode SPEC. Since SBU1 and SBU2 is AUX_N and AUX_P when Type-C port is transmit DisplayPort signals.

The way I can thought about your questions is you could only transmit 2 lane DisplayPort signals and then re-use the SS USB signals pins working as UART. Or use the B6/B7 of Type-C plug for UART, since for Type-C plug， there are no B6/B7 same as Type-C receptacle for D+/D-. You could still wire out for debugging.

Best Regards,

Lisa

[dapec_2892156]

I would not use UART and the DisplayPort functionality at the same time. Would there still be a conflict?

If I connect B6/B7 pins, then I lose the ability to plug in a USB cable in either orientation.

[OlEr_1999891 · Accepted solution]

Hi!

We have enabled a USB HID device in the CCG3/4 based on the source code provided in the EZ-PD™ CCG3 USB Type-C to DisplayPort Cable Solution | Cypress Semiconductor  reference implementation which is enabled via the D+/D- on IC so that you can use to publish your debugging messages. Not sure you can enable an UART block on the CCG4, you would need to lots of coding yourself since it is hard to port the standard PSoC components to CCGx.

Then you could maybe but a simple 2-channel mux in front of the receptacle to mux either SBU or D+/D- onto the SBU pins and controll it using a free GPIO on the CCG4M. Not very beautiful and you would get HID instead of UART. The mux is cheap though.

Cheers

Olof

[ShifangZ_26]

Hi David,

1. If you do not use UART and dispalyPort at same time, may be you could have a try. I am not sure whether if it is side-effect on AUX channel have a node on it.

2. The B6/B7 is not pinout for Type-C plug and Type-C connector have such pins on it. For Type-C plug, the orientation is fixed. There are only CC and VCONN.

Best Regards,

Lisa 

[dapec_2892156]

2. The B6/B7 is not pinout for Type-C plug and Type-C connector have such pins on it. For Type-C plug, the orientation is fixed. There are only CC and VCONN.

lisz See below from "CCG EVK Base Board Schematic.pdf". My application is as a Dual Role device.

[ShifangZ_26]

Hi David,

The schematic you showed is Type-C receptacle design. If you have chance to take a look the Type-C plug define, you will knew the slightly difference.

Best Regards,

Lisa