FreeBSD: Add synced OSS operation (sosso) headers.

As a header-only C++ library, synced OSS operation (sosso) is used to
clean up and separate the low-level handling of FreeBSD OSS devices
in JACK. Features include:

 * Supports both read() / write() and mmap() IO operation.
 * Adaptive polling, better suited for low-latency requirements.
 * Internal double buffer to avoid troubles with OSS buffer resize.
 * Closely monitors progress and drift for each channel (+/- 1ms).
 * Facilitates drift correction through buffer offsets.
 * Depends on C++ standard library and system headers, nothing else.

Although the sosso library is somewhat tailored to the needs of JACK,
it was developed separately and will eventually be published and / or
used in other projects. Therefore the headers follow a different
formatting style and are more liberally licensed (ISC).

freebsd/sosso/Buffer.hpp

@@ -0,0 +1,153 @@
+/*
+ * Copyright (c) 2023 Florian Walpen <[email protected]>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef SOSSO_BUFFER_HPP
+#define SOSSO_BUFFER_HPP
+
+#include <cstring>
+
+namespace sosso {
+
+/*!
+ * \brief Buffer Management
+ *
+ * Provides means to access and manipulate externally allocated buffer memory.
+ * It stores a memory pointer, length and a read / write position. The buffer
+ * memory can be passed from one Buffer instance to another, through move
+ * constructor and move assignment. This prevents multiple Buffer instances from
+ * referencing the same memory.
+ */
+class Buffer {
+public:
+  //! Construct an empty and invalid Buffer.
+  Buffer() = default;
+
+  /*!
+   * \brief Construct Buffer operating on given memory.
+   * \param buffer Pointer to the externally allocated memory.
+   * \param length Length of the memory dedicated to this Buffer.
+   */
+  Buffer(char *buffer, std::size_t length)
+      : _data(buffer), _length(length), _position(0) {}
+
+  /*!
+   * \brief Move construct a buffer.
+   * \param other Adopt memory from this Buffer, leaving it empty.
+   */
+  Buffer(Buffer &&other) noexcept
+      : _data(other._data), _length(other._length), _position(other._position) {
+    other._data = nullptr;
+    other._position = 0;
+    other._length = 0;
+  }
+
+  /*!
+   * \brief Move assign memory from another Buffer.
+   * \param other Adopt memory from this Buffer, leaving it empty.
+   * \return This newly assigned Buffer.
+   */
+  Buffer &operator=(Buffer &&other) {
+    _data = other._data;
+    _position = other._position;
+    _length = other._length;
+    other._data = nullptr;
+    other._position = 0;
+    other._length = 0;
+    return *this;
+  }
+
+  //! Buffer is valid if the memory is accessable.
+  bool valid() const { return (_data != nullptr) && (_length > 0); }
+
+  //! Access the underlying memory, null if invalid.
+  char *data() const { return _data; }
+
+  //! Length of the underlying memory in bytes, 0 if invalid.
+  std::size_t length() const { return _length; }
+
+  //! Access buffer memory at read / write position.
+  char *position() const { return _data + _position; }
+
+  //! Get read / write progress from buffer start, in bytes.
+  std::size_t progress() const { return _position; }
+
+  //! Remaining buffer memory in bytes.
+  std::size_t remaining() const { return _length - _position; }
+
+  /*!
+   * \brief Cap given progress by remaining buffer memory.
+   * \param progress Progress in bytes.
+   * \return Progress limited by the remaining buffer memory.
+   */
+  std::size_t remaining(std::size_t progress) const {
+    if (progress > remaining()) {
+      progress = remaining();
+    }
+    return progress;
+  }
+
+  //! Indicate that the buffer is fully processed.
+  bool done() const { return _position == _length; }
+
+  //! Advance the buffer read / write position.
+  std::size_t advance(std::size_t progress) {
+    progress = remaining(progress);
+    _position += progress;
+    return progress;
+  }
+
+  //! Rewind the buffer read / write position.
+  std::size_t rewind(std::size_t progress) {
+    if (progress > _position) {
+      progress = _position;
+    }
+    _position -= progress;
+    return progress;
+  }
+
+  /*!
+   * \brief Erase an already processed part, rewind.
+   * \param begin Start position of the region to be erased.
+   * \param end End position of the region to be erased.
+   * \return The number of bytes that were effectively erased.
+   */
+  std::size_t erase(std::size_t begin, std::size_t end) {
+    if (begin < _position && begin < end) {
+      if (end > _position) {
+        end = _position;
+      }
+      std::size_t copy = _position - end;
+      if (copy > 0) {
+        std::memmove(_data + begin, _data + end, copy);
+      }
+      _position -= (end - begin);
+      return (end - begin);
+    }
+    return 0;
+  }
+
+  //! Reset the buffer position to zero.
+  void reset() { _position = 0; }
+
+private:
+  char *_data = nullptr;     // External buffer memory, null if invalid.
+  std::size_t _length = 0;   // Total length of the buffer memory.
+  std::size_t _position = 0; // Current read / write position.
+};
+
+} // namespace sosso
+
+#endif // SOSSO_BUFFER_HPP

freebsd/sosso/Channel.hpp

@@ -0,0 +1,210 @@
+/*
+ * Copyright (c) 2023 Florian Walpen <[email protected]>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef SOSSO_CHANNEL_HPP
+#define SOSSO_CHANNEL_HPP
+
+#include "sosso/Device.hpp"
+#include <algorithm>
+
+namespace sosso {
+
+/*!
+ * \brief Audio Channel of a Device
+ *
+ * As a base class for read and write channels, this class provides generic
+ * handling of progress, loss and wakeup times. Progress here means the OSS
+ * device captures or consumes audio data, in frames. When progress is detected
+ * within a short wakeup interval, this counts as a sync where we can exactly
+ * match the device progress to current time.
+ * The balance indicates the drift between device progress and external time,
+ * usually taken from FrameClock.
+ * At device start and after loss, device progress can be irregular and is
+ * temporarily decoupled from Channel progress (freewheel). Sync events are
+ * required to change into normal mode which strictly follows device progress.
+ */
+class Channel : public Device {
+public:
+  /*!
+   * \brief Open the device, initialize Channel
+   * \param device Full device path.
+   * \param mode Open mode (read / write).
+   * \return True if successful.
+   */
+  bool open(const char *device, int mode) {
+    // Reset all internal statistics from last run.
+    _last_processing = 0;
+    _last_sync = 0;
+    _last_progress = 0;
+    _balance = 0;
+    _min_progress = 0;
+    _max_progress = 0;
+    _total_loss = 0;
+    _sync_level = 8;
+    return Device::open(device, mode);
+  }
+
+  //! Total progress of the device since start.
+  std::int64_t last_progress() const { return _last_progress; }
+
+  //! Balance (drift) compared to external time.
+  std::int64_t balance() const { return _balance; }
+
+  //! Last time there was a successful sync.
+  std::int64_t last_sync() const { return _last_sync; }
+
+  //! Last time the Channel was processed (mark_progress()).
+  std::int64_t last_processing() const { return _last_processing; }
+
+  //! Maximum progress step encountered.
+  std::int64_t max_progress() const { return _max_progress; }
+
+  //! Minimum progress step encountered.
+  std::int64_t min_progress() const { return _min_progress; }
+
+  //! Current number of syncs required to change to normal mode.
+  unsigned sync_level() const { return _sync_level; }
+
+  //! Indicate Channel progress decoupled from device progress.
+  bool freewheel() const { return _sync_level > 4; }
+
+  //! Indicate a full resync with small wakeup steps is required.
+  bool full_resync() const { return _sync_level > 2; }
+
+  //! Indicate a resync is required.
+  bool resync() const { return _sync_level > 0; }
+
+  //! Total number of frames lost due to over- or underruns.
+  std::int64_t total_loss() const { return _total_loss; }
+
+  //! Next time a device progress could be expected.
+  std::int64_t next_min_progress() const {
+    return _last_progress + _min_progress + _balance;
+  }
+
+  //! Calculate safe wakeup time to avoid over- or underruns.
+  std::int64_t safe_wakeup(std::int64_t oss_available) const {
+    return next_min_progress() + buffer_frames() - oss_available -
+           max_progress();
+  }
+
+  //! Estimate the time to expect over- or underruns.
+  std::int64_t estimated_dropout(std::int64_t oss_available) const {
+    return _last_progress + _balance + buffer_frames() - oss_available;
+  }
+
+  /*!
+   * \brief Calculate next wakeup time.
+   * \param sync_target External wakeup target like the next buffer end.
+   * \param oss_available Number of frames available in OSS buffer.
+   * \return Next wakeup time in external frame time.
+   */
+  std::int64_t wakeup_time(std::int64_t sync_target,
+                           std::int64_t oss_available) const {
+    // Use one sync step by default.
+    std::int64_t wakeup = _last_processing + Device::stepping();
+    if (freewheel() || full_resync()) {
+      // Small steps when doing a full resync.
+    } else if (resync() || wakeup + max_progress() > sync_target) {
+      // Sync required, wake up prior to next progress if possible.
+      if (next_min_progress() > wakeup) {
+        wakeup = next_min_progress() - Device::stepping();
+      } else if (next_min_progress() > _last_processing) {
+        wakeup = next_min_progress();
+      }
+    } else {
+      // Sleep until prior to sync target, then sync again.
+      wakeup = sync_target - max_progress();
+    }
+    // Make sure we wake up at sync target.
+    if (sync_target > _last_processing && sync_target < wakeup) {
+      wakeup = sync_target;
+    }
+    // Make sure we don't sleep into an OSS under- or overrun.
+    if (safe_wakeup(oss_available) < wakeup) {
+      wakeup = std::max(safe_wakeup(oss_available),
+                        _last_processing + Device::stepping());
+    }
+    return wakeup;
+  }
+
+protected:
+  // Account for progress detected, at current time.
+  void mark_progress(std::int64_t progress, std::int64_t now) {
+    if (progress > 0) {
+      if (freewheel()) {
+        // Some cards show irregular progress at the beginning, correct that.
+        // Also correct loss after under- and overruns, assume same balance.
+        _last_progress = now - progress - _balance;
+        // Require a sync before transition back to normal processing.
+        if (now <= _last_processing + stepping()) {
+          _sync_level -= 1;
+        }
+      } else if (now <= _last_processing + stepping()) {
+        // Successful sync on progress within small processing steps.
+        _balance = now - (_last_progress + progress);
+        _last_sync = now;
+        if (_sync_level > 0) {
+          _sync_level -= 1;
+        }
+        if (progress < _min_progress || _min_progress == 0) {
+          _min_progress = progress;
+        }
+        if (progress > _max_progress) {
+          _max_progress = progress;
+        }
+      } else {
+        // Big step with progress but no sync, requires a resync.
+        _sync_level += 1;
+      }
+      _last_progress += progress;
+    }
+    _last_processing = now;
+  }
+
+  // Account for loss given progress and current time.
+  std::int64_t mark_loss(std::int64_t progress, std::int64_t now) {
+    // Estimate frames lost due to over- or underrun.
+    std::int64_t loss = (now - _balance) - (_last_progress + progress);
+    return mark_loss(loss);
+  }
+
+  // Account for loss.
+  std::int64_t mark_loss(std::int64_t loss) {
+    if (loss > 0) {
+      _total_loss += loss;
+      // Resync OSS progress to frame time (now) to recover from loss.
+      _sync_level = std::max(_sync_level, 6U);
+    } else {
+      loss = 0;
+    }
+    return loss;
+  }
+
+private:
+  std::int64_t _last_processing = 0; // Last processing time.
+  std::int64_t _last_sync = 0;       // Last sync time.
+  std::int64_t _last_progress = 0;   // Total device progress.
+  std::int64_t _balance = 0;         // Channel drift.
+  std::int64_t _min_progress = 0;    // Minimum progress step encountered.
+  std::int64_t _max_progress = 0;    // Maximum progress step encountered.
+  std::int64_t _total_loss = 0;      // Total loss due to over- or underruns.
+  unsigned _sync_level = 0;          // Syncs required.
+};
+
+} // namespace sosso
+
+#endif // SOSSO_CHANNEL_HPP