[Bug] NMEA Protocol doesn't keep stats

[dronesalot]

Describe the bug

When PX4 is connected to a NMEA GPS unit (UM980 in my case) the GPS status reports a rate of 0 B/s and an update rate of 0hz.

Typical output shown above.

To Reproduce

connect a NMEA GPS to a serial port and configure it as a GPS.

Run gps status and examine the results:
Connect the drone to a NEMA GPS. Run gps status.

nsh> gps status

INFO  [gps] Main GPS
INFO  [gps] protocol: NMEA
INFO  [gps] status: OK, port: /dev/ttyS5, baudrate: 921600
INFO  [gps] sat info: enabled
INFO  [gps] rate reading:              0 B/s
INFO  [gps] rate position:           0.00 Hz
INFO  [gps] rate velocity:           0.00 Hz
INFO  [gps] rate publication:          0.00 Hz
INFO  [gps] rate RTCM injection:      0.00 Hz
 sensor_gps
    timestamp: 1166797117 (0.077381 seconds ago)
    timestamp_sample: 0

Expected behavior

I have already developed a patch, although I have identified some additional issues with the GPS code, This is the result from the patched code.

nsh> gps status
INFO  [gps] Main GPS
INFO  [gps] protocol: NMEA
INFO  [gps] status: OK, port: /dev/ttyS5, baudrate: 921600
INFO  [gps] sat info: enabled
INFO  [gps] rate reading:           3299 B/s
INFO  [gps] rate position:           5.00 Hz
INFO  [gps] rate velocity:           2.00 Hz
INFO  [gps] rate publication:          6.79 Hz
INFO  [gps] rate RTCM injection:      0.00 Hz
 sensor_gps
    timestamp: 34211212 (0.029154 seconds ago)

I haven't yet figured out how to submit a patch, but this issue is fixed with the following:

diff --git a/src/drivers/gps/gps.cpp b/src/drivers/gps/gps.cpp
index dff88ecbdc..9a6825f95b 100644
--- a/src/drivers/gps/gps.cpp
+++ b/src/drivers/gps/gps.cpp
@@ -475,6 +475,9 @@ int GPS::pollOrRead(uint8_t *buf, size_t buf_length, int timeout)
 
        if (_interface == GPSHelper::Interface::UART) {
                ret = _uart.readAtLeast(buf, buf_length, math::min(character_count, buf_length), timeout_adjusted);
+               if (ret > 0) {
+                       _num_bytes_read += ret;
+               }
 
 // SPI is only supported on LInux
 #if defined(__PX4_LINUX)

diff --git a/src/nmea.cpp b/src/nmea.cpp
index a330c9a..3941bd5 100644
--- a/src/nmea.cpp
+++ b/src/nmea.cpp
@@ -853,13 +853,19 @@ int GPSDriverNMEA::handleMessage(int len)
                _gps_position->satellites_used = MAX(_sat_num_gns, _sat_num_gsv);
        }
 
-       if (_VEL_received && _POS_received) {
+       /** update the stats for the velocity. */
+       if (_VEL_received) {
+               ret = 1;
+               _VEL_received = false;
+               _rate_count_vel++;
+       }
+
+       /** update the stats for the velocity. lat/long is considered to be a gps position update whereas velocity may not be */
+       if (_POS_received) {
                ret = 1;
                _gps_position->timestamp_time_relative = (int32_t)(_last_timestamp_time - _gps_position->timestamp);
                _clock_set = false;
-               _VEL_received = false;
                _POS_received = false;
-               _rate_count_vel++;
                _rate_count_lat_lon++;
        }
 

Screenshot / Media

No response

Flight Log

No response

Software Version

I'm running PX4 v 1.15.1 on a CubePilot Orange

Flight controller

No response

Vehicle type

Multicopter

How are the different components wired up (including port information)

No response

Additional context

No response

[DronecodeBot]

This issue has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/um982-isnt-providing-heading-data/35195/24