AP_Compass: detect conflict between AK09916 and ICM20948

this detects if we have both a AK09916 and an ICM20948 on the same i2c
bus. If that is found then the ICM20948 is disabled as it otherwise we
will have two devices on the same i2c address

libraries/AP_Compass/AP_Compass_AK09916.cpp

@@ -119,17 +119,52 @@ bool AP_Compass_AK09916::init()
             // not an ICM_WHOAMI
             goto fail;
         }
-        // see if ICM20948 is sleeping
-        if (!dev_icm->read_registers(REG_ICM_PWR_MGMT_1, &rval, 1)) {
+        uint8_t retries = 5;
+        do {
+            // reset then bring sensor out of sleep mode
+            if (!dev_icm->write_register(REG_ICM_PWR_MGMT_1, 0x80)) {
+                goto fail;
+            }
+            hal.scheduler->delay(10);
+
+            if (!dev_icm->write_register(REG_ICM_PWR_MGMT_1, 0x00)) {
+                goto fail;
+            }
+            hal.scheduler->delay(10);
+            
+            // see if ICM20948 is sleeping
+            if (!dev_icm->read_registers(REG_ICM_PWR_MGMT_1, &rval, 1)) {
+                goto fail;
+            }
+            if ((rval & 0x40) == 0) {
+                break;
+            }
+        } while (retries--);
+       
+        if (rval & 0x40) {
+            // it didn't come out of sleep
             goto fail;
         }
-        if (rval & 0x40) {
-            // bring out of sleep mode, use internal oscillator
-            dev_icm->write_register(REG_ICM_PWR_MGMT_1, 0x00);
-            hal.scheduler->delay(10);
+
+        // initially force i2c bypass off
+        dev_icm->write_register(REG_ICM_INT_PIN_CFG, 0x00);
+        hal.scheduler->delay(1);
+
+        // now check if a AK09916 shows up on the bus. If it does then
+        // we have both a real AK09916 and a ICM20948 with an embedded
+        // AK09916. In that case we will fail the driver load and use
+        // the main AK09916 driver
+        uint16_t whoami;
+        if (dev->read_registers(REG_COMPANY_ID, (uint8_t *)&whoami, 2)) {
+            // a device is replying on the AK09916 I2C address, don't
+            // load the ICM20948
+            hal.console->printf("ICM20948: AK09916 bus conflict\n");
+            goto fail;
         }
-        // enable i2c bypass
+
+        // now force bypass on
         dev_icm->write_register(REG_ICM_INT_PIN_CFG, 0x02);
+        hal.scheduler->delay(1);
     }
 
     uint16_t whoami;