USB_COMM Using OSX Terminal and Serial2 Example


I have compiled the serial2 example provided in the libpololu-avr package on my SVP-1284P but I cannot get it to transmit bytes as the program descriptions mention.

I am using the OSX10.8 Terminal and tried echo G>/dev/tty.usbmodem00026041, I know something is working because the green LED next to the USB port on the SVP flashes when I make the call but Terminal doesn’t seem to execute the command and I must exit the call manually.

What are the correct commands for communicating via the USB_COMM port using Terminal? Are there more examples for using the serial interface? Ultimately, I hope to communicate with a UART Bluetooth module which will transmit data gathered by the SVP to a Java program running on my laptop.

Thank you in advance for your help!

For reference, here is Serial2

[code]#include <pololu/orangutan.h>


  • serial2: for the Orangutan SVP and Orangutan X2 controllers.
  • This example listens for serial bytes transmitted via USB to the controller’s
  • virtual COM port (USB_COMM). Whenever it receives a byte, it performs a
  • custom action. Whenever the user presses the middle button, it transmits a
  • greeting to the virtual COM port.
  • This example will not work on the Orangutan LV, SV, Baby Orangutan, or 3pi robot.

// receive_buffer: A ring buffer that we will use to receive bytes on USB_COMM.
// The OrangutanSerial library will put received bytes in to
// the buffer starting at the beginning (receiveBuffer[0]).
// After the buffer has been filled, the library will automatically
// start over at the beginning.
char receive_buffer[32];

// receive_buffer_position: This variable will keep track of which bytes in the receive buffer
// we have already processed. It is the offset (0-31) of the next byte
// in the buffer to process.
unsigned char receive_buffer_position = 0;

// send_buffer: A buffer for sending bytes on USB_COMM.
char send_buffer[32];

// wait_for_sending_to_finish: Waits for the bytes in the send buffer to
// finish transmitting on USB_COMM. We must call this before modifying
// send_buffer or trying to send more bytes, because otherwise we could
// corrupt an existing transmission.
void wait_for_sending_to_finish()
serial_check(); // USB_COMM port is always in SERIAL_CHECK mode

// process_received_byte: Responds to a byte that has been received on
// USB_COMM. If you are writing your own serial program, you can
// replace all the code in this function with your own custom behaviors.
void process_received_byte(char byte)
clear(); // clear LCD
print("RX: ");
lcd_goto_xy(0, 1); // go to start of second LCD row

	// If the character 'G' or 'g' is received, toggle the green LED.
	case 'G':
	case 'g':
		print("green LED");

	// If the character 'R' or 'r' is received, toggle the red LED.
	case 'R':
	case 'r':
		print("red LED");

	// If the character 'C' or 'c' is received, play the note C.
	case 'C':
	case 'c':
		print("play note C");

	// If the character 'D' or 'd' is received, play the note D.
	case 'D':
	case 'd':
		print("play note D");

	// If any other character is received, change its capitalization and
	// send it back.
		send_buffer[0] = byte ^ 0x20;
		serial_send(USB_COMM, send_buffer, 1);
		print("TX: ");


void check_for_new_bytes_received()
while(serial_get_received_bytes(USB_COMM) != receive_buffer_position)
// Process the new byte that has just been received.

	// Increment receive_buffer_position, but wrap around when it gets to
	// the end of the buffer. 
	if (receive_buffer_position == sizeof(receive_buffer)-1)
		receive_buffer_position = 0;


int main()
clear(); // clear the LCD
print(“Send serial”);
lcd_goto_xy(0, 1); // go to start of second LCD row
print(“or press B”);

// Set the baud rate to 9600 bits per second.  Each byte takes ten bit
// times, so you can get at most 960 bytes per second at this speed.
serial_set_baud_rate(USB_COMM, 9600);

// Start receiving bytes in the ring buffer.
serial_receive_ring(USB_COMM, receive_buffer, sizeof(receive_buffer));

	// USB_COMM is always in SERIAL_CHECK mode, so we need to call this
	// function often to make sure serial receptions and transmissions
	// occur.

	// Deal with any new bytes received.

	// If the user presses the middle button, send "Hi there!"
	// and wait until the user releases the button.
	if (button_is_pressed(MIDDLE_BUTTON))
		memcpy_P(send_buffer, PSTR("Hi there!\r\n"), 11);
		serial_send(USB_COMM, send_buffer, 11);
		send_buffer[11] = 0;	// terminate the string
		clear();				// clear the LCD
		lcd_goto_xy(0, 1);		// go to start of second LCD row
		print("TX: ");

		// Wait for the user to release the button.  While the processor is
		// waiting, the OrangutanSerial library will not be able to receive
		// bytes from the USB_COMM port since this requires calls to the
		// serial_check() function, which could cause serial bytes to be
		// lost.  It will also not be able to send any bytes, so the bytes
		// bytes we just queued for transmission will not be sent until
		// after the following blocking function exits once the button is
		// released.  If any of this is a concern, you can replace the
		// following line with:
		// do
		// {
		//   while (button_is_pressed(MIDDLE_BUTTON))
		//     serial_check();	// receive and transmit as needed
		//   delay_ms(10);		// debounce the button press/release
		// }
		// while (button_is_pressed(MIDDLE_BUTTON));


UPDATE: In case anyone else runs into this issue or cares about USB_COMM through the Terminal application.

Apparently the correct command to use for interfacing is:

screen /dev/tty.usbmodem###### 9600

The usbmodem number is not the lowest number when calling ls /dev/tty.usb*, I found this out the hard way. When looking through my System Report, I noticed the device showed up as Pololu Orangutan SVP and the correct serial (usbmodem) number is listed. I ran screen again and got the example to work! :mrgreen:

Does anyone have experience interfacing with a UART Bluetooth module and could recommend a specific module?