1. An Introduction to JACK
A short history and discussion of the JACK Audio Connection Kit, its operating principles, design and implementation
Bob Ham

2. Outline
A short history of JACK
Some sound card basics
The JACK system

3. A short history of JACK ALSA/OSS, LADSPA
Many applications operating only on sound card
Linux-Audio-Developers list, May 2001
Discussion of low-latency, sample-synchronous inter-application data exchange system
Checks indicated usable context-switching
Implemented by Paul Davis

4. IRQ Sound card basics Sound card Sound card read pointer Buffer 1
Computer write pointer

5. IRQ Sound card basics Sound card Computer write pointer Buffer 1
Sound card read pointer

6. Underrun Sound card basics Sound card Computer write pointer Buffer 1
Sound card read pointer

7. The JACK system Audio devices are mmap()d Callback-based
Real-time scheduling
Kernel patches
No read()/write()
No malloc()
No mutexes
Context-switch control through FIFOs

8. A JACK callback int process (jack_nframes_t nframes, void *arg) {
jack_default_audio_sample_t *out =
(jack_default_audio_sample_t *)
jack_port_get_buffer (output_port, nframes);
jack_default_audio_sample_t *in =
jack_port_get_buffer (input_port, nframes);
memcpy (out, in,
sizeof (jack_default_audio_sample_t)
* nframes);
return 0; }

9. JACK driver engine from last client jackd unix sockets to next client
RT thread
libjack
callback
client

10. JACK
driver
engine
jackd
client 1
client 2
client 3

11. and now for some fun...