graham999au:
...
Plan B:Bypass Arduino. Run everything at Linux side.
AR9331 (Yun) one UART
AR9341 One low-speed UART (115 Kbps), one highspeed UART (3 Mbps)
AR9344 One low-speed UART (115 Kbps), one highspeed UART (3 Mbps)
QCA9558 One low-speed UART (115 Kbps), one highspeed UART (3 Mbps)
MT7628 two UART
MT7688 three UART