@Eric-Katzfey We've started working again on this project. I've now managed to create a bare bones setup for the apps + sdsp, which piggy packs on the fc_sensor lib.

something like this:

#include <stdio.h>
#include <fc_sensor.h>

void receive_cb(const char *topic,
                 const uint8_t *data,
                 uint32_t length_in_bytes)
{
}
void advertise_cb(const char *topic)
{
}
void add_subscription_cb(const char *topic)
{
}
void remove_subscription_cb(const char *topic)
{
}

int main(int argc, char **argv)
{
    fc_callbacks func_ptr = {
        .rx_callback = &receive_cb,
        .ad_callback = &advertise_cb,
        .sub_callback = &add_subscription_cb,
        .remove_sub_callback = &remove_subscription_cb
    };
    fc_sensor_initialize(false, &func_ptr);
    
    printf("Hello, world!\n");
    return 0;
}

and

#include <main.h>

#define FARF_LOW 1
#include <qurt.h>
#include <HAP_farf.h>

static fc_func_ptrs g_func_ptrs;
// entry point - called by fc_sensor system
int px4muorb_orb_initialize(fc_func_ptrs *func_ptrs, int32_t clock_offset_us)
{
    FARF(LOW, "SLPI Flya Main\n");
    g_func_ptrs = *func_ptrs;

    return 0;
}

int px4muorb_topic_advertised(const char *name)
{
    return 0;
}
int px4muorb_add_subscriber(const char *name)
{
    return 0;
}
int px4muorb_remove_subscriber(const char *name)
{
    return 0;
}
int px4muorb_send_topic_data(const char *name, const uint8_t *data, int data_len_in_bytes)
{
    return 0;
}

And from there I could use the spi functions to read the IMU, so all good.

I was hoping to get some clarification on where does the the proprietary code that interacts with the HW sit? (i.e. sns_flight_controller_sensor). Is it part of libfc_sensor.so? or is it baked in the SLPI firmware found in /home/firmware/slpi.bxx?