Implementing SWD over a Type A to C USB cable

RE: Implementing SWD over a Type A to C USB cable

Søren — Sun, 13 Jan 2019 23:39:35 GMT

Just a side node. To void a switch interface the cable connection could act as a switch. That would, in my opinion make a smoother user experience, if only one switch is needed. Compared to opening the shell and pushing some tiny button. One scenario would be, to switch between beacon mode and slave/master mode, set on a timer. To program the nrf52 a SWD to USB-C (DAM) converter would come in handy. From what i gather, the CC1 and CC2 pins must be pulled up with resistor values depending og the case. The only downside, as of now, is the cost. But then again, the project will be futuristic and open. To use the cable-switch approach is likely a smart choice, if the chip is running on a rechargeable power source. Just saying.

RE: Implementing SWD over a Type A to C USB cable

Søren — Sun, 13 Jan 2019 08:32:55 GMT

Which pins to choose for Debug Accessory Mode? Any SWD standard?

The external device test system signals to the target system to enter debug accessory mode via CC1 and CC2 both being pulled down with an Rn resistor value or pulled up as Rp resistor value from the test plug (Rp and Rn specified in Type-C spec).

After entering debug accessory mode, optional orientation detection via the CC1 and CC2 is done via setting CC1 as a pullup of Rd resistance and CC2 pulled to ground via Ra resistance (From the test system type-c plug). While optional, orientation detection is required if you want usb power delivery communication to be functional.

In this mode, all digital circuits are disconnected from the connector, and 14 underlined pins can be used to expose debug related signals (e.g. JTAG interface). USB IF requires for certification that security and privacy consideration and precaution has been taken and that the user has actually requested that debug test mode be performed.

GND	TX1+	TX1−	V_BUS	CC1	D+	D−	SBU1	V_BUS	RX2−	RX2+	GND
GND	RX1+	RX1−	V_BUS	SBU2	D−	D+	CC2	V_BUS	TX2−	TX2+	GND

If you don't care about power delivery communication, but still requires flippability of the type-c cable, your test plug will need to be arrange as below. With CC1 and CC2 both being pulled down with an Rn resistor value or pulled up as Rp resistor value from the test plug.

GND	TS1	TS2	V_BUS	CC1	TS6	TS7	TS5	V_BUS	TS4	TS3	GND
GND	TS3	TS4	V_BUS	TS5	TS7	TS6	CC2	V_BUS	TS2	TS1	GND

This mirroring of test signals will provide you with 7 test signals for your usage instead of 14, but with the benefit of minimising extra parts count for orientation detection.

en.wikipedia.org/.../USB-C

RE: Implementing SWD over a Type A to C USB cable

MartinBL — Mon, 29 Jan 2018 09:52:09 GMT

I think I might have misunderstood your initial post. You can use any of the lines in the plug for any purposes you wish, as long as you meet the connector electrical specification. But if anybody accidentally plugs your type A connector into a computer you might destroy the computer and/or the board - We cannot speculate about this or make any guarantees if you proceed to break the standard.

RE: Implementing SWD over a Type A to C USB cable

Josh — Fri, 26 Jan 2018 17:47:14 GMT

Hi Martin, Yes, I understand that there are no UART lines or SWD dedicated lines in USB cables, I was wondering if I could re-purpose the SS lines for SWD if I am not using SS data. Thanks

RE: Implementing SWD over a Type A to C USB cable

MartinBL — Fri, 26 Jan 2018 11:19:20 GMT

I might still be misunderstanding your intentions, but

There are no UART lines in USB cables. If you want to communicate with an nRF52832 through USB you will have to use some sort of USB to UART converter.
There are no SWD lines in USB cables. To use SWD you will need some sort of MCU to convert USB to SWD.
The USB Vbus voltage is 5V. You cannot power an nRF52832 device with 5V without a voltage converter regulating the voltage down to < 3.6V.

In case you are not aware the nRF52840 has USB and can be powered from Vbus.

RE: Implementing SWD over a Type A to C USB cable

Josh — Thu, 25 Jan 2018 17:23:35 GMT

We will connect to a debugger for debugging purposes, but we want to be able to be plug into a computer directly and still charge for end-user.

RE: Implementing SWD over a Type A to C USB cable

MartinBL — Thu, 25 Jan 2018 12:40:41 GMT

Are you planning to blug the A side of the cable into a computer and connect the pins on the C side directly to the nRF52 with nothing in between?