GNSS callbacks don't fire (gnss sample)

[ASerbinski]

Describe the bug
I'm working with an Adafruit Feather M0 Lora (https://docs.zephyrproject.org/latest/boards/adafruit/feather_m0_lora/doc/index.html) with a GPS "featherwing" (https://www.adafruit.com/product/3133)

Currently attempting to get the GNSS sample working correctly (https://github.com/zephyrproject-rtos/zephyr/tree/main/samples/drivers/gnss)

Now because the GPS uses the same UART as is normally used for the Zephyr console, I had to make some changes to put the console on the USB in addition to defining the GNSS.

I added these lines to prj.conf;

CONFIG_USB_DEVICE_STACK=y
CONFIG_USB_DEVICE_PRODUCT="Feather M0 Lora w/GPS"
CONFIG_USB_DEVICE_PID=0x0004
CONFIG_USB_DEVICE_INITIALIZE_AT_BOOT=y

And I created boards/adafruit_feather_m0_lora.overlay:

/ {
	chosen {
		zephyr,console = &cdc_acm_uart0;
		zephyr,shell-uart = &cdc_acm_uart0;
	};

	aliases {
		gnss = &sercom0;
	};
};

&sercom0 {
	current-speed = <9600>;
	gnss: gnss-nmea-generic {
		compatible = "gnss-nmea-generic";
	};
};

&usb0 {
	cdc_acm_uart0: cdc_acm_uart0 {
		compatible = "zephyr,cdc-acm-uart";
	};
};

It builds fine, it flashes fine, and I can receive from the console using minicom, which gives me lots of output that looks like this (I've truncated some lines due to sensitive location data);

[00:00:00.000,000] <dbg> modem_chat: modem_chat_script_start: running script: gnss_nmea_generic_init_chat_script
[00:00:00.000,000] <dbg> modem_chat: modem_chat_script_stop: gnss_nmea_generic_init_chat_script: complete
*** Booting Zephyr OS build v3.6.0-4165-g5f1e1c7b34ae ***
[00:00:00.063,000] <dbg> modem_chat: modem_chat_on_unknown_command_received: )�R��j
                                                                                   $GLGSA,.....
[00:00:00.146,000] <dbg> modem_chat: modem_chat_log_received_command: $GNRMC,.....
[00:00:00.188,000] <dbg> modem_chat: modem_chat_on_unknown_command_received: $GNVTG,.....
[00:00:00.960,000] <dbg> modem_chat: modem_chat_log_received_command: $GNGGA,.....
[00:00:01.022,000] <dbg> modem_chat: modem_chat_on_unknown_command_received: $GPGSA,.....
[00:00:01.064,000] <[00:00:01.148,000] <dbg> modem_chat: modem_chat_log_received_command: $GNRMC,.....
gnss-nmea-generic: gnss_info: {satellites_cnt: 7, hdop: 1.400, fix_status: GNSS_FIX, fix_quality: GNSS_SPS}
gnss-nmea-generic: navigation_data: {latitude: xxxxx, longitude : xxxxx, bearing xxxxx, speed xxxxx, altitude: xxxxx}
gnss-nmea-generic: gnss_time: {hour: 16, minute: 56, millisecond 55000, month_day 17, month: 5, century_year: 24}
[00:00:01.189,000] <dbg> modem_chat: modem_chat_on_unknown_command_received: $GNVTG,.....

That looks pretty nice, its obviously receiving and processing the data received from the GPS. However, missing is the output from the two callbacks "gnss_data_cb" and "gnss_satellites_cb". These callbacks are apparently not firing, which means that I don't have any way to access the data, which is the actual objective.

Is there a bug here? Or am I missing something?

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[bjarki-trackunit]

Hi, the gnss alias needs to point to the gnss node, rather than the uart node :) The sample contained some overlays which incorrectly pointed to the uart node, which where fixed with this PR #72249

[bjarki-trackunit]

The reason the node needs to be updated is this:

zephyr/include/zephyr/drivers/gnss.h

Lines 454 to 469 in 7046c90

	/**
	* @brief Register a callback structure for GNSS data published
	*
	* @param _dev Device pointer
	* @param _callback The callback function
	*/
	#if CONFIG_GNSS
	#define GNSS_DATA_CALLBACK_DEFINE(_dev, _callback) \
	static const STRUCT_SECTION_ITERABLE(gnss_data_callback, \
	_gnss_data_callback__##_callback) = { \
	.dev = _dev, \
	.callback = _callback, \
	}
	#else
	#define GNSS_DATA_CALLBACK_DEFINE(_dev, _callback)
	#endif

When defining the callback, a pointer to a specific GNSS can be used to filter out which device calls that specific callback, which can be useful if there are two GNSS devices. Setting the _dev argument to NULL would allow the callback to call, but if you tried to use the GNSS API with the UART node (currently pointed to by the alias), you would get undefined behavior :)

[bjarki-trackunit]

Proof that the GNSS callback works is here

zephyr/drivers/gnss/gnss_dump.c

Line 167 in 7046c90

GNSS_DATA_CALLBACK_DEFINE(NULL, gnss_dump_data_to_log);

this is the callback which produces the log output you are seeing :) that was the thing which helped me isolate the issue in the first place (the _dev is NULL)

[ASerbinski]

@bjarki-trackunit ; Thank you so much, I have it working now!