Mike Brady
60143518c2
- 48,000 frames per second operation, - 48k lossless stereo, 5.1 and 7.1 surround sound - Multichannel and multi rate operation on ALSA, PipeWire, PulseAudio, FreeBSD, stdout and unix pipe output backends. Automatic, flexible and controllable output format (rate, sample format and channel count) selection. Full FFmpeg integration to support transcoding, resampling, and new audio formats. Better operation on lower powered devices down to e.g. Raspberry Pi B. Reduced Docker image sizes with a slimmed-down FFmpeg library. Enhanced timestamp handling for better synchronization. Improved the sync error calculation. A new "vernier" resampling and interpolation method for low-power CPUs. Bug fixes and minor enhancements. Note -- there are many breaking changes from previous versions of Shairport Sync!
79 lines
3.5 KiB
C
79 lines
3.5 KiB
C
/*
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* This file is part of the nqptp distribution (https://github.com/mikebrady/nqptp).
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* Copyright (c) 2021--2025 Mike Brady.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, version 2.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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* Commercial licensing is also available.
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*/
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#ifndef NQPTP_SHM_STRUCTURES_H
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#define NQPTP_SHM_STRUCTURES_H
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#define NQPTP_INTERFACE_NAME "/nqptp"
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#define NQPTP_SHM_STRUCTURES_VERSION 10
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#define NQPTP_CONTROL_PORT 9000
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// The control port expects a UDP packet with the first character being a command letter
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// and the rest being any arguments, the whole not to exceed 4096 characters.
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// The "T" command, must followed by nothing or by
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// a space and a space-delimited list of IPv4 or IPv6 numbers.
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// The IPs, if provided, will become the new list of timing peers, replacing any
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// previous list. The first IP number is the clock that NQPTP will listen to.
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// The remaining IP address are the addresses of all the timing peers. The timing peers
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// are not used in this version of NQPTP.
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// If no timing list is provided, the existing timing list is deleted.
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// The "B" command is a message that the client -- which generates the clock --
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// is about to start playing.
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// NQPTP uses it to determine that the clock is active and will not sleep.
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// The "E" command signifies that the client has stopped playing and that
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// the clock may shortly sleep.
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// The "P" command signifies that SPS has paused play (buffered audio only).
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// The clock seems to stay running in this state.
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// When the clock is active, it is assumed that any decreases in the offset
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// between the local and remote clocks are due to delays in the network.
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// NQPTP smooths the offset by clamping any decreases to a small value.
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// In this way, it can follow clock drift but ignore network delays.
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// When the clock is inactive, it can stop running. This causes the offset to decrease.
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// NQPTP clock smoothing would treat this as a network delay, causing true sync to be lost.
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// To avoid this, when the clock goes from inactive to active,
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// NQPTP resets clock smoothing to the new offset.
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#include <inttypes.h>
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#include <pthread.h>
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typedef struct {
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uint64_t master_clock_id; // the current master clock
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uint64_t local_time; // the time when the offset was calculated
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uint64_t local_to_master_time_offset; // add this to the local time to get master clock time
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uint64_t master_clock_start_time; // this is when the master clock became master
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} shm_structure_set;
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// The actual interface comprises a shared memory region of type struct shm_structure.
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// This comprises two records of type shm_structure_set.
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// The secondary record is written strictly after all writes to the main record are
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// complete. This is ensured using the __sync_synchronize() construct.
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// The reader should ensure that both copies match for a read to be valid.
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// For safety, the secondary record should be read strictly after the first.
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struct shm_structure {
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uint16_t version; // check this is equal to NQPTP_SHM_STRUCTURES_VERSION
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shm_structure_set main;
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shm_structure_set secondary;
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};
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#endif
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