Serial channels can be arbitrary assigned to specific functionality. Please check next lines in the main.c in INS application example:
platformUnassignSerialChannels();
BOOL res;
res = platformAssignPortTypeToSerialChannel(USER_SERIAL_PORT, UART_CHANNEL_0);
while(!res){}; // check if valid
res = platformAssignPortTypeToSerialChannel(DEBUG_SERIAL_PORT, UART_CHANNEL_1);
while(!res){}; // check if valid
res = platformAssignPortTypeToSerialChannel(GPS_SERIAL_PORT, UART_CHANNEL_2);
while(!res){}; // check if valid
Andrey