2 Copyright (C) 2013 Paul Davis
4 This program is free software; you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; either version 2 of the License, or
7 (at your option) any later version.
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
14 You should have received a copy of the GNU General Public License
15 along with this program; if not, write to the Free Software
16 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
20 #ifndef __libardour_audiobackend_h__
21 #define __libardour_audiobackend_h__
29 #include <boost/function.hpp>
31 #include "ardour/libardour_visibility.h"
32 #include "ardour/types.h"
33 #include "ardour/audioengine.h"
34 #include "ardour/port_engine.h"
36 #ifdef ARDOURBACKEND_DLL_EXPORTS // defined if we are building the ARDOUR Panners DLLs (instead of using them)
37 #define ARDOURBACKEND_API LIBARDOUR_DLL_EXPORT
39 #define ARDOURBACKEND_API LIBARDOUR_DLL_IMPORT
41 #define ARDOURBACKEND_LOCAL LIBARDOUR_DLL_LOCAL
45 class LIBARDOUR_API AudioBackend : public PortEngine {
48 AudioBackend (AudioEngine& e) : PortEngine (e), engine (e) {}
49 virtual ~AudioBackend () {}
51 /** Return the name of this backend.
53 * Should use a well-known, unique term. Expected examples
54 * might include "JACK", "CoreAudio", "ASIO" etc.
56 virtual std::string name() const = 0;
58 /** Return true if the callback from the underlying mechanism/API
59 * (CoreAudio, JACK, ASIO etc.) occurs in a thread subject to realtime
60 * constraints. Return false otherwise.
62 virtual bool is_realtime () const = 0;
64 /* Discovering devices and parameters */
66 /** Return true if this backend requires the selection of a "driver"
67 * before any device can be selected. Return false otherwise.
69 * Intended mainly to differentiate between meta-APIs like JACK
70 * which can still expose different backends (such as ALSA or CoreAudio
71 * or FFADO or netjack) and those like ASIO or CoreAudio which
74 virtual bool requires_driver_selection() const { return false; }
76 /** If the return value of requires_driver_selection() is true,
77 * then this function can return the list of known driver names.
79 * If the return value of requires_driver_selection() is false,
80 * then this function should not be called. If it is called
81 * its return value is an empty vector of strings.
83 virtual std::vector<std::string> enumerate_drivers() const { return std::vector<std::string>(); }
85 /** Returns zero if the backend can successfully use @param name as the
86 * driver, non-zero otherwise.
88 * Should not be used unless the backend returns true from
89 * requires_driver_selection()
91 virtual int set_driver (const std::string& /*drivername*/) { return 0; }
93 /** used to list device names along with whether or not they are currently
100 DeviceStatus (const std::string& s, bool avail) : name (s), available (avail) {}
103 /** Returns a collection of DeviceStatuses identifying devices discovered
104 * by this backend since the start of the process.
106 * Any of the names in each DeviceStatus may be used to identify a
107 * device in other calls to the backend, though any of them may become
108 * invalid at any time.
110 virtual std::vector<DeviceStatus> enumerate_devices () const = 0;
112 /** Returns a collection of float identifying sample rates that are
113 * potentially usable with the hardware identified by @param device.
114 * Any of these values may be supplied in other calls to this backend
115 * as the desired sample rate to use with the name device, but the
116 * requested sample rate may turn out to be unavailable, or become invalid
119 virtual std::vector<float> available_sample_rates (const std::string& device) const = 0;
121 /* Returns the default sample rate that will be shown to the user when
122 * configuration options are first presented. If the derived class
123 * needs or wants to override this, it can. It also MUST override this
124 * if there is any chance that an SR of 44.1kHz is not in the list
125 * returned by available_sample_rates()
127 virtual float default_sample_rate () const {
131 /** Returns a collection of uint32 identifying buffer sizes that are
132 * potentially usable with the hardware identified by @param device.
133 * Any of these values may be supplied in other calls to this backend
134 * as the desired buffer size to use with the name device, but the
135 * requested buffer size may turn out to be unavailable, or become invalid
138 virtual std::vector<uint32_t> available_buffer_sizes (const std::string& device) const = 0;
140 /* Returns the default buffer size that will be shown to the user when
141 * configuration options are first presented. If the derived class
142 * needs or wants to override this, it can. It also MUST override this
143 * if there is any chance that a buffer size of 1024 is not in the list
144 * returned by available_buffer_sizes()
146 virtual uint32_t default_buffer_size () const {
150 /** Returns the maximum number of input channels that are potentially
151 * usable with the hardware identified by @param device. Any number from 1
152 * to the value returned may be supplied in other calls to this backend as
153 * the input channel count to use with the name device, but the requested
154 * count may turn out to be unavailable, or become invalid at any time.
156 virtual uint32_t available_input_channel_count (const std::string& device) const = 0;
158 /** Returns the maximum number of output channels that are potentially
159 * usable with the hardware identified by @param device. Any number from 1
160 * to the value returned may be supplied in other calls to this backend as
161 * the output channel count to use with the name device, but the requested
162 * count may turn out to be unavailable, or become invalid at any time.
164 virtual uint32_t available_output_channel_count (const std::string& device) const = 0;
166 /* Return true if the derived class can change the sample rate of the
167 * device in use while the device is already being used. Return false
168 * otherwise. (example: JACK cannot do this as of September 2013)
170 virtual bool can_change_sample_rate_when_running () const = 0;
171 /* Return true if the derived class can change the buffer size of the
172 * device in use while the device is already being used. Return false
175 virtual bool can_change_buffer_size_when_running () const = 0;
177 /* Set the hardware parameters.
179 * If called when the current state is stopped or paused,
180 * the changes will not take effect until the state changes to running.
182 * If called while running, the state will change as fast as the
183 * implementation allows.
185 * All set_*() methods return zero on success, non-zero otherwise.
188 /** Set the name of the device to be used
190 virtual int set_device_name (const std::string&) = 0;
191 /** Set the sample rate to be used
193 virtual int set_sample_rate (float) = 0;
194 /** Set the buffer size to be used.
196 * The device is assumed to use a double buffering scheme, so that one
197 * buffer's worth of data can be processed by hardware while software works
198 * on the other buffer. All known suitable audio APIs support this model
199 * (though ALSA allows for alternate numbers of buffers, and CoreAudio
200 * doesn't directly expose the concept).
202 virtual int set_buffer_size (uint32_t) = 0;
203 /** Set the preferred underlying hardware sample format
205 * This does not change the sample format (32 bit float) read and
206 * written to the device via the Port API.
208 virtual int set_sample_format (SampleFormat) = 0;
209 /** Set the preferred underlying hardware data layout.
210 * If @param yn is true, then the hardware will interleave
211 * samples for successive channels; otherwise, the hardware will store
212 * samples for a single channel contiguously.
214 * Setting this does not change the fact that all data streams
215 * to and from Ports are mono (essentially, non-interleaved)
217 virtual int set_interleaved (bool yn) = 0;
218 /** Set the number of input channels that should be used
220 virtual int set_input_channels (uint32_t) = 0;
221 /** Set the number of output channels that should be used
223 virtual int set_output_channels (uint32_t) = 0;
224 /** Set the (additional) input latency that cannot be determined via
225 * the implementation's underlying code (e.g. latency from
226 * external D-A/D-A converters. Units are samples.
228 virtual int set_systemic_input_latency (uint32_t) = 0;
229 /** Set the (additional) output latency that cannot be determined via
230 * the implementation's underlying code (e.g. latency from
231 * external D-A/D-A converters. Units are samples.
233 virtual int set_systemic_output_latency (uint32_t) = 0;
235 /* Retrieving parameters */
237 virtual std::string device_name () const = 0;
238 virtual float sample_rate () const = 0;
239 virtual uint32_t buffer_size () const = 0;
240 virtual SampleFormat sample_format () const = 0;
241 virtual bool interleaved () const = 0;
242 virtual uint32_t input_channels () const = 0;
243 virtual uint32_t output_channels () const = 0;
244 virtual uint32_t systemic_input_latency () const = 0;
245 virtual uint32_t systemic_output_latency () const = 0;
247 /** override this if this implementation returns true from
248 * requires_driver_selection()
250 virtual std::string driver_name() const { return std::string(); }
252 /** Return the name of a control application for the
253 * selected/in-use device. If no such application exists,
254 * or if no device has been selected or is in-use,
255 * return an empty string.
257 virtual std::string control_app_name() const = 0;
258 /** Launch the control app for the currently in-use or
259 * selected device. May do nothing if the control
260 * app is undefined or cannot be launched.
262 virtual void launch_control_app () = 0;
264 /* @return a vector of strings that describe the available
267 * These can be presented to the user to decide which
268 * MIDI drivers, options etc. can be used. The returned strings
269 * should be thought of as the key to a map of possible
270 * approaches to handling MIDI within the backend. Ensure that
271 * the strings will make sense to the user.
273 virtual std::vector<std::string> enumerate_midi_options () const = 0;
275 /* Request the use of the MIDI option named @param option, which
276 * should be one of the strings returned by enumerate_midi_options()
278 * @return zero if successful, non-zero otherwise
280 virtual int set_midi_option (const std::string& option) = 0;
282 virtual std::string midi_option () const = 0;
286 /** Start using the device named in the most recent call
287 * to set_device(), with the parameters set by various
288 * the most recent calls to set_sample_rate() etc. etc.
290 * At some undetermined time after this function is successfully called,
291 * the backend will start calling the ::process_callback() method of
292 * the AudioEngine referenced by @param engine. These calls will
293 * occur in a thread created by and/or under the control of the backend.
295 * @param for_latency_measurement if true, the device is being started
296 * to carry out latency measurements and the backend should this
297 * take care to return latency numbers that do not reflect
298 * any existing systemic latency settings.
300 * Return zero if successful, negative values otherwise.
305 * Why is this non-virtual but ::_start() is virtual ?
306 * Virtual methods with default parameters create possible ambiguity
307 * because a derived class may implement the same method with a different
308 * type or value of default parameter.
310 * So we make this non-virtual method to avoid possible overrides of
311 * default parameters. See Scott Meyers or other books on C++ to understand
312 * this pattern, or possibly just this:
314 * http://stackoverflow.com/questions/12139786/good-pratice-default-arguments-for-pure-virtual-method
316 int start (bool for_latency_measurement=false) {
317 return _start (for_latency_measurement);
320 /** Stop using the device currently in use.
322 * If the function is successfully called, no subsequent calls to the
323 * process_callback() of @param engine will be made after the function
324 * returns, until parameters are reset and start() are called again.
326 * The backend is considered to be un-configured after a successful
327 * return, and requires calls to set hardware parameters before it can be
328 * start()-ed again. See pause() for a way to avoid this. stop() should
329 * only be used when reconfiguration is required OR when there are no
330 * plans to use the backend in the future with a reconfiguration.
332 * Return zero if successful, 1 if the device is not in use, negative values on error
334 virtual int stop () = 0;
336 /** While remaining connected to the device, and without changing its
337 * configuration, start (or stop) calling the process_callback() of @param engine
338 * without waiting for the device. Once process_callback() has returned, it
339 * will be called again immediately, thus allowing for faster-than-realtime
342 * All registered ports remain in existence and all connections remain
343 * unaltered. However, any physical ports should NOT be used by the
344 * process_callback() during freewheeling - the data behaviour is undefined.
346 * If @param start_stop is true, begin this behaviour; otherwise cease this
347 * behaviour if it currently occuring, and return to calling
348 * process_callback() of @param engine by waiting for the device.
350 * Return zero on success, non-zero otherwise.
352 virtual int freewheel (bool start_stop) = 0;
354 /** return the fraction of the time represented by the current buffer
355 * size that is being used for each buffer process cycle, as a value
358 * E.g. if the buffer size represents 5msec and current processing
359 * takes 1msec, the returned value should be 0.2.
361 * Implementations can feel free to smooth the values returned over
362 * time (e.g. high pass filtering, or its equivalent).
364 virtual float dsp_load() const = 0;
366 /* Transport Control (JACK is the only audio API that currently offers
367 the concept of shared transport control)
370 /** Attempt to change the transport state to TransportRolling.
372 virtual void transport_start () {}
373 /** Attempt to change the transport state to TransportStopped.
375 virtual void transport_stop () {}
376 /** return the current transport state
378 virtual TransportState transport_state () const { return TransportStopped; }
379 /** Attempt to locate the transport to @param pos
381 virtual void transport_locate (framepos_t /*pos*/) {}
382 /** Return the current transport location, in samples measured
383 * from the origin (defined by the transport time master)
385 virtual framepos_t transport_frame() const { return 0; }
387 /** If @param yn is true, become the time master for any inter-application transport
388 * timebase, otherwise cease to be the time master for the same.
390 * Return zero on success, non-zero otherwise
392 * JACK is the only currently known audio API with the concept of a shared
393 * transport timebase.
395 virtual int set_time_master (bool /*yn*/) { return 0; }
397 virtual int usecs_per_cycle () const { return 1000000 * (buffer_size() / sample_rate()); }
398 virtual size_t raw_buffer_size (DataType t) = 0;
402 /** return the time according to the sample clock in use, measured in
403 * samples since an arbitrary zero time in the past. The value should
404 * increase monotonically and linearly, without interruption from any
405 * source (including CPU frequency scaling).
407 * It is extremely likely that any implementation will use a DLL, since
408 * this function can be called from any thread, at any time, and must be
409 * able to accurately determine the correct sample time.
411 * Can be called from any thread.
413 virtual pframes_t sample_time () = 0;
415 /** Return the time according to the sample clock in use when the most
416 * recent buffer process cycle began. Can be called from any thread.
418 virtual pframes_t sample_time_at_cycle_start () = 0;
420 /** Return the time since the current buffer process cycle started,
421 * in samples, according to the sample clock in use.
423 * Can ONLY be called from within a process() callback tree (which
424 * implies that it can only be called by a process thread)
426 virtual pframes_t samples_since_cycle_start () = 0;
428 /** Return true if it possible to determine the offset in samples of the
429 * first video frame that starts within the current buffer process cycle,
430 * measured from the first sample of the cycle. If returning true,
431 * set @param offset to that offset.
433 * Eg. if it can be determined that the first video frame within the cycle
434 * starts 28 samples after the first sample of the cycle, then this method
435 * should return true and set @param offset to 28.
437 * May be impossible to support outside of JACK, which has specific support
438 * (in some cases, hardware support) for this feature.
440 * Can ONLY be called from within a process() callback tree (which implies
441 * that it can only be called by a process thread)
443 virtual bool get_sync_offset (pframes_t& /*offset*/) const { return false; }
445 /** Create a new thread suitable for running part of the buffer process
446 * cycle (i.e. Realtime scheduling, memory allocation, etc. etc are all
447 * correctly setup), with a stack size given in bytes by specified @param
448 * stacksize. The thread will begin executing @param func, and will exit
449 * when that function returns.
451 virtual int create_process_thread (boost::function<void()> func) = 0;
453 /** Wait for all processing threads to exit.
455 * Return zero on success, non-zero on failure.
457 virtual int join_process_threads () = 0;
459 /** Return true if execution context is in a backend thread
461 virtual bool in_process_thread () = 0;
463 /** Return the minimum stack size of audio threads in bytes
465 static size_t thread_stack_size () { return 100000; }
467 /** Return number of processing threads
469 virtual uint32_t process_thread_count () = 0;
471 virtual void update_latencies () = 0;
473 /** Set @param speed and @param position to the current speed and position
474 * indicated by some transport sync signal. Return whether the current
475 * transport state is pending, or finalized.
477 * Derived classes only need implement this if they provide some way to
478 * sync to a transport sync signal (e.g. Sony 9 Pin) that is not
479 * handled by Ardour itself (LTC and MTC are both handled by Ardour).
480 * The canonical example is JACK Transport.
482 virtual bool speed_and_position (double& speed, framepos_t& position) {
491 virtual int _start (bool for_latency_measurement) = 0;
494 struct LIBARDOUR_API AudioBackendInfo {
497 /** Using arg1 and arg2, initialize this audiobackend.
499 * Returns zero on success, non-zero otherwise.
501 int (*instantiate) (const std::string& arg1, const std::string& arg2);
503 /** Release all resources associated with this audiobackend
505 int (*deinstantiate) (void);
507 /** Factory method to create an AudioBackend-derived class.
509 * Returns a valid shared_ptr to the object if successfull,
510 * or a "null" shared_ptr otherwise.
512 boost::shared_ptr<AudioBackend> (*factory) (AudioEngine&);
514 /** Return true if the underlying mechanism/API has been
515 * configured and does not need (re)configuration in order
516 * to be usable. Return false otherwise.
518 * Note that this may return true if (re)configuration, even though
519 * not currently required, is still possible.
521 bool (*already_configured)();
526 #endif /* __libardour_audiobackend_h__ */