Jack Port and Integration on MacOSX Stphane Letz Grame, centre de - - PowerPoint PPT Presentation

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Jack Port and Integration on MacOSX

Stéphane Letz Grame, centre de création musicale Lyon, France

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Plan

• Porting the Linux code to MacOSX
• Integration with CoreAudio architecture : the JackOSX project
• Jackd evolution : more structure, multi-processor version

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Porting the Linux code

• Use of the POSIX shared memory API more reliable on MacOSX
• Rewriting the engine audio cycle for a callback-based activation scheme
• Using Mach Remote Procedure Call for client activation : the Linux FIFO based code is not used

anymore, all clients are activated in a loop inside the Jack engine

• - Synchronous RPC are fast because the scheduler is bypassed
• - Thread migration : the calling thread parameters (priority, time quantum..) are transferred to the called thread
• Client Real-Time threads : fixed priority time constrained threads (period, computation, constraint)
• Use an additional real-time thread for client process call

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

• Current one : a PortAudio based driver that can also work on Linux
• In development : a more efficient “native” CoreAudio based driver, using the Apple HALOuputUnit

component (takes care of all audio stream adaptation)

Drivers

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Performance

• Measuring the audio cycle on a iBook G3/700 using jackd timing code
• At 64 frames : finding the maximum additional latency
• jackd only : ~ 5 us (0.5 %)
• jackd + 1 jack_metro client : ~ 55 us (3.5 %)
• jackd + 1 jack_metro client + moving windows + network access… : up to ~ 260 us
• jackd + 2 jack_metro clients : ~ 120 us (7.5 %)
• jackd + 2 jack_metro clients + moving windows + network access… : up to ~ 360 us
• Maximum additional latency of about 200 us
• Really stable
• Jackd can be used with 32 frame buffers
• At 64 frames : client activation time : ~ 50 us (jack_metro in “thru” mode)

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Integration in the CoreAudio architecture

MacOSX audio architecture : HAL : Hardware Abstraction Layer in user space : multi-channel audio, real-time thread activation (for Audio callback), mixing for output…, expose the API for applications IOKIT : a C++ based layer that implements generic services for driver developers Drivers : kernel drivers, interaction with the hardware

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

HAL model

• A “software interrupt” based model
• Each client can use its own buffer size (starting from 14 frames…)
• The HAL takes care of waking-up real-time (callback) threads at the right time
• All real-time threads run at a fixed priority, but correct thread interleaving is done by the HAL by carefully

setting the time-constraint parameters : period, computation, constraint

• Drivers usually publish their “native” capabilities : stream and sample format, sample rate, buffer size….
• Application may use optimized (Altivec…) AudioConverter components to convert in their own format if

needed

• AudioUnits : a plug-in API to be used by host applications

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Jack Audio Router (JAR)

The bridge between regular CoreAudio applications and the Jack server

• Using JAR, a CoreAudio application becomes a Jack client
• A user space driver placed between the HAL and IOKit layer
• Implements the HAL “Plug-in API”
• Loaded by the HAL like kernel drivers to become available for applications

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

JAR (2) : behaviour

• JAR presents itself as an n mono non-interleaved stream, fixed buffer size, fixed sample rate

driver

• Behaves like a kernel driver for the HAL, will be available like other drivers for applications
• Can be used as the default system driver for applications like iTunes, QuickTime Player, DLSSynth…

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

JAR (3) : mapping the CoreAudio API on the Jack API

• Parameter query API : AudioDeviceGetProperty
• Client activation

AudioDeviceAddIOProc ==> jack_client_new jack_client_port_register jack_set_process_callback AudioDeviceStopOProc ==> jack_client_deactivate AudioDeviceStartIOProc ==> jack_client_activate AudioDeviceRemoveIOProc ==> jack_client_port_unregister jack_client_close

• Described in global settings :
• number of input/ouput jack ports
• auto connection with drivers
• JAR as default system driver

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Jack Plug-ins, JackPilot

• Extend the audio routing capabilities inside plug-ins host applications : track insert…..
• JackAU (AudioUnit API) and JackVST (VST API)
• JackPilot : global settings : jackd parameters, connections manager

CoreAudio Applications (with plugin support) Cubase SX, Logic, Max/MSP ... JackVST or JackAU channel insert … CoreAudio Applications (with plugin support) Cubase SX, Logic, Max/MSP ... JackVST or JackAU channel insert … Audio Hardware Built-In, MOTU 828 … CoreAudio Applications (without plugin support) Reason, iTunes, Quicktime ...

Native Jack Clients

Pure Data

Jack Server

JAR JAR

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

JackOSX project

• All the components are distributed in a package called JackOSX
• Source Forge project : JAR, Jack Plug-ins, CoreAudio drivers
• Web site : www.jackosx.com
• In collaboration with Johnny Petrantoni and Dan Nigrin

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Synchronization

• Allowing transparent synchronization between Jack native clients and CoreAudio applications
• Mapping the Jack transport API to the MIDI clock sync API
• Converting Jack transport state events to MIDI Start, Stop, Continue, SongPos messages

using the CoreMIDI API

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Jack evolution : MacOSX specifics

• In MacOSX, the natural way to implement a server/client system is to use the

Mach Interface Generator (MIG) to define new Remote Procedure Calls

• Synchronous and asynchronous functions can be defined :
• function call is actually done using Mach ports and messages
• MIG takes care of parameter management
• synchronous calls are implemented with send/receive Mach messages

that use the fast “thread migration” system

• Socket based communications can be completely suppressed
• The server defines a public Mach port for client/server communication
• When opening, each client defines its own private port for server/client communication
• Opening a client : rpc_jack_client_new (mach_port_t server, const char* name, int* refnum…)
• Calling the client process callback : rpc_jack_client_process(mach_port_t client, jack_frame_t frames,….)

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Multi-processor version (1)

• In the current version, the client graph is sorted to determine an order for client activation

each time the graph topology changes

• Multi-processor version : activate parallel nodes on different processors
• no more “a priori” sorting
• a data flow model : a node become runnable when all of its input ports

have been filled up

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Multi-processor version (2)

• Using system primitives :
• describe data dependencies between nodes with semaphores
• need of inter-process semaphores
• Implementing a “mini” scheduler, for an audio cycle :
• starting from the input, find all runnable nodes, put them on a lock-free shared list
• one thread per processor that takes a runnable node, execute it, propagate output port “readiness”

to connected inputs

• re-compute runnable nodes
• until all nodes have been executed

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Jackd architecture re-organisation (1)

• More structure:
• Isolate the server/client communication code
• Isolate the client activation code (FIFO on Linux, futexes on kernel 2.6, synchronous

RPC on MacOSX, semaphores…)

• More secure use of shared memory segment : distinguish between R/W and R only

segments on the client side

• Move all port data structure and connections to shared memory
• Thinking in term of lock-free access whenever possible

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

Jackd architecture re-organisation (2)

• More structure :
• Moving the FreeWheel code as an autonomous driver
• Isolate Watch Dog thread code

……

• Fix some API problems :
• Memory leak (jack_port_by_id and jack_port_by_name…)
• Some state change are not notified to other clients : change of port names…

……

GRAME : Centre National de Création Musicale LAD 2004 : Jack Port and Integration on MacOSX

DEMO