昨天非常晚的时候才最终发现事实上Unkown USB Device并非错误，仅仅是个警告而已，所以我们不关心就能够。让Makefile继续往下走就能够。于是我尝试mbs，s110。cload和firmware的下载。运行例如以下命令：

make flash
make flash_s110
make flash_mbs
make flash_cload

详细运行步骤例如以下：

bitcraze@bitcraze-vm:~/projects/crazyflie2-nrf-firmware$ make flash_mbs
openocd -d2 -f interface/stlink-v2.cfg -f target/nrf51_stlink.tcl -c init -c targets -c "reset halt"                  -c "flash write_image erase bootloaders/nrf_mbs_v1.0.hex" -c "verify_image bootloaders/nrf_mbs_v1.0.hex" -c "reset halt"                -c "mww 0x4001e504 0x01" -c "mww 0x10001014 0x3F000"                -c "reset run" -c shutdown
Open On-Chip Debugger 0.8.0 (2014-05-10-23:21)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.sourceforge.net/doc/doxygen/bugs.html
debug_level: 2
Info : This adapter doesn't support configurable speed
Info : STLINK v2 JTAG v16 API v2 SWIM v0 VID 0x0483 PID 0x3748
Info : using stlink api v2
Info : Target voltage: 2.556986
Info : nrf51.cpu: hardware has 4 breakpoints, 2 watchpoints
    TargetName         Type       Endian TapName            State       
--  ------------------ ---------- ------ ------------------ ------------
 0* nrf51.cpu          hla_target little nrf51.cpu          halted
target state: halted
target halted due to debug-request, current mode: Thread 
xPSR: 0xc1000000 pc: 0x000006d0 msp: 0x000007c0
auto erase enabled
Warn : Unknown device (HWID 0x00000058)
^CMakefile:122: recipe for target 'flash_mbs' failed
make: *** [flash_mbs] Interrupt

bitcraze@bitcraze-vm:~/projects/crazyflie2-nrf-firmware$ make flash_mbs
openocd -d2 -f interface/stlink-v2.cfg -f target/nrf51_stlink.tcl -c init -c targets -c "reset halt"                  -c "flash write_image erase bootloaders/nrf_mbs_v1.0.hex" -c "verify_image bootloaders/nrf_mbs_v1.0.hex" -c "reset halt"                -c "mww 0x4001e504 0x01" -c "mww 0x10001014 0x3F000"                -c "reset run" -c shutdown
Open On-Chip Debugger 0.8.0 (2014-05-10-23:21)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.sourceforge.net/doc/doxygen/bugs.html
debug_level: 2
Info : This adapter doesn't support configurable speed
Info : STLINK v2 JTAG v16 API v2 SWIM v0 VID 0x0483 PID 0x3748
Info : using stlink api v2
Info : Target voltage: 2.556986
Info : nrf51.cpu: hardware has 4 breakpoints, 2 watchpoints
    TargetName         Type       Endian TapName            State       
--  ------------------ ---------- ------ ------------------ ------------
 0* nrf51.cpu          hla_target little nrf51.cpu          halted
target state: halted
target halted due to debug-request, current mode: Thread 
xPSR: 0xc1000000 pc: 0x000006d0 msp: 0x000007c0
auto erase enabled
Warn : Unknown device (HWID 0x00000058)
wrote 3072 bytes from file bootloaders/nrf_mbs_v1.0.hex in 19.481831s (0.154 KiB/s)
target state: halted
target halted due to breakpoint, current mode: Thread 
xPSR: 0x61000000 pc: 0x2000002e msp: 0x000007c0
verified 2112 bytes in 0.288700s (7.144 KiB/s)
target state: halted
target halted due to debug-request, current mode: Thread 
xPSR: 0xc1000000 pc: 0x000006d0 msp: 0x000007c0
shutdown command invoked
bitcraze@bitcraze-vm:~/projects/crazyflie2-nrf-firmware$ make flash_cload
openocd -d2 -f interface/stlink-v2.cfg -f target/nrf51_stlink.tcl -c init -c targets -c "reset halt"                  -c "flash write_image erase bootloaders/cload_nrf_v1.0.hex" -c "verify_image bootloaders/cload_nrf_v1.0.hex" -c "reset halt"                -c "mww 0x4001e504 0x01" -c "mww 0x10001014 0x3F000"                -c "mww 0x4001e504 0x01" -c "mww 0x10001080 0x3A000" -c "reset run" -c shutdown
Open On-Chip Debugger 0.8.0 (2014-05-10-23:21)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.sourceforge.net/doc/doxygen/bugs.html
debug_level: 2
Info : This adapter doesn't support configurable speed
Info : STLINK v2 JTAG v16 API v2 SWIM v0 VID 0x0483 PID 0x3748
Info : using stlink api v2
Info : Target voltage: 2.556986
Info : nrf51.cpu: hardware has 4 breakpoints, 2 watchpoints
    TargetName         Type       Endian TapName            State       
--  ------------------ ---------- ------ ------------------ ------------
 0* nrf51.cpu          hla_target little nrf51.cpu          running
target state: halted
target halted due to debug-request, current mode: Thread 
xPSR: 0xc1000000 pc: 0x000006d0 msp: 0x000007c0
auto erase enabled
Warn : Unknown device (HWID 0x00000058)
wrote 13312 bytes from file bootloaders/cload_nrf_v1.0.hex in 82.957291s (0.157 KiB/s)
target state: halted
target halted due to breakpoint, current mode: Thread 
xPSR: 0x61000000 pc: 0x2000002e msp: 0x000007c0
verified 12368 bytes in 0.351360s (34.375 KiB/s)
target state: halted
target halted due to debug-request, current mode: Thread 
xPSR: 0xc1000000 pc: 0x000006d0 msp: 0x000007c0
shutdown command invoked
bitcraze@bitcraze-vm:~/projects/crazyflie2-nrf-firmware$ 
bitcraze@bitcraze-vm:~/projects/crazyflie2-nrf-firmware$ make flash_s110
openocd -d2 -f interface/stlink-v2.cfg -f target/nrf51_stlink.tcl -c init -c targets -c "reset halt"                  -c "nrf51 mass_erase"                  -c "flash write_image erase s110/s110_nrf51822_7.0.0_softdevice.hex"                  -c "reset run" -c shutdown
Open On-Chip Debugger 0.8.0 (2014-05-10-23:21)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.sourceforge.net/doc/doxygen/bugs.html
debug_level: 2
Info : This adapter doesn't support configurable speed
Info : STLINK v2 JTAG v16 API v2 SWIM v0 VID 0x0483 PID 0x3748
Info : using stlink api v2
Info : Target voltage: 2.558242
Info : nrf51.cpu: hardware has 4 breakpoints, 2 watchpoints
    TargetName         Type       Endian TapName            State       
--  ------------------ ---------- ------ ------------------ ------------
 0* nrf51.cpu          hla_target little nrf51.cpu          running
target state: halted
target halted due to debug-request, current mode: Thread 
xPSR: 0xc1000000 pc: 0x000006d0 msp: 0x000007c0
Warn : Unknown device (HWID 0x00000058)
auto erase enabled
Info : Padding image section 0 with 2112 bytes
wrote 87040 bytes from file s110/s110_nrf51822_7.0.0_softdevice.hex in 543.104126s (0.157 KiB/s)
shutdown command invoked
bitcraze@bitcraze-vm:~/projects/crazyflie2-nrf-firmware$ make flash
openocd -d2 -f interface/stlink-v2.cfg -f target/nrf51_stlink.tcl -c init -c targets -c "reset halt"                  -c "flash write_image erase cf2_nrf.hex" -c "verify_image cf2_nrf.hex"                  -c "reset run" -c shutdown
Open On-Chip Debugger 0.8.0 (2014-05-10-23:21)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.sourceforge.net/doc/doxygen/bugs.html
debug_level: 2
Info : This adapter doesn't support configurable speed
Info : STLINK v2 JTAG v16 API v2 SWIM v0 VID 0x0483 PID 0x3748
Info : using stlink api v2
Info : Target voltage: 2.558242
Info : nrf51.cpu: hardware has 4 breakpoints, 2 watchpoints
    TargetName         Type       Endian TapName            State       
--  ------------------ ---------- ------ ------------------ ------------
 0* nrf51.cpu          hla_target little nrf51.cpu          running
target state: halted
target halted due to debug-request, current mode: Thread 
xPSR: 0xc1000000 pc: 0x000006d0 msp: 0x000007c0
auto erase enabled
Warn : Unknown device (HWID 0x00000058)
wrote 45056 bytes from file cf2_nrf.hex in 282.951080s (0.156 KiB/s)
target state: halted
target halted due to breakpoint, current mode: Thread 
xPSR: 0x61000000 pc: 0x2000002e msp: 0x000007c0
verified 44944 bytes in 0.579762s (75.705 KiB/s)
shutdown command invoked

那事实上，在Makefile的最后，我们能够看到：

factory_reset:
	make mass_erase
ifeq ($(strip $(S110)),1)
	make flash_s110
	make flash_mbs
	make flash_cload
endif
	make flash

所以看上去假设S110=1，那么仅仅要运行make factory_reset就能够将s110，mbs。cload和firmware所有下载进去。不用分步进行，一键搞定，真爽！

昨天的研究也没白费。最终搞懂了。