new audio engine backend for native CoreAudio audio I/O, and PortMIDI for MIDI.

Code builds, runs and functions. Full code review still pending, and some possibly changes to organization of code within the backend is possible

1 files changed, 654 insertions, 0 deletions

diff --git a/libs/backends/wavesaudio/portmidi/portmidi.h b/libs/backends/wavesaudio/portmidi/portmidi.h
new file mode 100644
index 0000000000..e07991e0d6
--- /dev/null
+++ b/libs/backends/wavesaudio/portmidi/portmidi.h
@@ -0,0 +1,654 @@
+#ifndef PORT_MIDI_H
+#define PORT_MIDI_H
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+/*
+ * PortMidi Portable Real-Time MIDI Library
+ * PortMidi API Header File
+ * Latest version available at: http://sourceforge.net/projects/portmedia
+ *
+ * Copyright (c) 1999-2000 Ross Bencina and Phil Burk
+ * Copyright (c) 2001-2006 Roger B. Dannenberg
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files
+ * (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge,
+ * publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR
+ * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
+ * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+/*
+ * The text above constitutes the entire PortMidi license; however, 
+ * the PortMusic community also makes the following non-binding requests:
+ *
+ * Any person wishing to distribute modifications to the Software is
+ * requested to send the modifications to the original developer so that
+ * they can be incorporated into the canonical version. It is also
+ * requested that these non-binding requests be included along with the 
+ * license above.
+ */
+
+/* CHANGELOG FOR PORTMIDI
+ *     (see ../CHANGELOG.txt)
+ *
+ * NOTES ON HOST ERROR REPORTING: 
+ *
+ *    PortMidi errors (of type PmError) are generic, system-independent errors.
+ *    When an error does not map to one of the more specific PmErrors, the
+ *    catch-all code pmHostError is returned. This means that PortMidi has
+ *    retained a more specific system-dependent error code. The caller can
+ *    get more information by calling Pm_HasHostError() to test if there is
+ *    a pending host error, and Pm_GetHostErrorText() to get a text string
+ *    describing the error. Host errors are reported on a per-device basis 
+ *    because only after you open a device does PortMidi have a place to 
+ *    record the host error code. I.e. only 
+ *    those routines that receive a (PortMidiStream *) argument check and 
+ *    report errors. One exception to this is that Pm_OpenInput() and 
+ *    Pm_OpenOutput() can report errors even though when an error occurs,
+ *    there is no PortMidiStream* to hold the error. Fortunately, both
+ *    of these functions return any error immediately, so we do not really
+ *    need per-device error memory. Instead, any host error code is stored
+ *    in a global, pmHostError is returned, and the user can call 
+ *    Pm_GetHostErrorText() to get the error message (and the invalid stream
+ *    parameter will be ignored.) The functions 
+ *    pm_init and pm_term do not fail or raise
+ *    errors. The job of pm_init is to locate all available devices so that
+ *    the caller can get information via PmDeviceInfo(). If an error occurs,
+ *    the device is simply not listed as available.
+ *
+ *    Host errors come in two flavors:
+ *      a) host error 
+ *      b) host error during callback
+ *    These can occur w/midi input or output devices. (b) can only happen 
+ *    asynchronously (during callback routines), whereas (a) only occurs while
+ *    synchronously running PortMidi and any resulting system dependent calls.
+ *    Both (a) and (b) are reported by the next read or write call. You can
+ *    also query for asynchronous errors (b) at any time by calling
+ *    Pm_HasHostError().
+ *
+ * NOTES ON COMPILE-TIME SWITCHES
+ *
+ *    DEBUG assumes stdio and a console. Use this if you want automatic, simple
+ *        error reporting, e.g. for prototyping. If you are using MFC or some 
+ *        other graphical interface with no console, DEBUG probably should be
+ *        undefined.
+ *    PM_CHECK_ERRORS more-or-less takes over error checking for return values,
+ *        stopping your program and printing error messages when an error
+ *        occurs. This also uses stdio for console text I/O.
+ */
+
+#ifndef WIN32
+// Linux and OS X have stdint.h
+#include <stdint.h>
+#else
+#ifndef INT32_DEFINED
+// rather than having users install a special .h file for windows, 
+// just put the required definitions inline here. porttime.h uses
+// these too, so the definitions are (unfortunately) duplicated there
+typedef int int32_t;
+typedef unsigned int uint32_t;
+#define INT32_DEFINED
+#endif
+#endif
+
+#ifdef _WINDLL
+#define PMEXPORT __declspec(dllexport)
+#else
+#define PMEXPORT 
+#endif
+
+#ifndef FALSE
+    #define FALSE 0
+#endif
+#ifndef TRUE
+    #define TRUE 1
+#endif
+
+/* default size of buffers for sysex transmission: */
+#define PM_DEFAULT_SYSEX_BUFFER_SIZE 1024
+
+/** List of portmidi errors.*/
+typedef enum {
+    pmNoError = 0,
+    pmNoData = 0, /**< A "no error" return that also indicates no data avail. */
+    pmGotData = 1, /**< A "no error" return that also indicates data available */
+    pmHostError = -10000,
+    pmInvalidDeviceId, /** out of range or 
+                        * output device when input is requested or 
+                        * input device when output is requested or
+                        * device is already opened 
+                        */
+    pmInsufficientMemory,
+    pmBufferTooSmall,
+    pmBufferOverflow,
+    pmBadPtr, /* PortMidiStream parameter is NULL or
+               * stream is not opened or
+               * stream is output when input is required or
+               * stream is input when output is required */
+    pmBadData, /** illegal midi data, e.g. missing EOX */
+    pmInternalError,
+    pmBufferMaxSize /** buffer is already as large as it can be */
+    /* NOTE: If you add a new error type, be sure to update Pm_GetErrorText() */
+} PmError;
+
+/**
+    Pm_Initialize() is the library initialisation function - call this before
+    using the library.
+*/
+PMEXPORT PmError Pm_Initialize( void );
+
+/**
+    Pm_Terminate() is the library termination function - call this after
+    using the library.
+*/
+PMEXPORT PmError Pm_Terminate( void );
+
+/**  A single PortMidiStream is a descriptor for an open MIDI device.
+*/
+typedef void PortMidiStream;
+#define PmStream PortMidiStream
+
+/**
+    Test whether stream has a pending host error. Normally, the client finds
+    out about errors through returned error codes, but some errors can occur
+    asynchronously where the client does not
+    explicitly call a function, and therefore cannot receive an error code.
+    The client can test for a pending error using Pm_HasHostError(). If true,
+    the error can be accessed and cleared by calling Pm_GetErrorText(). 
+    Errors are also cleared by calling other functions that can return
+    errors, e.g. Pm_OpenInput(), Pm_OpenOutput(), Pm_Read(), Pm_Write(). The
+    client does not need to call Pm_HasHostError(). Any pending error will be
+    reported the next time the client performs an explicit function call on 
+    the stream, e.g. an input or output operation. Until the error is cleared,
+    no new error codes will be obtained, even for a different stream.
+*/
+PMEXPORT int Pm_HasHostError( PortMidiStream * stream );
+
+
+/**  Translate portmidi error number into human readable message.
+    These strings are constants (set at compile time) so client has 
+    no need to allocate storage
+*/
+PMEXPORT const char *Pm_GetErrorText( PmError errnum );
+
+/**  Translate portmidi host error into human readable message.
+    These strings are computed at run time, so client has to allocate storage.
+    After this routine executes, the host error is cleared. 
+*/
+PMEXPORT void Pm_GetHostErrorText(char * msg, unsigned int len);
+
+#define HDRLENGTH 50
+#define PM_HOST_ERROR_MSG_LEN 256u /* any host error msg will occupy less 
+                                      than this number of characters */
+
+/**
+    Device enumeration mechanism.
+
+    Device ids range from 0 to Pm_CountDevices()-1.
+
+*/
+typedef int PmDeviceID;
+#define pmNoDevice -1
+typedef struct {
+    int structVersion; /**< this internal structure version */ 
+    const char *interf; /**< underlying MIDI API, e.g. MMSystem or DirectX */
+    const char *name;   /**< device name, e.g. USB MidiSport 1x1 */
+    int input; /**< true iff input is available */
+    int output; /**< true iff output is available */
+    int opened; /**< used by generic PortMidi code to do error checking on arguments */
+
+} PmDeviceInfo;
+
+/**  Get devices count, ids range from 0 to Pm_CountDevices()-1. */
+PMEXPORT int Pm_CountDevices( void );
+/**
+    Pm_GetDefaultInputDeviceID(), Pm_GetDefaultOutputDeviceID()
+
+    Return the default device ID or pmNoDevice if there are no devices.
+    The result (but not pmNoDevice) can be passed to Pm_OpenMidi().
+    
+    The default device can be specified using a small application
+    named pmdefaults that is part of the PortMidi distribution. This
+    program in turn uses the Java Preferences object created by
+    java.util.prefs.Preferences.userRoot().node("/PortMidi"); the
+    preference is set by calling 
+        prefs.put("PM_RECOMMENDED_OUTPUT_DEVICE", prefName);
+    or  prefs.put("PM_RECOMMENDED_INPUT_DEVICE", prefName);
+    
+    In the statements above, prefName is a string describing the
+    MIDI device in the form "interf, name" where interf identifies
+    the underlying software system or API used by PortMdi to access
+    devices and name is the name of the device. These correspond to 
+    the interf and name fields of a PmDeviceInfo. (Currently supported
+    interfaces are "MMSystem" for Win32, "ALSA" for Linux, and 
+    "CoreMIDI" for OS X, so in fact, there is no choice of interface.)
+    In "interf, name", the strings are actually substrings of 
+    the full interface and name strings. For example, the preference 
+    "Core, Sport" will match a device with interface "CoreMIDI"
+    and name "In USB MidiSport 1x1". It will also match "CoreMIDI"
+    and "In USB MidiSport 2x2". The devices are enumerated in device
+    ID order, so the lowest device ID that matches the pattern becomes
+    the default device. Finally, if the comma-space (", ") separator
+    between interface and name parts of the preference is not found,
+    the entire preference string is interpreted as a name, and the
+    interface part is the empty string, which matches anything.
+
+    On the MAC, preferences are stored in 
+      /Users/$NAME/Library/Preferences/com.apple.java.util.prefs.plist
+    which is a binary file. In addition to the pmdefaults program,
+    there are utilities that can read and edit this preference file.
+
+    On the PC, 
+
+    On Linux, 
+
+*/
+PMEXPORT PmDeviceID Pm_GetDefaultInputDeviceID( void );
+/** see PmDeviceID Pm_GetDefaultInputDeviceID() */
+PMEXPORT PmDeviceID Pm_GetDefaultOutputDeviceID( void );
+
+/**
+    PmTimestamp is used to represent a millisecond clock with arbitrary
+    start time. The type is used for all MIDI timestampes and clocks.
+*/
+typedef int32_t PmTimestamp;
+typedef PmTimestamp (*PmTimeProcPtr)(void *time_info);
+
+/** TRUE if t1 before t2 */
+#define PmBefore(t1,t2) ((t1-t2) < 0)
+/** 
+    \defgroup grp_device Input/Output Devices Handling
+    @{
+*/
+/**
+    Pm_GetDeviceInfo() returns a pointer to a PmDeviceInfo structure
+    referring to the device specified by id.
+    If id is out of range the function returns NULL.
+
+    The returned structure is owned by the PortMidi implementation and must
+    not be manipulated or freed. The pointer is guaranteed to be valid
+    between calls to Pm_Initialize() and Pm_Terminate().
+*/
+PMEXPORT const PmDeviceInfo* Pm_GetDeviceInfo( PmDeviceID id );
+
+/**
+    Pm_OpenInput() and Pm_OpenOutput() open devices.
+
+    stream is the address of a PortMidiStream pointer which will receive
+    a pointer to the newly opened stream.
+
+    inputDevice is the id of the device used for input (see PmDeviceID above).
+
+    inputDriverInfo is a pointer to an optional driver specific data structure
+    containing additional information for device setup or handle processing.
+    inputDriverInfo is never required for correct operation. If not used
+    inputDriverInfo should be NULL.
+
+    outputDevice is the id of the device used for output (see PmDeviceID above.)
+
+    outputDriverInfo is a pointer to an optional driver specific data structure
+    containing additional information for device setup or handle processing.
+    outputDriverInfo is never required for correct operation. If not used
+    outputDriverInfo should be NULL.
+
+    For input, the buffersize specifies the number of input events to be 
+    buffered waiting to be read using Pm_Read(). For output, buffersize 
+    specifies the number of output events to be buffered waiting for output. 
+    (In some cases -- see below -- PortMidi does not buffer output at all
+    and merely passes data to a lower-level API, in which case buffersize
+    is ignored.)
+    
+    latency is the delay in milliseconds applied to timestamps to determine 
+    when the output should actually occur. (If latency is < 0, 0 is assumed.) 
+    If latency is zero, timestamps are ignored and all output is delivered
+    immediately. If latency is greater than zero, output is delayed until the
+    message timestamp plus the latency. (NOTE: the time is measured relative 
+    to the time source indicated by time_proc. Timestamps are absolute,
+    not relative delays or offsets.) In some cases, PortMidi can obtain
+    better timing than your application by passing timestamps along to the
+    device driver or hardware. Latency may also help you to synchronize midi
+    data to audio data by matching midi latency to the audio buffer latency.
+
+    time_proc is a pointer to a procedure that returns time in milliseconds. It
+    may be NULL, in which case a default millisecond timebase (PortTime) is 
+    used. If the application wants to use PortTime, it should start the timer
+    (call Pt_Start) before calling Pm_OpenInput or Pm_OpenOutput. If the
+    application tries to start the timer *after* Pm_OpenInput or Pm_OpenOutput,
+    it may get a ptAlreadyStarted error from Pt_Start, and the application's
+    preferred time resolution and callback function will be ignored.
+    time_proc result values are appended to incoming MIDI data, and time_proc
+    times are used to schedule outgoing MIDI data (when latency is non-zero).
+
+    time_info is a pointer passed to time_proc.
+
+    Example: If I provide a timestamp of 5000, latency is 1, and time_proc
+    returns 4990, then the desired output time will be when time_proc returns
+    timestamp+latency = 5001. This will be 5001-4990 = 11ms from now.
+
+    return value:
+    Upon success Pm_Open() returns PmNoError and places a pointer to a
+    valid PortMidiStream in the stream argument.
+    If a call to Pm_Open() fails a nonzero error code is returned (see
+    PMError above) and the value of port is invalid.
+
+    Any stream that is successfully opened should eventually be closed
+    by calling Pm_Close().
+
+*/
+PMEXPORT PmError Pm_OpenInput( PortMidiStream** stream,
+                PmDeviceID inputDevice,
+                void *inputDriverInfo,
+                int32_t bufferSize,
+                PmTimeProcPtr time_proc,
+                void *time_info );
+
+PMEXPORT PmError Pm_OpenOutput( PortMidiStream** stream,
+                PmDeviceID outputDevice,
+                void *outputDriverInfo,
+                int32_t bufferSize,
+                PmTimeProcPtr time_proc,
+                void *time_info,
+                int32_t latency );
+  /** @} */
+
+/**
+   \defgroup grp_events_filters Events and Filters Handling
+   @{
+*/
+
+/*  \function PmError Pm_SetFilter( PortMidiStream* stream, int32_t filters )
+    Pm_SetFilter() sets filters on an open input stream to drop selected
+    input types. By default, only active sensing messages are filtered.
+    To prohibit, say, active sensing and sysex messages, call
+    Pm_SetFilter(stream, PM_FILT_ACTIVE | PM_FILT_SYSEX);
+
+    Filtering is useful when midi routing or midi thru functionality is being
+    provided by the user application.
+    For example, you may want to exclude timing messages (clock, MTC, start/stop/continue),
+    while allowing note-related messages to pass.
+    Or you may be using a sequencer or drum-machine for MIDI clock information but want to
+    exclude any notes it may play.
+ */
+    
+/* Filter bit-mask definitions */
+/** filter active sensing messages (0xFE): */
+#define PM_FILT_ACTIVE (1 << 0x0E)
+/** filter system exclusive messages (0xF0): */
+#define PM_FILT_SYSEX (1 << 0x00)
+/** filter MIDI clock message (0xF8) */
+#define PM_FILT_CLOCK (1 << 0x08)
+/** filter play messages (start 0xFA, stop 0xFC, continue 0xFB) */
+#define PM_FILT_PLAY ((1 << 0x0A) | (1 << 0x0C) | (1 << 0x0B))
+/** filter tick messages (0xF9) */
+#define PM_FILT_TICK (1 << 0x09)
+/** filter undefined FD messages */
+#define PM_FILT_FD (1 << 0x0D)
+/** filter undefined real-time messages */
+#define PM_FILT_UNDEFINED PM_FILT_FD
+/** filter reset messages (0xFF) */
+#define PM_FILT_RESET (1 << 0x0F)
+/** filter all real-time messages */
+#define PM_FILT_REALTIME (PM_FILT_ACTIVE | PM_FILT_SYSEX | PM_FILT_CLOCK | \
+    PM_FILT_PLAY | PM_FILT_UNDEFINED | PM_FILT_RESET | PM_FILT_TICK)
+/** filter note-on and note-off (0x90-0x9F and 0x80-0x8F */
+#define PM_FILT_NOTE ((1 << 0x19) | (1 << 0x18))
+/** filter channel aftertouch (most midi controllers use this) (0xD0-0xDF)*/
+#define PM_FILT_CHANNEL_AFTERTOUCH (1 << 0x1D)
+/** per-note aftertouch (0xA0-0xAF) */
+#define PM_FILT_POLY_AFTERTOUCH (1 << 0x1A)
+/** filter both channel and poly aftertouch */
+#define PM_FILT_AFTERTOUCH (PM_FILT_CHANNEL_AFTERTOUCH | PM_FILT_POLY_AFTERTOUCH)
+/** Program changes (0xC0-0xCF) */
+#define PM_FILT_PROGRAM (1 << 0x1C)
+/** Control Changes (CC's) (0xB0-0xBF)*/
+#define PM_FILT_CONTROL (1 << 0x1B)
+/** Pitch Bender (0xE0-0xEF*/
+#define PM_FILT_PITCHBEND (1 << 0x1E)
+/** MIDI Time Code (0xF1)*/
+#define PM_FILT_MTC (1 << 0x01)
+/** Song Position (0xF2) */
+#define PM_FILT_SONG_POSITION (1 << 0x02)
+/** Song Select (0xF3)*/
+#define PM_FILT_SONG_SELECT (1 << 0x03)
+/** Tuning request (0xF6)*/
+#define PM_FILT_TUNE (1 << 0x06)
+/** All System Common messages (mtc, song position, song select, tune request) */
+#define PM_FILT_SYSTEMCOMMON (PM_FILT_MTC | PM_FILT_SONG_POSITION | PM_FILT_SONG_SELECT | PM_FILT_TUNE)
+
+
+PMEXPORT PmError Pm_SetFilter( PortMidiStream* stream, int32_t filters );
+
+#define Pm_Channel(channel) (1<<(channel))
+/**
+    Pm_SetChannelMask() filters incoming messages based on channel.
+    The mask is a 16-bit bitfield corresponding to appropriate channels.
+    The Pm_Channel macro can assist in calling this function.
+    i.e. to set receive only input on channel 1, call with
+    Pm_SetChannelMask(Pm_Channel(1));
+    Multiple channels should be OR'd together, like
+    Pm_SetChannelMask(Pm_Channel(10) | Pm_Channel(11))
+
+    Note that channels are numbered 0 to 15 (not 1 to 16). Most 
+    synthesizer and interfaces number channels starting at 1, but
+    PortMidi numbers channels starting at 0.
+
+    All channels are allowed by default
+*/
+PMEXPORT PmError Pm_SetChannelMask(PortMidiStream *stream, int mask);
+
+/**
+    Pm_Abort() terminates outgoing messages immediately
+    The caller should immediately close the output port;
+    this call may result in transmission of a partial midi message.
+    There is no abort for Midi input because the user can simply
+    ignore messages in the buffer and close an input device at
+    any time.
+ */
+PMEXPORT PmError Pm_Abort( PortMidiStream* stream );
+     
+/**
+    Pm_Close() closes a midi stream, flushing any pending buffers.
+    (PortMidi attempts to close open streams when the application 
+    exits -- this is particularly difficult under Windows.)
+*/
+PMEXPORT PmError Pm_Close( PortMidiStream* stream );
+
+/**
+    Pm_Synchronize() instructs PortMidi to (re)synchronize to the
+    time_proc passed when the stream was opened. Typically, this
+    is used when the stream must be opened before the time_proc
+    reference is actually advancing. In this case, message timing
+    may be erratic, but since timestamps of zero mean 
+    "send immediately," initialization messages with zero timestamps
+    can be written without a functioning time reference and without
+    problems. Before the first MIDI message with a non-zero
+    timestamp is written to the stream, the time reference must
+    begin to advance (for example, if the time_proc computes time
+    based on audio samples, time might begin to advance when an 
+    audio stream becomes active). After time_proc return values
+    become valid, and BEFORE writing the first non-zero timestamped 
+    MIDI message, call Pm_Synchronize() so that PortMidi can observe
+    the difference between the current time_proc value and its
+    MIDI stream time. 
+    
+    In the more normal case where time_proc 
+    values advance continuously, there is no need to call 
+    Pm_Synchronize. PortMidi will always synchronize at the 
+    first output message and periodically thereafter.
+*/
+PmError Pm_Synchronize( PortMidiStream* stream );
+
+
+/**
+    Pm_Message() encodes a short Midi message into a 32-bit word. If data1
+    and/or data2 are not present, use zero.
+
+    Pm_MessageStatus(), Pm_MessageData1(), and 
+    Pm_MessageData2() extract fields from a 32-bit midi message.
+*/
+#define Pm_Message(status, data1, data2) \
+         ((((data2) << 16) & 0xFF0000) | \
+          (((data1) << 8) & 0xFF00) | \
+          ((status) & 0xFF))
+#define Pm_MessageStatus(msg) ((msg) & 0xFF)
+#define Pm_MessageData1(msg) (((msg) >> 8) & 0xFF)
+#define Pm_MessageData2(msg) (((msg) >> 16) & 0xFF)
+
+typedef int32_t PmMessage; /**< see PmEvent */
+/**
+   All midi data comes in the form of PmEvent structures. A sysex
+   message is encoded as a sequence of PmEvent structures, with each
+   structure carrying 4 bytes of the message, i.e. only the first
+   PmEvent carries the status byte.
+
+   Note that MIDI allows nested messages: the so-called "real-time" MIDI 
+   messages can be inserted into the MIDI byte stream at any location, 
+   including within a sysex message. MIDI real-time messages are one-byte
+   messages used mainly for timing (see the MIDI spec). PortMidi retains 
+   the order of non-real-time MIDI messages on both input and output, but 
+   it does not specify exactly how real-time messages are processed. This
+   is particulary problematic for MIDI input, because the input parser 
+   must either prepare to buffer an unlimited number of sysex message 
+   bytes or to buffer an unlimited number of real-time messages that 
+   arrive embedded in a long sysex message. To simplify things, the input
+   parser is allowed to pass real-time MIDI messages embedded within a 
+   sysex message, and it is up to the client to detect, process, and 
+   remove these messages as they arrive.
+
+   When receiving sysex messages, the sysex message is terminated
+   by either an EOX status byte (anywhere in the 4 byte messages) or
+   by a non-real-time status byte in the low order byte of the message.
+   If you get a non-real-time status byte but there was no EOX byte, it 
+   means the sysex message was somehow truncated. This is not
+   considered an error; e.g., a missing EOX can result from the user
+   disconnecting a MIDI cable during sysex transmission.
+
+   A real-time message can occur within a sysex message. A real-time 
+   message will always occupy a full PmEvent with the status byte in 
+   the low-order byte of the PmEvent message field. (This implies that
+   the byte-order of sysex bytes and real-time message bytes may not
+   be preserved -- for example, if a real-time message arrives after
+   3 bytes of a sysex message, the real-time message will be delivered
+   first. The first word of the sysex message will be delivered only
+   after the 4th byte arrives, filling the 4-byte PmEvent message field.
+   
+   The timestamp field is observed when the output port is opened with
+   a non-zero latency. A timestamp of zero means "use the current time",
+   which in turn means to deliver the message with a delay of
+   latency (the latency parameter used when opening the output port.)
+   Do not expect PortMidi to sort data according to timestamps -- 
+   messages should be sent in the correct order, and timestamps MUST 
+   be non-decreasing. See also "Example" for Pm_OpenOutput() above.
+
+   A sysex message will generally fill many PmEvent structures. On 
+   output to a PortMidiStream with non-zero latency, the first timestamp
+   on sysex message data will determine the time to begin sending the 
+   message. PortMidi implementations may ignore timestamps for the 
+   remainder of the sysex message. 
+   
+   On input, the timestamp ideally denotes the arrival time of the 
+   status byte of the message. The first timestamp on sysex message 
+   data will be valid. Subsequent timestamps may denote 
+   when message bytes were actually received, or they may be simply 
+   copies of the first timestamp.
+
+   Timestamps for nested messages: If a real-time message arrives in 
+   the middle of some other message, it is enqueued immediately with 
+   the timestamp corresponding to its arrival time. The interrupted 
+   non-real-time message or 4-byte packet of sysex data will be enqueued 
+   later. The timestamp of interrupted data will be equal to that of
+   the interrupting real-time message to insure that timestamps are
+   non-decreasing.
+ */
+typedef struct {
+    PmMessage      message;
+    PmTimestamp    timestamp;
+} PmEvent;
+
+/** 
+    @}
+*/
+/** \defgroup grp_io Reading and Writing Midi Messages
+    @{
+*/
+/**
+    Pm_Read() retrieves midi data into a buffer, and returns the number
+    of events read. Result is a non-negative number unless an error occurs, 
+    in which case a PmError value will be returned.
+
+    Buffer Overflow
+
+    The problem: if an input overflow occurs, data will be lost, ultimately 
+    because there is no flow control all the way back to the data source. 
+    When data is lost, the receiver should be notified and some sort of 
+    graceful recovery should take place, e.g. you shouldn't resume receiving 
+    in the middle of a long sysex message.
+
+    With a lock-free fifo, which is pretty much what we're stuck with to 
+    enable portability to the Mac, it's tricky for the producer and consumer 
+    to synchronously reset the buffer and resume normal operation.
+
+    Solution: the buffer managed by PortMidi will be flushed when an overflow
+    occurs. The consumer (Pm_Read()) gets an error message (pmBufferOverflow)
+    and ordinary processing resumes as soon as a new message arrives. The
+    remainder of a partial sysex message is not considered to be a "new
+    message" and will be flushed as well.
+
+*/
+PMEXPORT int Pm_Read( PortMidiStream *stream, PmEvent *buffer, int32_t length );
+
+/**
+    Pm_Poll() tests whether input is available, 
+    returning TRUE, FALSE, or an error value.
+*/
+PMEXPORT PmError Pm_Poll( PortMidiStream *stream);
+
+/** 
+    Pm_Write() writes midi data from a buffer. This may contain:
+        - short messages 
+    or 
+        - sysex messages that are converted into a sequence of PmEvent
+          structures, e.g. sending data from a file or forwarding them
+          from midi input.
+
+    Use Pm_WriteSysEx() to write a sysex message stored as a contiguous 
+    array of bytes.
+
+    Sysex data may contain embedded real-time messages.
+*/
+PMEXPORT PmError Pm_Write( PortMidiStream *stream, PmEvent *buffer, int32_t length );
+
+/**
+    Pm_WriteShort() writes a timestamped non-system-exclusive midi message.
+    Messages are delivered in order as received, and timestamps must be 
+    non-decreasing. (But timestamps are ignored if the stream was opened
+    with latency = 0.)
+*/
+PMEXPORT PmError Pm_WriteShort( PortMidiStream *stream, PmTimestamp when, int32_t msg);
+
+/**
+    Pm_WriteSysEx() writes a timestamped system-exclusive midi message.
+*/
+PMEXPORT PmError Pm_WriteSysEx( PortMidiStream *stream, PmTimestamp when, unsigned char *msg);
+
+/** @} */
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+#endif /* PORT_MIDI_H */