You can optionally receive the output data over a serial connection in addition to USB. The data format is the same as USB - a stream of newline separated JSON objects.
In the same way that you can send OpenXC writes over USB using the OUT direction of the USB endpoint, you can send identically formatted messages in the opposite direction on the serial device - from the host to the CAN translator. They’ll be processed in exactly the same way. These write messages are accepted via serial even if USB is connected.
On the chipKIT, UART1A is used for OpenXC output at the 460800 baud rate. Hardware flow control (RTS/CTS) is enabled, so CTS must be pulled low by the receiving device before data will be sent.
UART1A is also used by the USB-Serial connection, so in order to flash the PIC32, the Tx/Rx lines must be disconnected. Ideally we could leave that UART interface for debugging, but there are conflicts with all other exposed UART interfaces when using flow control.
On the NGX Blueboard LPC1768-H, UART1 is used for OpenXC output at the 921600 baud rate. Like on the chipKIT, hardware flow control (RTS/CTS) is enabled, so CTS must be pulled low by the receiving device before data will be sent.