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"
35 #include "ardour/visibility.h"
37 #ifdef ARDOURBACKEND_DLL_EXPORTS // defined if we are building the ARDOUR Panners DLLs (instead of using them)
38 #define ARDOURBACKEND_API LIBARDOUR_HELPER_DLL_EXPORT
40 #define ARDOURBACKEND_API LIBARDOUR_HELPER_DLL_IMPORT
42 #define ARDOURBACKEND_LOCAL LIBARDOUR_HELPER_DLL_LOCAL
46 class LIBARDOUR_API AudioBackend : public PortEngine {
49 AudioBackend (AudioEngine& e) : PortEngine (e), engine (e) {}
50 virtual ~AudioBackend () {}
52 /** Return the name of this backend.
54 * Should use a well-known, unique term. Expected examples
55 * might include "JACK", "CoreAudio", "ASIO" etc.
57 virtual std::string name() const = 0;
59 /** Return true if the callback from the underlying mechanism/API
60 * (CoreAudio, JACK, ASIO etc.) occurs in a thread subject to realtime
61 * constraints. Return false otherwise.
63 virtual bool is_realtime () const = 0;
65 /* Discovering devices and parameters */
67 /** Return true if this backend requires the selection of a "driver"
68 * before any device can be selected. Return false otherwise.
70 * Intended mainly to differentiate between meta-APIs like JACK
71 * which can still expose different backends (such as ALSA or CoreAudio
72 * or FFADO or netjack) and those like ASIO or CoreAudio which
75 virtual bool requires_driver_selection() const { return false; }
77 /** If the return value of requires_driver_selection() is true,
78 * then this function can return the list of known driver names.
80 * If the return value of requires_driver_selection() is false,
81 * then this function should not be called. If it is called
82 * its return value is an empty vector of strings.
84 virtual std::vector<std::string> enumerate_drivers() const { return std::vector<std::string>(); }
86 /** Returns zero if the backend can successfully use @param name as the
87 * driver, non-zero otherwise.
89 * Should not be used unless the backend returns true from
90 * requires_driver_selection()
92 virtual int set_driver (const std::string& /*drivername*/) { return 0; }
94 /** used to list device names along with whether or not they are currently
101 DeviceStatus (const std::string& s, bool avail) : name (s), available (avail) {}
104 /** Returns a collection of DeviceStatuses identifying devices discovered
105 * by this backend since the start of the process.
107 * Any of the names in each DeviceStatus may be used to identify a
108 * device in other calls to the backend, though any of them may become
109 * invalid at any time.
111 virtual std::vector<DeviceStatus> enumerate_devices () const = 0;
113 /** Returns a collection of float identifying sample rates that are
114 * potentially usable with the hardware identified by @param device.
115 * Any of these values may be supplied in other calls to this backend
116 * as the desired sample rate to use with the name device, but the
117 * requested sample rate may turn out to be unavailable, or become invalid
120 virtual std::vector<float> available_sample_rates (const std::string& device) const = 0;
122 /* Returns the default sample rate that will be shown to the user when
123 * configuration options are first presented. If the derived class
124 * needs or wants to override this, it can. It also MUST override this
125 * if there is any chance that an SR of 44.1kHz is not in the list
126 * returned by available_sample_rates()
128 virtual float default_sample_rate () const {
132 /** Returns a collection of uint32 identifying buffer sizes that are
133 * potentially usable with the hardware identified by @param device.
134 * Any of these values may be supplied in other calls to this backend
135 * as the desired buffer size to use with the name device, but the
136 * requested buffer size may turn out to be unavailable, or become invalid
139 virtual std::vector<uint32_t> available_buffer_sizes (const std::string& device) const = 0;
141 /* Returns the default buffer size that will be shown to the user when
142 * configuration options are first presented. If the derived class
143 * needs or wants to override this, it can. It also MUST override this
144 * if there is any chance that a buffer size of 1024 is not in the list
145 * returned by available_buffer_sizes()
147 virtual uint32_t default_buffer_size () const {
151 /** Returns the maximum number of input channels that are potentially
152 * usable with the hardware identified by @param device. Any number from 1
153 * to the value returned may be supplied in other calls to this backend as
154 * the input channel count to use with the name device, but the requested
155 * count may turn out to be unavailable, or become invalid at any time.
157 virtual uint32_t available_input_channel_count (const std::string& device) const = 0;
159 /** Returns the maximum number of output channels that are potentially
160 * usable with the hardware identified by @param device. Any number from 1
161 * to the value returned may be supplied in other calls to this backend as
162 * the output channel count to use with the name device, but the requested
163 * count may turn out to be unavailable, or become invalid at any time.
165 virtual uint32_t available_output_channel_count (const std::string& device) const = 0;
167 /* Return true if the derived class can change the sample rate of the
168 * device in use while the device is already being used. Return false
169 * otherwise. (example: JACK cannot do this as of September 2013)
171 virtual bool can_change_sample_rate_when_running () const = 0;
172 /* Return true if the derived class can change the buffer size of the
173 * device in use while the device is already being used. Return false
176 virtual bool can_change_buffer_size_when_running () const = 0;
178 /* Set the hardware parameters.
180 * If called when the current state is stopped or paused,
181 * the changes will not take effect until the state changes to running.
183 * If called while running, the state will change as fast as the
184 * implementation allows.
186 * All set_*() methods return zero on success, non-zero otherwise.
189 /** Set the name of the device to be used
191 virtual int set_device_name (const std::string&) = 0;
192 /** Set the sample rate to be used
194 virtual int set_sample_rate (float) = 0;
195 /** Set the buffer size to be used.
197 * The device is assumed to use a double buffering scheme, so that one
198 * buffer's worth of data can be processed by hardware while software works
199 * on the other buffer. All known suitable audio APIs support this model
200 * (though ALSA allows for alternate numbers of buffers, and CoreAudio
201 * doesn't directly expose the concept).
203 virtual int set_buffer_size (uint32_t) = 0;
204 /** Set the preferred underlying hardware sample format
206 * This does not change the sample format (32 bit float) read and
207 * written to the device via the Port API.
209 virtual int set_sample_format (SampleFormat) = 0;
210 /** Set the preferred underlying hardware data layout.
211 * If @param yn is true, then the hardware will interleave
212 * samples for successive channels; otherwise, the hardware will store
213 * samples for a single channel contiguously.
215 * Setting this does not change the fact that all data streams
216 * to and from Ports are mono (essentially, non-interleaved)
218 virtual int set_interleaved (bool yn) = 0;
219 /** Set the number of input channels that should be used
221 virtual int set_input_channels (uint32_t) = 0;
222 /** Set the number of output channels that should be used
224 virtual int set_output_channels (uint32_t) = 0;
225 /** Set the (additional) input latency that cannot be determined via
226 * the implementation's underlying code (e.g. latency from
227 * external D-A/D-A converters. Units are samples.
229 virtual int set_systemic_input_latency (uint32_t) = 0;
230 /** Set the (additional) output latency that cannot be determined via
231 * the implementation's underlying code (e.g. latency from
232 * external D-A/D-A converters. Units are samples.
234 virtual int set_systemic_output_latency (uint32_t) = 0;
236 /* Retrieving parameters */
238 virtual std::string device_name () const = 0;
239 virtual float sample_rate () const = 0;
240 virtual uint32_t buffer_size () const = 0;
241 virtual SampleFormat sample_format () const = 0;
242 virtual bool interleaved () const = 0;
243 virtual uint32_t input_channels () const = 0;
244 virtual uint32_t output_channels () const = 0;
245 virtual uint32_t systemic_input_latency () const = 0;
246 virtual uint32_t systemic_output_latency () const = 0;
248 /** override this if this implementation returns true from
249 * requires_driver_selection()
251 virtual std::string driver_name() const { return std::string(); }
253 /** Return the name of a control application for the
254 * selected/in-use device. If no such application exists,
255 * or if no device has been selected or is in-use,
256 * return an empty string.
258 virtual std::string control_app_name() const = 0;
259 /** Launch the control app for the currently in-use or
260 * selected device. May do nothing if the control
261 * app is undefined or cannot be launched.
263 virtual void launch_control_app () = 0;
265 /* @return a vector of strings that describe the available
268 * These can be presented to the user to decide which
269 * MIDI drivers, options etc. can be used. The returned strings
270 * should be thought of as the key to a map of possible
271 * approaches to handling MIDI within the backend. Ensure that
272 * the strings will make sense to the user.
274 virtual std::vector<std::string> enumerate_midi_options () const = 0;
276 /* Request the use of the MIDI option named @param option, which
277 * should be one of the strings returned by enumerate_midi_options()
279 * @return zero if successful, non-zero otherwise
281 virtual int set_midi_option (const std::string& option) = 0;
283 virtual std::string midi_option () const = 0;
287 /** Start using the device named in the most recent call
288 * to set_device(), with the parameters set by various
289 * the most recent calls to set_sample_rate() etc. etc.
291 * At some undetermined time after this function is successfully called,
292 * the backend will start calling the ::process_callback() method of
293 * the AudioEngine referenced by @param engine. These calls will
294 * occur in a thread created by and/or under the control of the backend.
296 * @param for_latency_measurement if true, the device is being started
297 * to carry out latency measurements and the backend should this
298 * take care to return latency numbers that do not reflect
299 * any existing systemic latency settings.
301 * Return zero if successful, negative values otherwise.
306 * Why is this non-virtual but ::_start() is virtual ?
307 * Virtual methods with default parameters create possible ambiguity
308 * because a derived class may implement the same method with a different
309 * type or value of default parameter.
311 * So we make this non-virtual method to avoid possible overrides of
312 * default parameters. See Scott Meyers or other books on C++ to understand
313 * this pattern, or possibly just this:
315 * http://stackoverflow.com/questions/12139786/good-pratice-default-arguments-for-pure-virtual-method
317 int start (bool for_latency_measurement=false) {
318 return _start (for_latency_measurement);
321 /** Stop using the device currently in use.
323 * If the function is successfully called, no subsequent calls to the
324 * process_callback() of @param engine will be made after the function
325 * returns, until parameters are reset and start() are called again.
327 * The backend is considered to be un-configured after a successful
328 * return, and requires calls to set hardware parameters before it can be
329 * start()-ed again. See pause() for a way to avoid this. stop() should
330 * only be used when reconfiguration is required OR when there are no
331 * plans to use the backend in the future with a reconfiguration.
333 * Return zero if successful, 1 if the device is not in use, negative values on error
335 virtual int stop () = 0;
337 /** While remaining connected to the device, and without changing its
338 * configuration, start (or stop) calling the process_callback() of @param engine
339 * without waiting for the device. Once process_callback() has returned, it
340 * will be called again immediately, thus allowing for faster-than-realtime
343 * All registered ports remain in existence and all connections remain
344 * unaltered. However, any physical ports should NOT be used by the
345 * process_callback() during freewheeling - the data behaviour is undefined.
347 * If @param start_stop is true, begin this behaviour; otherwise cease this
348 * behaviour if it currently occuring, and return to calling
349 * process_callback() of @param engine by waiting for the device.
351 * Return zero on success, non-zero otherwise.
353 virtual int freewheel (bool start_stop) = 0;
355 /** return the fraction of the time represented by the current buffer
356 * size that is being used for each buffer process cycle, as a value
359 * E.g. if the buffer size represents 5msec and current processing
360 * takes 1msec, the returned value should be 0.2.
362 * Implementations can feel free to smooth the values returned over
363 * time (e.g. high pass filtering, or its equivalent).
365 virtual float dsp_load() const = 0;
367 /* Transport Control (JACK is the only audio API that currently offers
368 the concept of shared transport control)
371 /** Attempt to change the transport state to TransportRolling.
373 virtual void transport_start () {}
374 /** Attempt to change the transport state to TransportStopped.
376 virtual void transport_stop () {}
377 /** return the current transport state
379 virtual TransportState transport_state () const { return TransportStopped; }
380 /** Attempt to locate the transport to @param pos
382 virtual void transport_locate (framepos_t /*pos*/) {}
383 /** Return the current transport location, in samples measured
384 * from the origin (defined by the transport time master)
386 virtual framepos_t transport_frame() const { return 0; }
388 /** If @param yn is true, become the time master for any inter-application transport
389 * timebase, otherwise cease to be the time master for the same.
391 * Return zero on success, non-zero otherwise
393 * JACK is the only currently known audio API with the concept of a shared
394 * transport timebase.
396 virtual int set_time_master (bool /*yn*/) { return 0; }
398 virtual int usecs_per_cycle () const { return 1000000 * (buffer_size() / sample_rate()); }
399 virtual size_t raw_buffer_size (DataType t) = 0;
403 /** return the time according to the sample clock in use, measured in
404 * samples since an arbitrary zero time in the past. The value should
405 * increase monotonically and linearly, without interruption from any
406 * source (including CPU frequency scaling).
408 * It is extremely likely that any implementation will use a DLL, since
409 * this function can be called from any thread, at any time, and must be
410 * able to accurately determine the correct sample time.
412 * Can be called from any thread.
414 virtual pframes_t sample_time () = 0;
416 /** Return the time according to the sample clock in use when the most
417 * recent buffer process cycle began. Can be called from any thread.
419 virtual pframes_t sample_time_at_cycle_start () = 0;
421 /** Return the time since the current buffer process cycle started,
422 * in samples, according to the sample clock in use.
424 * Can ONLY be called from within a process() callback tree (which
425 * implies that it can only be called by a process thread)
427 virtual pframes_t samples_since_cycle_start () = 0;
429 /** Return true if it possible to determine the offset in samples of the
430 * first video frame that starts within the current buffer process cycle,
431 * measured from the first sample of the cycle. If returning true,
432 * set @param offset to that offset.
434 * Eg. if it can be determined that the first video frame within the cycle
435 * starts 28 samples after the first sample of the cycle, then this method
436 * should return true and set @param offset to 28.
438 * May be impossible to support outside of JACK, which has specific support
439 * (in some cases, hardware support) for this feature.
441 * Can ONLY be called from within a process() callback tree (which implies
442 * that it can only be called by a process thread)
444 virtual bool get_sync_offset (pframes_t& /*offset*/) const { return false; }
446 /** Create a new thread suitable for running part of the buffer process
447 * cycle (i.e. Realtime scheduling, memory allocation, etc. etc are all
448 * correctly setup), with a stack size given in bytes by specified @param
449 * stacksize. The thread will begin executing @param func, and will exit
450 * when that function returns.
452 virtual int create_process_thread (boost::function<void()> func) = 0;
454 /** Wait for all processing threads to exit.
456 * Return zero on success, non-zero on failure.
458 virtual int join_process_threads () = 0;
460 /** Return true if execution context is in a backend thread
462 virtual bool in_process_thread () = 0;
464 /** Return the minimum stack size of audio threads in bytes
466 static size_t thread_stack_size () { return 100000; }
468 /** Return number of processing threads
470 virtual uint32_t process_thread_count () = 0;
472 virtual void update_latencies () = 0;
474 /** Set @param speed and @param position to the current speed and position
475 * indicated by some transport sync signal. Return whether the current
476 * transport state is pending, or finalized.
478 * Derived classes only need implement this if they provide some way to
479 * sync to a transport sync signal (e.g. Sony 9 Pin) that is not
480 * handled by Ardour itself (LTC and MTC are both handled by Ardour).
481 * The canonical example is JACK Transport.
483 virtual bool speed_and_position (double& speed, framepos_t& position) {
492 virtual int _start (bool for_latency_measurement) = 0;
495 struct LIBARDOUR_API AudioBackendInfo {
498 /** Using arg1 and arg2, initialize this audiobackend.
500 * Returns zero on success, non-zero otherwise.
502 int (*instantiate) (const std::string& arg1, const std::string& arg2);
504 /** Release all resources associated with this audiobackend
506 int (*deinstantiate) (void);
508 /** Factory method to create an AudioBackend-derived class.
510 * Returns a valid shared_ptr to the object if successfull,
511 * or a "null" shared_ptr otherwise.
513 boost::shared_ptr<AudioBackend> (*factory) (AudioEngine&);
515 /** Return true if the underlying mechanism/API has been
516 * configured and does not need (re)configuration in order
517 * to be usable. Return false otherwise.
519 * Note that this may return true if (re)configuration, even though
520 * not currently required, is still possible.
522 bool (*already_configured)();
527 #endif /* __libardour_audiobackend_h__ */