update instructions for BNO055 firmware update

doc/BNO055_Firmware_Update.md

@@ -1,11 +1,17 @@
 ## update procedure
 
+Before updating BNO055 firmware via the `9DOF Debug` debugging interface, the Ambiq chip should be flashed with a firmware (such as `test_buzzer.c`) that does not activate BNO055, otherwise the JLink connection would not be established.
+
 ```bash
 #start JLink 
 JLinkExe -Device ATSAMD20J18A -if SWD -speed 4000 -AutoConnect 1
 
 #inside JLink program
+#option 1: this load the firmware, not including the bootloader
 loadbin mybno.bin 0x4000
+
+#option 2: this load the full firmware, including the bootloader
+loadbin full.bin 0x0000
 ```
 
 ## save older firmware
@@ -14,7 +20,8 @@ you can save the original bootloader or the firmware, just incase something goes
 
 ```
 savebin bl.bin 0x0000 0x4000 //save the bootloader, from start up to address 0x4000
-savebin saved.bin 0x4000 0x3C000 //save the firmware
+savebin saved.bin 0x4000 0x3C000 //save the firmware, not including the bootloader
+savebin full.bin 0x0000 0x3c00 //save the full firmware, including the bootloader
 ```
 
 on a trial device, load the saved firmware