nRF9160 with m4 MCU, camera, and LCD screen project

Reporting back on progress here, am beginning to use the Feather nRF9160 in the development platform so I went to program it and tried many times with the bootloader.

Not knowing if it was a pin routing issue or some other issue I tried quite a few different pin mapping combinations (for UART2) but could not get any response after loading with the bootloader.

Of course I didn’t notice the fine print “IMPORTANT: updates above _192kB will not work with the current version of the bootloader. Examples like the asset_tracker require a programmer.” on the page
https://docs.jaredwolff.com/nrf9160-programming-and-debugging.html

It appears the program I am attempting to load, serial lte modem, is about 202Kb in side, just above that limit. Pulled out the nRF9160DK and loaded it with nrfjprog, but in doing so I wiped out the bootloader (oops). I will try to recover it later, but the good news is I got the pin layout fixed for UART2 so I would like to report some things about it.

I am using the following two pins for UART2 communication and here is the routing that I discovered.
The GPIO numbers appear to refer to the actual GPIO numbers on the MCU, so P0.03 is 3, etc, and it appears to be a little different than the silkscreen numbers.

Here is the pin mapping from the overlay file (circuitdojo_feather_nrf9160ns.overlay):

&uart1 {
	status = "okay";

	current-speed = <115200>;
	tx-pin = <0>;
	rx-pin = <2>;
};

&uart2 {
	compatible = "nordic,nrf-uarte";
	//current-speed = <921600>;
	current-speed = <115200>;
	// for CTS  RTS support
	/*
	tx-pin = <4>;
	rx-pin = <2>;
	rts-pin = <3>;
	cts-pin = <0>;
	hw-flow-control;
	*/

	// without CTS RTS support
	tx-pin = <3>; // Feather nRF9160 D7 (as marked on the silkscreen)
	rx-pin = <1>; // Feather nRF9160 D5 (as marked on the silkscreen)
};

This appears to follow the Actinius Icarus, however I never was able to find the schematics for the Icarus. Something that I would like to have if anyone knows where to get them. I can’t find it on their website, is it buried?

Anyway, this time around I ran into those two issues, one with the pin mapping, and the other with the bootloader loading. It appeared to load correctly but did not do anything when reset. For reference here are the two commands I used, one for the bootlaoder, the other for nrfjprog, for reference.

I am also going to attach the two bin files here for you to look at. You should receive serial output on the two pins D5 and D7 upon powerup/reset, nothing will come through the USB connection. Baud rate is 115200.

/opt/nordic/newtmgr conn add serial type=serial connstring=‘dev=/dev/tty.SLAB_USBtoUART,baud=1000000’
/opt/nordic/newtmgr -c serial image upload build/zephyr/app_update.bin

/usr/local/bin/nrfjprog -f NRF91 –program build/zephyr/merged.hex –sectorerase

The compiled project, and all related is here, nRF SDK version 1.4.99-dev1.
https://www.drassal.net/filestore/serial_lte_modem_circuitdojo_feather_nrf9160_20210128.zip
(Still can’t get a file to upload, dragging it into here just copies the text of the filename it seems)
If you would like to look, see if you can get the file build/zephyr/app_update.bin to work with the bootloader. Confirmed mixed.bin works with nrfjprog. No rush on this though, since I have a work around now with nrfjprog.

Next bump I ran into.
I wanted to power the nRF9160 from one of the header pins, I don’t want to push 3V3 through the 3V3 pin since I am not sure the Feather M0 that I am using can handle the load of the nRF9160. What I wanted to do is tie the two “USB” pins together, and I noticed there is a diode that prevents powering FROM the USB pin, from the direction of the diode it only OUTPUTS the USB power from the nRF9160’s USB connector to the USB pin on the header.

Note, USB pin refers to JP2 pin 3, 5V0 tagged on the schematic.

What I resorted to is using a micro USB connector and plugging it in, this connector is connected to the “USB” pins on the Feather M0 to power the Feather nRF9150’s 3V3 regulator.

Not sure if it is a good idea to remove that diode, or maybe provide a couple pads on the bottom to solder bridge to bypass the diode if someone wants to backfeed power into the “USB” pin on the header to provide power to the Feather nRF9160’s 3V3 regulator.

Correct me if I am wrong here, but it appears the only way to power the Feather nRF9160’s 3V3 regulator is through the micro USB connector (or battery connector). I don’t dare feed 5V0 into that battery connector, I don’t think the charging IC will be happy with me.

One more note, the “enable” pin, JP2 pin 2, also can’t be tied to the Feather M0, it might be opposite to the function of the M0’s enable pin. It appears to cut power, I didn’t really investigate this, I just removed the connection from the Feather nRF9160 to the Feather M0 on the “enable” pin.

More and more I am isolating more pins, might just be better to fully isolate the two boards and only connect the needed power, reset, and UART pins…

If it is not apparent already, I am using one of the Feather Tripler boards…
https://www.adafruit.com/product/3417