==requirements==
Inside a train, we should have:

*exactly 2 driver intercom consoles
*multiple 1-key devices located at cabins
*multiple amplifiers mounted on the ceiling of cabins and several external amplifiers speakers

All connected within the LAN.

Plz implement following keys, LEDs and functions:

===keys===
# key1 for driver direct intercom.
# key2 for driver pickup any call.
# key3 for hung up all current calls OR reject an incoming call.. 
# key4 for internal board casting, press key3 to terminate.
# key5 for external board casting, press key3 to terminate.

===led===
# LED1 blinking unaccepted incoming intercom calls, on established intercom calls 
# LED2 blinking unaccepted incoming emergency calls, on established emergency calls 
# LED3 on internal broadcasting
# LED4 on external broadcasting


==pin脚定义==

==protocols==

===LED protocols===
*AM335x sends command to STM32 to drive LEDs
'''通讯协议说明：'''
*例如：0xa5 0x00 0xff 0x01 0x02 0x03 0x04 0x5a,其中0xa5为帧头，0x5a为帧尾，0x00表示第一个灯常灭，0xff表示第二个灯常亮，0x01表示1s闪烁一次，0x02表示1s闪烁2次，依次类推...