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85 lines
3.6 KiB
Plaintext
85 lines
3.6 KiB
Plaintext
README for PortMidi
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Roger B. Dannenberg
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VERSION: please use "svn info" to get info.
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Documentation for PortMidi is found in pm_common/portmidi.h.
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Additional documentation:
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- Windows: see pm_win/README_WIN.txt and pm_win/debugging_dlls.txt
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- Linux: see pm_linux/README_LINUX.txt
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- Mac OSX: see pm_mac/README_MAC.txt
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- Common Lisp: see pm_cl/README_CL.txt
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- Eclipse: see portmidi_cdt.zip (this was contributed as is; the dlls here
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are now -- Sep 09 -- out of date. What is really needed is a script
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to generate this release automatically so we can maintain it.)
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- C-Sharp: see pm_csharp.zip (also contributed as is)
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---------- some notes on the design of PortMidi ----------
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POINTERS VS DEVICE NUMBERS
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When you open a MIDI port, PortMidi allocates a structure to
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maintain the state of the open device. Since every device is
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also listed in a table, you might think it would be simpler to
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use the table index rather than a pointer to identify a device.
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This would also help with error checking (it's hard to make
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sure a pointer is valid). PortMidi's design parallels that of
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PortAudio.
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ERROR HANDLING
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Error handling turned out to be much more complicated than expected.
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PortMidi functions return error codes that the caller can check.
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In addition, errors may occur asynchronously due to MIDI input.
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However, for Windows, there are virtually no errors that can
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occur if the code is correct and not passing bogus values. One
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exception is an error that the system is out of memory, but my
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guess is that one is unlikely to recover gracefully from that.
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Therefore, all errors in callbacks are guarded by assert(), which
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means not guarded at all in release configurations.
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Ordinarily, the caller checks for an error code. If the error is
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system-dependent, pmHostError is returned and the caller can
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call Pm_GetHostErrorText to get a text description of the error.
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Host error codes are system-specific and are recorded in the
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system-specific data allocated for each open MIDI port.
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However, if an error occurs on open or close,
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we cannot store the error with the device because there will be
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no device data (assuming PortMidi cleans up after devices that
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are not open). For open and close, we will convert the error
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to text, copy it to a global string, and set pm_hosterror, a
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global flag.
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Similarly, whenever a Read or Write operation returns pmHostError,
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the corresponding error string is copied to a global string
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and pm_hosterror is set. This makes getting error strings
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simple and uniform, although it does cost a string copy and some
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overhead even if the user does not want to look at the error data.
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The system-specific Read, Write, Poll, etc. implementations should
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check for asynchronous errors and return immediately if one is
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found so that these get reported. This happens in the Mac OS X
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code, where lots of things are happening in callbacks, but again,
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in Windows, there are no error codes recorded in callbacks.
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DEBUGGING
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If you are building a console application for research, we suggest
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compiling with the option PM_CHECK_ERRORS. This will insert a
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check for error return values at the end of each PortMidi
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function. If an error is encountered, a text message is printed
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using printf(), the user is asked to type ENTER, and then exit(-1)
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is called to clean up and terminate the program.
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You should not use PM_CHECK_ERRORS if printf() does not work
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(e.g. this is not a console application under Windows, or there
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is no visible console on some other OS), and you should not use
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PM_CHECK_ERRORS if you intend to recover from errors rather than
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abruptly terminate the program.
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The Windows version (and perhaps others) also offers a DEBUG
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compile-time option. See README_WIN.txt.
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