Make sure OS handles are set correctly for unopened / closed ports.

[libserialport.git] / README

-------------------------------------------------------------------------------
libserialport: cross-platform library for accessing serial ports
-------------------------------------------------------------------------------

libserialport is a minimal library written in C that is intended to take care
of the OS-specific details when writing software that uses serial ports.

By writing your serial code to use libserialport, you enable it to work
transparently on any platform supported by the library.

The operations that are supported are:

- Port enumeration (obtaining a list of serial ports on the system).
- Opening and closing ports.
- Setting port parameters (baud rate, parity, etc).
- Reading, writing and flushing data.
- Obtaining error information.

libserialport is an open source project released under the LGPL3+ license.

Status
======

The library should build and work on any Windows or Unix-based system. If it
does not, please submit a bug.

Enumeration is currently only implemented on Windows, Mac OS X and Linux. On
other systems enumeration will return no results, but ports can still be opened
by name and then used.

If you know how to enumerate available ports on another OS, please submit a bug
with this information, or better still a patch implementing it.

Future
======

Future versions will add additional API calls for obtaining metadata about a
port, e.g. for USB devices the USB VID and PID of the underlying device.

Dependencies
============

On Linux, libudev is required. On other systems no other libraries are required.

The libudev dependency could be eliminated in favour of direct sysfs queries at
the cost of some brevity. This is not currently a priority but if you feel like
doing this feel free to submit a patch.

Building
========

The package uses a GNU style build system and requires a Unix style shell.
On Windows it can be built with the MinGW toolchain and MSYS environment.

Run "./autogen.sh" to generate the build system, "./configure" to setup, then
"make" to build the library and "make install" to install it.

API
===

The API is simple, and designed to be a minimal wrapper around the serial port
support in each OS.

Most functions take a pointer to a struct sp_port, which represents a serial
port. These structures are always allocated and freed by the library, using the
functions in the 'Enumeration' section below.

All functions can return only three possible error values. SP_ERR_ARG indicates
the function was called with invalid arguments. SP_ERR_FAIL indicates that the
OS reported a failure. SP_ERR_MEM indicates that a memory allocation failed.
All of these error values are negative.

When SP_ERR_FAIL is returned, an error code or string description of the error
can be obtained by calling sp_last_error_code() or sp_last_error_message(). The
error code or message is that provided by the OS; libserialport does not define
any error codes or messages of its own.

Function calls that succeed return SP_OK, which is equal to zero, or where
otherwise documented a positive value.

The available functions are as follows:

Enumeration
-----------

int sp_get_port_by_name(const char *portname, struct sp_port **port_ptr);

 Obtains a pointer to a new sp_port structure representing the named port. The
 user should allocate a variable of type "struct sp_port *" and pass a pointer
 to this to receive the result.

 The result should be freed after use by calling sp_free_port().
 
 Returns: SP_OK on success, SP_ERR_FAIL on failure, SP_ERR_MEM on allocation
          failure, or SP_ERR_ARG if an invalid pointer is passed. If any error
          is returned, the variable pointed to by port_ptr will be set to NULL.
          Otherwise, it will be set to point to the newly allocated port.

void sp_free_port(struct sp_port *port);

 Frees a port structure obtained from sp_get_port_by_name().

int sp_list_ports(struct sp_port ***list_ptr);

 Lists the serial ports available on the system. The result obtained is an
 array of pointers to sp_port structures, terminated by a NULL. The user should
 allocate a variable of type "struct sp_port **" and pass a pointer to this to
 receive the result.

 The result should be freed after use by calling sp_free_port_list(). If a port
 from the list is to be used after freeing the list, it must be copied first
 using sp_copy_port().

 Returns: SP_OK on success, SP_ERR_FAIL on failure, SP_ERR_MEM on allocation
          failure, or SP_ERR_ARG if an invalid pointer is passed. If any error
          is returned, the variable pointed to by list_ptr will be set to NULL.
          Otherwise, it will be set to point to the newly allocated array.

int sp_copy_port(const struct sp_port *port, struct sp_port **copy_ptr);

 Makes a new copy of a sp_port structure. The user should allocate a variable
 of type "struct sp_port *" and pass a pointer to this to receive the result.

 The copy should be freed after use by calling sp_free_port().

 Returns: SP_OK on success, SP_ERR_MEM on allocation failure, or SP_ERR_ARG
          if an invalid port or pointer is passed. If any error is returned,
          the variable pointed to by copy_ptr will be set to NULL. Otherwise,
          it will be set to point to the newly allocated copy.

void sp_free_port_list(struct sp_port **list);

 Frees a port list obtained from sp_list_ports(). This will also free all
 the sp_port structures referred to from the list; any that are to be retained
 must be copied first using sp_copy_port().

Opening and closing ports
-------------------------

int sp_open(struct sp_port *port, int flags);

 Opens the specified serial port.

 Parameters:

  port:      Pointer to port structure.
  flags:     Flags to use when opening the serial port. Possible
             flags are: SP_MODE_RDWR, SP_MODE_RDONLY, and SP_MODE_NONBLOCK.

 Returns: SP_OK on success, SP_ERR_FAIL on failure, SP_ERR_MEM on allocation
          failure, or SP_ERR_ARG if an invalid port is passed.

int sp_close(struct sp_port *port);

 Closes the specified serial port.

 Returns: SP_OK on success, SP_ERR_FAIL on failure, or SP_ERR_ARG
          if an invalid port is passed.

Setting port parameters
-----------------------

int sp_set_baudrate(struct sp_port *port, int baudrate)

 Sets the baud rate for the specified serial port.

 Parameters:

  port: Pointer to port structure.
  baud: Baud rate in bits per second.

 Returns: SP_OK on success, SP_ERR_FAIL on failure, or SP_ERR_ARG
          for invalid arguments.

int sp_set_bits(struct sp_port *port, int bits)

 Sets the number of data bits for the specified serial port.

 Parameters:

  port: Pointer to port structure.
  bits: Number of data bits to use. Valid values are 5 to 8.

 Returns: SP_OK on success, SP_ERR_FAIL on failure, or SP_ERR_ARG
          for invalid arguments.

int sp_set_parity(struct sp_port *port, int parity)

 Sets the parity for the specified serial port.

 Parameters:

  port:   Pointer to port structure.
  parity: Parity setting to use.
          (SP_PARITY_NONE, SP_PARITY_EVEN or SP_PARITY_ODD)

 Returns: SP_OK on success, SP_ERR_FAIL on failure, or SP_ERR_ARG
          for invalid arguments.

int sp_set_stopbits(struct sp_port *port, int stopbits)

 Sets the number of stop bits for the specified port.

 Parameters:

  port:     Pointer to port structure.
  stopbits: Number of stop bits to use (1 or 2).

 Returns: SP_OK on success, SP_ERR_FAIL on failure, or SP_ERR_ARG
          for invalid arguments.

int sp_set_flowcontrol(struct sp_port *port, int flowcontrol)

 Sets the flow control type for the specified serial port.

 This function is a wrapper that sets the RTS, CTS, DTR, DSR and
 XON/XOFF settings as necessary for the specified flow control
 type. For more fine-grained control of these settings, use their
 individual configuration functions or the sp_set_config() function.

 Parameters:

  port:        Pointer to port structure.
  flowcontrol: Flow control setting to use. Valid settings are:

   SP_FLOWCONTROL_NONE: No flow control.
   SP_FLOWCONTROL_XONXOFF: Software flow control using XON/XOFF characters.
   SP_FLOWCONTROL_RTSCTS: Hardware flow control using RTS/CTS signals.
   SP_FLOWCONTROL_DTRDSR: Hardware flow control using DTR/DSR signals.

 Returns: SP_OK on success, SP_ERR_FAIL on failure, or SP_ERR_ARG
          for invalid arguments.

int sp_set_config(struct sp_port *port, struct sp_port_config *config)

 Sets all parameters for the specified serial port.

 The user should populate a struct sp_port_config, then pass a pointer to it
 as the config parameter.

 The fields of sp_port_config are:

  int baudrate: Baud rate in bits per second.
  int bits:     Number of data bits to use. Valid values are 5 to 8.
  int parity:   Parity setting to use.
                 (SP_PARITY_NONE, SP_PARITY_EVEN or SP_PARITY_ODD)
  int stopbits: Number of stop bits to use (1 or 2).
  int rts:      RTS pin mode.
                 (SP_RTS_ON, SP_RTS_OFF or SP_RTS_FLOW_CONTROL)
  int cts:      CTS pin mode.
                 (SP_CTS_IGNORE or SP_CTS_FLOW_CONTROL)
  int dtr:      DTR pin mode.
                 (SP_DTR_ON, SP_DTR_OFF or SP_DTR_FLOW_CONTROL)
  int dsr:      DSR pin mode.
                 (SP_DSR_IGNORE or SP_DSR_FLOW_CONTROL)
  int xon_xoff: XON/XOFF flow control mode.
                 (SP_XONXOFF_DISABLED, SP_XONXOFF_IN,
                  SP_XONXOFF_OUT or SP_XONXOFF_INOUT)

 To retain the current value of any setting, set the field to to a
 negative value.

 Returns: SP_OK on success, SP_ERR_FAIL on failure, or SP_ERR_ARG
          for invalid arguments.

Reading, writing and flushing data
----------------------------------

int sp_read(struct sp_port *port, const void *buf, size_t count)

 Reads bytes from the specified serial port. Note that this function may
 return after reading less than the specified number of bytes; it is the
 user's responsibility to iterate as necessary in this case.

 Parameters:

  port:  Pointer to port structure.
  buf:   Buffer in which to store the bytes read.
  count: Maximum number of bytes to read.

 Returns: The number of bytes read, SP_ERR_FAIL on failure,
          or SP_ERR_ARG for invalid arguments.

int sp_write(struct sp_port *port, const void *buf, size_t count)

 Write bytes to the specified serial port. Note that this function may
 return after writing less than the specified number of bytes; it is the
 user's responsibility to iterate as necessary in this case.

 Parameters:

  port:  Pointer to port structure.
  buf:   Buffer containing the bytes to write.
  count: Maximum number of bytes to write.

 Returns: The number of bytes written, SP_ERR_FAIL on failure,
          or SP_ERR_ARG for invalid arguments.

int sp_flush(struct sp_port *port);

 Flushes serial port buffers.

 Returns: SP_OK on success, SP_ERR_FAIL on failure, or SP_ERR_ARG
          if an invalid port is passed.

Error handling
--------------

int sp_last_error_code();

 Gets the error code for a failed operation.

 In order to obtain the correct result, this function should be called
 straight after the failure, before executing any other system operations.

 Returns: The system's numeric code for the error that caused the last
          operation to fail.

char *sp_last_error_message();

 Gets the error message for failed operation.

 In order to obtain the correct result, this function should be called
 straight after the failure, before executing other system operations.

 Returns: The system's message for the error that caused the last
          operation to fail. This string may be allocated by the function,
          and should be freed after use by calling sp_free_error_message.

void sp_free_error_message(char *message);

 Frees the error message returned by sp_last_error_message().