RTT works but Serial doesnt

[bem22]

As the title says, I'm struggling to make the serial interface work with nRF5240 CKAA

I'm using nRF52840DK for flashing the chip by using the P20 header to power and connect to the target (3V0, SWD CLK, SWD IO) and GND from outside the header.

As said, RTT connects by itself when automatically searching for it, but Serial communication doesn't work and I am not sure if  my settings are to blame.

I am using the 52840DK config to which I added this prj.conf

# Logger module
CONFIG_LOG=y

# Button and LED library
CONFIG_DK_LIBRARY=y

CONFIG_I2C=y

# Bluetooth LE
CONFIG_BT=y
# STEP 1 - Include the Peripheral Role support

CONFIG_BT_PERIPHERAL=y

# STEP 2 - Change the Bluetooth LE device name to Nordic_Peripheral
CONFIG_BT_DEVICE_NAME="TEST_UNIT_4"

# Increase stack size for the main thread and System Workqueue
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048
CONFIG_MAIN_STACK_SIZE=2048

CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=n
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y

CONFIG_BOARD_ENABLE_DCDC=n

What am I missing?

[bem22]

That would be awesome. I am not using the Reset pin and the p1.00 for anything really. 

For nRF5240 CKAA I am using, the Reset is K6 (P0.18) and P1.00/TraceData0 is J3

So you think it's worthwhile attempting to switch those in software to perform as UART?

If so, where should I connect them on the DK and will the UART to USB interface listen to the target's UART by itself?

Also one more question, can you explain how RTT works? I assume it uses SWDIO and SWDCLK - what kind of protocol is it and is it parallel to UART?

Thanks a lot for your support!

[Jørgen Holmefjord]

bem22 said:

So you think it's worthwhile attempting to switch those in software to perform as UART?

Yes, this should be simple to achieve. Create an overlay file where you configure the UART pins to P0.18 and P1.00. Make sure that CONFIG_GPIO_AS_PINRESET=n is set in the prj.conf file. Note that you need to do an eraseall operation (nrfjprog --eraseall) on the chip to disable the pinreset if it has been enabled by a previously programmed firmware.

bem22 said:

If so, where should I connect them on the DK and will the UART to USB interface listen to the target's UART by itself?

Yes, you need to connect the configured UART pins on the external board to the UART pins on the DK (TX=P0.06, RX=P0.08). Also make sure that you erase any firmware present on the nRF52 chip on the DK (disconnect debug pins from external board and run "nrfjprog --eraseall").

bem22 said:

Also one more question, can you explain how RTT works? I assume it uses SWDIO and SWDCLK - what kind of protocol is it and is it parallel to UART?

Real Time Transfer (RTT) is a technology provided by SEGGER. It uses the SWD interface to read/write data from a RAM buffer on the chip. RTT works separately from UART and is only available through the debug interface (SWD).

[bem22]

Thanks a lot, this was very useful.

I tried googling around and also used GPT but couldn't figure out the actual way to set the pins.

It seems like `rx-pin` and `tx-pin` are deprecated ways to setting the pins. 

I read through the pin ctrl api but couldn't translate this to usable prj.cfg 

I also tried to use the device tree interface to set the p0.18 and p1.00 as TX and RX with this result

However, this doesn't allow me to change the default baud rate and add other options because groups can only be used for default nodes.

Also, although I added CONFIG_GPIO_AS_PINRESET=n after eraseall operation and flashed again, I still get this message about pin reset whenever I flash. Is this related?

So far I do not get any message back from UART. Is there anything else I have to enable?

My full prj.cfg is this

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048
CONFIG_MAIN_STACK_SIZE=2048

CONFIG_HEAP_MEM_POOL_SIZE=1024
CONFIG_MINIMAL_LIBC_MALLOC_ARENA_SIZE=2048

CONFIG_BT=y
CONFIG_BT_DEBUG_LOG=y
CONFIG_BT_SMP=y
CONFIG_BT_PERIPHERAL=y
CONFIG_BT_DIS=y
CONFIG_BT_BAS=y
CONFIG_BT_DEVICE_NAME="Panorama Pipette"

CONFIG_BT_SETTINGS=y
CONFIG_FLASH=y
CONFIG_FLASH_PAGE_LAYOUT=y
CONFIG_FLASH_MAP=y
CONFIG_NVS=y
CONFIG_SETTINGS=y

CONFIG_GPIO=y

# I2C Module
CONFIG_I2C=y

# Logger module
CONFIG_LOG=y


CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=n
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y

# Disable DCDC regulator (DK property)
CONFIG_BOARD_ENABLE_DCDC=n

CONFIG_CONSOLE=y
CONFIG_SERIAL=y
CONFIG_UART_CONSOLE=y
CONFIG_UART_INTERRUPT_DRIVEN=y

CONFIG_GPIO_AS_PINRESET=n

[Sigurd]

Hi,

Try

		group1 {
			psels = <NRF_PSEL(UART_TX, 0, 18)>,
				<NRF_PSEL(UART_RTS, 0, 5)>;
		};
		group2 {
			psels = <NRF_PSEL(UART_RX, 1, 0)>,
				<NRF_PSEL(UART_CTS, 0, 7)>;
			bias-pull-up;
		};

If you are having issues with pin reset being enabled when flashing with west, 

try to add board_runner_args(nrfjprog "--softreset") to the board.cmake file, and see if that helps. Ref:

 RE: Disable pin reset for west flash 

https://github.com/nrfconnect/sdk-zephyr/blob/main/boards/arm/nrf52840dk_nrf52840/board.cmake

[bem22]

Thanks for the feedback. I was able to disable the pin reset with your method.

This did the trick.

The default baud rate seems to be 115200

I would like to change that through the prj.conf however the uart0_default settings doesn't allow for other members besides group1 and group2

I will search for alternate ways to doing this now the pin reset is off.

Many thanks again