Connecting two GPS on VOXL2

@Eric-Katzfey Thank you for the update. Any quick guide for software configuration which you can suggest for this dual gps setup? My hardware connections would be as follows :

GPS1 on VOXL2 J19 pins 1 to 6 (UART and I2C for GPS and Mag)
GPS2 UART over J18 (Modalai ESC port) and I2C over J19 pins 7 and 8.
I have VOXL2IO also integrated over J19 10,11 and 12 number pins.

By this configuration I can ensure all UART and I2C connections are going to DSP directly.
Here are my queries :

With above mentioned connections I would have to change QUP settings in firmware I guess. Can you mention those places?
Can I follow this link to enable dual GPS as per PX4 mainline or is some other settings would be essential for dual GPS enabling over ModalAI PX4 version?

Eric Katzfey

@Aks Those connections look reasonable. Let me do a little digging to see what would be required to use pins 7 and 8 on J19 for the new magnetometer.

Eric Katzfey

@Aks I looked through the code and I don't see any obvious roadblocks to using pins 7 and 8 on J19 for the second magnetometer. The current magnetometer driver uses -b 1 to specify the i2c bus on pins 4 and 5 of J19. For pins 7 and 8 I think you would need to specify -b 4. I'll try to wire something up and try it on those pins in the next couple of days.

Eric Katzfey

@Aks I hooked up a magnetometer to pins 7 and 8 and it didn't work. But I found the issue in PX4 and was able to get it working by changing a couple of files. Here is the required diff:

voxl-px4-1.12/px4-firmware$ git diff
diff --git a/boards/modalai/rb5-flight/src/board_config.h b/boards/modalai/rb5-flight/src/board_config.h
index d205d7b124..479fb95652 100644
--- a/boards/modalai/rb5-flight/src/board_config.h
+++ b/boards/modalai/rb5-flight/src/board_config.h
@@ -54,7 +54,7 @@
 #define PX4_I2C_BUS_EXPANSION   3  // I2C3: J14 / Power
 #define PX4_I2C_BUS_EXPANSION2  9  // I2C9: J15 / Radio Receiver / Sensors
 
-#define PX4_NUMBER_I2C_BUSES    3
+#define PX4_NUMBER_I2C_BUSES    4
 
 #define PX4_I2C_OBDEV_BMP280  0x76
 
diff --git a/boards/modalai/rb5-flight/src/i2c.cpp b/boards/modalai/rb5-flight/src/i2c.cpp
index ce4b99a20c..49e361a877 100644
--- a/boards/modalai/rb5-flight/src/i2c.cpp
+++ b/boards/modalai/rb5-flight/src/i2c.cpp
@@ -36,6 +36,7 @@
 constexpr px4_i2c_bus_t px4_i2c_buses[I2C_BUS_MAX_BUS_ITEMS] = {
        initI2CBusExternal(1),
        initI2CBusExternal(2),
+       initI2CBusExternal(4),
        initI2CBusInternal(5)
        //initI2CBusExternal(3),
        //initI2CBusExternal(9),

@Eric-Katzfey Thank you for this information. I highly appreciate this. How about using J18 for GPS UART? What changes would be essential for this? Also any idea about EKF configuration for using dual GPS?

Eric Katzfey

@Aks Should be no problem using J18 for GPS instead of ESC.

Eric Katzfey

@Aks We've never done a dual GPS configuration so not sure what is required for PX4.

@Eric-Katzfey All the points noted. Thanks alot for all the detailed digging into this. I would try out this configuration. One point which I missed is, In order to connect GPS to J18 UART, we need to change some port number / QUP number right? If you can clarify this it would be great.

Eric Katzfey

@Aks Unfortunately, there seems to be a bug in the handling of options in the gps driver. The standard uart ports are 2 for the ESC (J18), 6 for the GPS (J19), and 7 for RC (Also on J19). The default port in the gps code is 6. You should be able to pass a different port to the gps driver using the -d option. However, px4_getopt in gps.cpp isn't parsing it if I pass it a different port with the -d option. In fact, you can see that the Holybro gps start line includes -d 7 and -b 115200. The code seems to parse the baudrate fine but not the port which is a good thing because port 7 is for RC, not GPS! Anyways, long story short, in order to put the gps on port 2 you would need to figure out why the gps driver is not parsing the d option correctly first.

@Eric-Katzfey Cool thank you. This gives me some lead to think on. I will debug this further. One small query. Can I run two gps driver with different 'd' options from config file or their can be conflict of same name services running? Just checking for clarity.

Eric Katzfey

@Aks You should be able to run two. But, again, we have never tested.