1 ZynAddSubFX Architecture
2 ========================
5 In order to understand how to effectively navigate the source code and to
6 better understand the relationships between the internal components of
8 To start off, the coarsest division of the codebase can be in breaking the
9 source into three areas:
12 Realtime Data and Audio/Midi Handling
14 Non-Realtime algorithms used to initialize realtime data and communication
17 Any User Interface (graphical or otherwise) that binds to a middleware
18 instance in order to permit modification of any parameters used in
21 These three components communicate to each other _almost_ exclusively through
22 the use of OSC messages using librtosc or liblo.
23 In this document, I hope to define all of the edge cases where communication
24 (by design) does not use message passing as interactions are somewhat
25 complicated lock free operations.
27 Before getting into each layer's details, the following threads may exist:
30 The original program thread, responsible for repeatedly polling events
31 from NSM, LASH, general in-process UI, and middleware
32 Middleware Helper Thread::
33 Responsible for handling any procedures which may block normal event
34 processing such as XML de-serialization
36 Thread responsible for performing synthesis and passing it to driver level
37 API for the sound to be output
39 Thread responsible for handling midi events. This thread is only active if
40 the audio output and the midi input drivers are not the same type.
42 Now for the meat of things:
47 Historically the realtime side of things has revolved around a single instance
48 of the aptly named class 'Master', which is the host to numerous
49 implementation pointers and instances of all Parts which in turn contain more
51 This instance generally assumes that it is in full control of all of its data
52 and it gets regularly called from the IO subsystem to produce some output
53 audio in increments of some set block size.
54 All classes that operate under a given instance of 'Master' assume that they
58 Unit of time to calculate at once and interval to perform interpolations
61 Size of the Additive Synthesis Oscillator Interpolation Buffer
63 Number of samples per second
65 Source for memory allocations from a resizable memory pool
67 Changing any of these essentially requires rebuilding all child data
68 structures at the moment.
70 Most of the children objects can be placed into the categories:
73 Objects which contain serialize able parameters for synthesis and little to
76 Objects which initialize with parameter objects and generate output audio or
77 control values for other synthesis objects
79 Objects which are responsible for organizing a dvariety of synthesis and
80 parameter objects and for routing the outputs of each child object to the
81 right destination (e.g. 'Part' and 'Master')
83 Objects which have _Odd_ divisions between what is a parameter, and what
84 is destined for synthesis (e.g. 'PADnoteParameters' and 'OscilGen')
86 The normal behavior of these objects can be seen by observing a call of
87 _OutMgr::tick_ which first flushes the midi queue possibly constructing a few
88 new notes via _Part::NoteOn_, then _Master::AudioOut_ is called.
89 This is the root of the synthesis calls, but before anything is synthesized,
90 OSC messages are dispatched which typically update system parameter and
91 coefficients which cannot be calculated in realtime such as padnote based
93 Most data is allocated on the initialization of the add/sub/pad synthesis
94 engine, however anything which cannot be bounded easily then is allocated via
95 the tlsf based allocator.
101 Now in the previous section, details on how exactly messages were delivered
102 was only vaguely mentioned.
103 Anything unclear should hopefully be clarified here.
104 The primary message handling is taken care of by two ring buffers 'uToB' and
105 'bToU' which are, respectively, the user interface to backend and the backend
106 to user interface ringbuffers.
107 Additionally, Middleware handles non-realtime processing, such as 'Oscilgen'
108 and 'PADnoteParameters'.
110 To handle these cases, any message from a user interface is intercepted.
111 Non-realtime requests are handled in middleware itself and other messages are
113 This permits some internal messages to be sent that the UI has never directly
115 A similar process occurs for messages originating from the backend.
117 A large portion of the middleware code is designed to manage up-to-date
118 pointers to the internal datastructures, in order to avoid directly accessing
119 anything via the pointer to the 'Master' datastructure.
124 In order to avoid access to the backend datastructures typically a replacement
125 object is sent to the backend to be copied from or from which a pointer swap
131 This is where the nice pristine hands off approach sadly comes to an end.
132 There simply isn't an effective means of capturing all parameters without
133 taking a large amount of time.
135 The master has two kinds of parameter objects:
136 - Realtime parameters which are only ever mutable through
137 * OSC dispatch within Master
138 - Non realtime parameters which are only ever mutable through
139 * OSC dispatch within Master
140 * MiddleWare (using struct NonRtObjStore)
141 Now, in order to permit the serialization of parameter objects, the backend is
142 'frozen': Since the freezing message is the last one the MiddleWare
143 sends, this essentially prevents the backend from processing further messages
144 from the user interface. When this occurs the parameters which are to be
145 serialized can be guaranteed to be constant and thus safe to access across
148 This class of read-only-operation can be seen as used in parameter copy/paste
149 operations and in saving full instances as well as instruments.
155 From an architectural standpoint the important thing to note about the user
156 interface is that virtual every widget has a location which is composed of a
157 base path and a path extension.
158 Most messages going to a widget are solely to this widget's one location
159 (occasionally they're to a few associated paths).
161 This structure makes it possible for a set of widgets to get relocated
162 (rebase/reext) to another path.
163 This occurs quite frequently (e.g. "/part0/PVolume" -> "/part1/PVolume") and
164 it may be the occasional source of bugs.