add realtime kws example for stm32f4xx

[xiongyihui]

realtime KWS using audio from STM32F4xx‘s 12 bit ADC & a microphone.

Tested with Seeed Arch Max (STM32F407)

[zixiao1511034]

Hi Yihui，

Your code is exactly what I'm looking for!
But I have trouble with the scratch_buffer. I cannot pass it to KWS_DS_CNN kws.
Can you explain KWS kws(audio_buffer,scratch_buffer) to me? Did you make any modification to it to receive the scratch_buffer[16000]?

Thanks,
Shawn

[xiongyihui]

I haven't tried the DS_CNN network. At that time, just DNN was available.
You need make some changes to make it work with DS_CNN.