Re: [linux-audio-dev] audioengine/laaga prototype now operational (audible)

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Subject: Re: [linux-audio-dev] audioengine/laaga prototype now operational (audible)
From: Richard Guenther (rguenth_AT_tat.physik.uni-tuebingen.de)
Date: Mon Jun 18 2001 - 12:24:06 EEST

On Sun, 17 Jun 2001, Paul Davis wrote:

> Your comments on the emerging design would be very welcome.

Instead of opposing against the whole design, I'll just start
commenting on the actual interface (audioengine.h):

audioengine_handle_t *
audioengine_open (const char *client_name,
                  AudioengineProcessCallback, void *process_arg,
                  AudioengineBufferSizeCallback, void *bufsize_arg,
                  AudioengineSampleRateCallback, void *srate_arg);

I dont like having more than one callback at all. Instead the client
should query the buffer size (whats that at all!?? maximum buffersize?
Not again something like LADSPA delay_10ms delay_500ms delay_1s sort
of crap...). Also the sample rate should be per connection and
constant during its lifetime (just transparently disconnect/reconnect
from the UI, if you like) - we want to support resampling nodes,
dont we?

Also, is this "client_name" a port? Why do I register the process
callback wrt the registration of my app to the engine? Isnt that
process a per-port-bundle operation? I.e. more like

audioengine_open(const char *client_name);

port_bundle_t *
audioengine_new_port_bundle(const char *name, (* process)());
audioengine_register_port(const char *port_name, port_bundle_t *);

(so you'd usually group things like left/right but not necessarily
two instances of that)

Or you planned to support multiple audioengine_open() calls per
process? 

---

int audioengine_activate (audioengine_handle_t *handle);
int audioengine_deactivate (audioengine_handle_t *handle);

I dont see you need those for an always-running-system. Perhaps
be able to "mute"/"suspend" a connection, but not the app

----

audioengine_port_t *
audioengine_port_register (audioengine_handle_t *,
                           const char *port_name,
                           const char *port_type,
                           unsigned long flags,
                           unsigned long buffer_size);

whats a physical connection!??? whats a multi connection!????
Either those are always possible (engine driven) or explicit - you
dont need those flags.
Drop buffer_size, too. In fact - drop support for different typed
data than audio - you have too much specific stuff in the engine
based approach anyway. ==>> make it simple.

----

int audioengine_port_unregister (audioengine_handle_t *,
audioengine_port_t *);

You dont need the engine handle.

----

int audioengine_port_lock (audioengine_handle_t *, const char *port_name);
int audioengine_port_unlock (audioengine_handle_t *, const char
*port_name);

You dont need those - instead make the ports reference counted by the
number of open connections and gc them, if they were deleted and no
connections are there.

----

unsigned long audioengine_get_sample_rate (audioengine_handle_t *);
unsigned long audioengine_get_buffer_size (audioengine_handle_t *);

Make this per port/connection. Dont allow them to change during
port (yes!) or connection (at least that) lifetime.

----

GSList *audioengine_get_ports (audioengine_handle_t *,
                               const char *port_name_pattern,
                               const char *type_name_pattern,
                               unsigned long flags);

Dont use GSList's :) List of returned ports are the port identifier
strings (the spec doesnt tell).

----

void audioengine_listen_for_ports (audioengine_handle_t *,
AudioenginePortRegistrationCallback, void *);

Uh - if you want to allow highlevel events from the engine, just
use some more abstract stuff like a SYSV message queue for that
(not another callback...), then you can add messages without adding
more calls.

----

char *audioengine_port_name (audioengine_port_t *port, char *buf, unsigned
int bufsize);

you cant get hold of the audioengine_port_t if you;re not the one who
registered it? So I think this call is pointless. Also do not design
such "compound" I-support-every-kind-of-arg-you-can-think-of calls :)
Just use

char *audioengine_port_name (audioengine_port_t *port);

its not performace critical at all.

----

audioengine_port_t *audioengine_port_by_id (audioengine_handle_t *handle,
audioengine_port_id_t);

Ah - here it is. Whats the port_id ?? You have a unique string identifier,
so how you need another id?
HINT: for internal (inter-process) use just use the virtual address
      (for shm the offset inside the segment) of the struct. Quite a
      useful unique identifier.

Richard.

--
Richard Guenther <richard.guenther_AT_uni-tuebingen.de>
WWW: http://www.tat.physik.uni-tuebingen.de/~rguenth/
The GLAME Project: http://www.glame.de/

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