BBBCSIO

The SerialPortFS Class

Provides the Serial Port functionality for a BeagleBone Black. This is the SYSFS version

Be aware that you need to ensure the Serial port is configured in the Device Tree before this code will work. For more information on this see the Beaglebone Black and Device Tree Overlays Technical Note.

VERY IMPORTANT NOTE: The pins (including the serial port pins) on the Beaglebone Black are 3.3Volt. You CANNOT connect them up to a 5V serial device without level shifting the voltage or you will burn out the BBB. You DEFINITELY CANNOT connect them to the +/- 18V of a true RS232 serial port (on the back of a PC) because your BBB will instantly die.

Source Code

The source code for this class is available online for download and also in browseable form.

Example Code

Example code which demonstrates the use of this class can be found on the Serial Port Example page.

Syntax

public class SerialPortFS : PortFS

Provides the Serial Port functionality for a BeagleBone Black. (SYSFS version)

Public Constructors

public SerialPortFS(SerialPortEnum serialPortIn, SerialPortOpenModeEnum openMode) : base(GpioEnum.GPIO_NONE)

Constructor.

Parameters: serialPortIn - The serial port to use.; openMode - the read mode (BLOCK or NONBLOCK) in which we open the serial port.
The blocking mode refers to to the way the serial port code deals with a request to read more data than is present in the input queue. If the port is in OPEN_BLOCK mode and more data is requested than is present then the call will wait until the required amount of data arrives. In OPEN_NONBLOCK mode the port will just return what it has.

Public Methods

public void Break()

Removes all data from the Rx and Tx queues. The equivalent of the termios.c tcflush call

public override void ClosePort()

Closes the port.

public void DumpTermiosStruct(TermiosStruct xfer)

Dumps out the Termios structure to the console. For diagnostic purposes only.

public void Dispose()

Implements IDisposable. Should be called after the class is closed to release resources.

public void Flush()

Removes all data from the Rx and Tx queues. The equivalent of the termios.c tcflush call

public TermiosStruct GetTermiosState()

Gets the Termios structure. The equivalent of the termios.c tcgetattr call

public override PortDirectionEnum PortDirection()

Gets the PortDirection

Returns: A PortDirectionEnum value. This value is always PortDirectionEnum.PORTDIR_OUTPUT.

public int ReadByteArray(byte[] rxByteBuf, int numBytes)

Reads a buffer in from an Serial Device. We choose to structure this so that the caller passes in the byte array. This allows it to be re-used. If we just create and return one here then C# will have to deal with a lot of garbage collection (potentially) on very busy calls which would slow things down.

Parameters: rxByteBuf, The buffer in which we store the bytes read.; numBytes, The max number of bytes to read.

Returns: The number of bytes read.

public string ReadString(int maxBytes)

Reads a Serial Device and returns the contents as a string. This is not especially efficient in terms of memory use as both the return string and an intermediate byte[] array need to be created and subsequently garbage collected.

Parameters: numBytes, The max number of bytes to read.

Returns: a string with the contents of the serial port receive buffer up to the specified maxBytes. If nothing is ready to be read on the serial port an empty string will be returned.

public void SetTermiosState(ref TermiosStruct xfer)

Sets the Termios structure. The equivalent of the termios.c tcsetattr call.

Parameters: xfer, The termios structure to set.

public void Write(byte[] txByteBuf, int numBytes)

Writes a byte array out to an Serial Device.

Parameters: txByteBuf, The byte array buffer with bytes to write.; numBytes, The number of bytes to send

public void Write(string outStr)

Writes a string out to an Serial Device as a series of ASCII bytes.

Parameters: outStr, The string to write.

Public Properties

public SerialPortBaudRateEnum BaudRate { get; set; }

Gets/Sets the baud rate

value: A SerialPortBaudRateEnum value.

public SerialPortBitLengthEnum BitLength { get; set; }

Gets/Sets the bit length of the bytes transmitted via the BBB Serial port

value: A SerialPortBitLengthEnum value.

public int BytesInRxBuffer { get; }

Gets the number of pending (unread) bytes in the read buffer of the UART.

value: The number of pending (unread) bytes.

public SerialPortParityEnum Parity { get; set; }

Gets/Sets the parity bits of the bytes transmitted via the BBB Serial port

value: A SerialPortParityEnum value.

public SerialPortEnum SerialPort { get; }

Gets the Serial Port. There is no Set accessor this is set in the constructor.

value: A SerialPortEnum value.

public SerialPortStopBitsEnum StopBits { get; set; }

Gets/Sets the stop bit setting of the bytes transmitted via the BBB Serial port

value: A SerialPortStopBitsEnum value.