[alsa-devel] [RFC - AAF PCM plugin 2/5] aaf: Load configuration parameters

[Pierre-Louis Bossart]

On 8/20/18 8:06 PM, Andre Guedes wrote:
> This patch implements the infrastructure to load the plugin
> configuration from ALSA configuration file. The configuration
> is loaded in open() callback.
> 
> All configuration parameters are described in details in doc/aaf.txt
> file.
> 
> Signed-off-by: Andre Guedes <andre.guedes at intel.com>
> ---
>   aaf/pcm_aaf.c | 126 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   doc/aaf.txt   |  52 ++++++++++++++++++++++++
>   2 files changed, 178 insertions(+)
> 
> diff --git a/aaf/pcm_aaf.c b/aaf/pcm_aaf.c
> index 7890e10..4c6f031 100644
> --- a/aaf/pcm_aaf.c
> +++ b/aaf/pcm_aaf.c
> @@ -20,11 +20,133 @@
>   
>   #include <alsa/asoundlib.h>
>   #include <alsa/pcm_external.h>
> +#include <linux/if.h>
> +#include <linux/if_ether.h>
> +#include <string.h>
> +#include <stdint.h>
> +
> +#define NSEC_PER_USEC		1000ULL
>   
>   typedef struct {
>   	snd_pcm_ioplug_t io;
> +
> +	char ifname[IFNAMSIZ];
> +	uint8_t addr[ETH_ALEN];
> +	int prio;
> +	uint64_t streamid;
> +	int mtt;
> +	int t_uncertainty;
> +	int frames_per_pkt;
>   } snd_pcm_aaf_t;
>   
> +static int aaf_load_config(snd_pcm_aaf_t *aaf, snd_config_t *conf)
> +{
> +	snd_config_iterator_t cur, next;
> +
> +	snd_config_for_each(cur, next, conf) {
> +		snd_config_t *entry = snd_config_iterator_entry(cur);
> +		const char *id;
> +
> +		if (snd_config_get_id(entry, &id) < 0)
> +			goto err;
> +
> +		if (strcmp(id, "comment") == 0 ||
> +		    strcmp(id, "type") == 0 ||
> +		    strcmp(id, "hint") == 0)
> +			continue;
> +
> +		if (strcmp(id, "ifname") == 0) {
> +			const char *ifname;
> +
> +			if (snd_config_get_string(entry, &ifname) < 0)
> +				goto err;
> +
> +			snprintf(aaf->ifname, sizeof(aaf->ifname), "%s",
> +				 ifname);
> +		} else if (strcmp(id, "addr") == 0) {
> +			const char *addr;
> +			int n;
> +
> +			if (snd_config_get_string(entry, &addr) < 0)
> +				goto err;
> +
> +			n = sscanf(addr, "%hhx:%hhx:%hhx:%hhx:%hhx:%hhx",
> +				   &aaf->addr[0], &aaf->addr[1],
> +				   &aaf->addr[2], &aaf->addr[3],
> +				   &aaf->addr[4], &aaf->addr[5]);
> +			if (n != 6)
> +				goto err;
> +		} else if (strcmp(id, "prio") == 0) {
> +			long prio;
> +
> +			if (snd_config_get_integer(entry, &prio) < 0)
> +				goto err;
> +
> +			if (prio < 0)
> +				goto err;
> +
> +			aaf->prio = prio;
> +		} else if (strcmp(id, "streamid") == 0) {
> +			const char *streamid;
> +			int n;
> +			uint64_t buf[7];
> +
> +			if (snd_config_get_string(entry, &streamid) < 0)
> +				goto err;
> +
> +			n = sscanf(streamid, "%lx:%lx:%lx:%lx:%lx:%lx:%lx",
> +				   &buf[0], &buf[1], &buf[2], &buf[3],
> +				   &buf[4], &buf[5], &buf[6]);
> +			if (n != 7)
> +				goto err;
> +
> +			aaf->streamid = buf[0] << 56 | buf[1] << 48 |
> +					buf[2] << 40 | buf[3] << 32 |
> +					buf[4] << 24 | buf[5] << 16 |
> +					buf[6];
> +		} else if (strcmp(id, "mtt") == 0) {
> +			long mtt;
> +
> +			if (snd_config_get_integer(entry, &mtt) < 0)
> +				goto err;
> +
> +			if (mtt < 0)
> +				goto err;
> +
> +			aaf->mtt = mtt * NSEC_PER_USEC;
> +		} else if (strcmp(id, "time_uncertainty") == 0) {
> +			long t_uncertainty;
> +
> +			if (snd_config_get_integer(entry, &t_uncertainty) < 0)
> +				goto err;
> +
> +			if (t_uncertainty < 0)
> +				goto err;
> +
> +			aaf->t_uncertainty = t_uncertainty * NSEC_PER_USEC;
> +		} else if (strcmp(id, "frames_per_pkt") == 0) {
> +			long frames_per_pkt;
> +
> +			if (snd_config_get_integer(entry, &frames_per_pkt) < 0)
> +				goto err;
> +
> +			if (frames_per_pkt < 0)
> +				goto err;
> +
> +			aaf->frames_per_pkt = frames_per_pkt;
> +		} else {
> +			SNDERR("Invalid configuration: %s", id);
> +			goto err;
> +		}
> +	}
> +
> +	return 0;
> +
> +err:
> +	SNDERR("Error loading device configuration");
> +	return -EINVAL;
> +}
> +
>   static int aaf_close(snd_pcm_ioplug_t *io)
>   {
>   	snd_pcm_aaf_t *aaf = io->private_data;
> @@ -70,6 +192,10 @@ SND_PCM_PLUGIN_DEFINE_FUNC(aaf)
>   		return -ENOMEM;
>   	}
>   
> +	res = aaf_load_config(aaf, conf);
> +	if (res < 0)
> +		goto err;
> +
>   	aaf->io.version = SND_PCM_IOPLUG_VERSION;
>   	aaf->io.name = "AVTP Audio Format (AAF) Plugin";
>   	aaf->io.callback = &aaf_callback;
> diff --git a/doc/aaf.txt b/doc/aaf.txt
> index 22144de..24ea888 100644
> --- a/doc/aaf.txt
> +++ b/doc/aaf.txt
> @@ -16,3 +16,55 @@ The AAF plugin uses libavtp to handle AVTP packetization. Libavtp source code
>   can be found in https://github.com/AVnu/libavtp as well as instructions to
>   build and install it. If libavtp isn't detected by configure, the plugin isn't
>   built.
> +
> +Plugin Configuration
> +--------------------
> +
> +The plugin parameters are passed via ALSA configuration file. They are defined
> +as follows:
> +
> +	* ifname: Network interface used to transmit/receive AVTP packets.
> +
> +	* addr: Stream destination MAC address.

including multi-cast address?

> +
> +	* prio: Priority used by the plugin to transmit AVTP traffic. This
> +	  option is relevant only when operating in playback mode.
> +
> +	* streamid: Stream ID associated with the AAF stream transmitted or
> +	  received by the plugin.

So the streamid has to be statically configured, right?
If there an assumption that all streams exposed in this configuration 
file can all be used concurrently? Or put differently that the streams 
are only exposed if they can be used independently at any time?

> +
> +	* mtt: Maximum Transit Time (in microseconds) as defined in AVTP spec
> +	  section 4.3.3. This option is relevant only when operating in
> +	  playback mode.
> +
> +	* time_uncertainty: Maximum Time Uncertainty (in microseconds) as
> +	  defined by AVTP spec section 4.3.3. This option is relevant only when
> +	  operating in playback mode.
> +
> +	* frames_per_pkt: Number of audio frames transmitted in one AVTP
> +	  packet.
> +
> +The plugin provides the PCM type "aaf". Configure an AAF PCM virtual device
> +according to the AAF stream you want to transmit or receive. A hypothetical
> +configuration file is shown below:
> +
> +	pcm.aaf {
> +		type aaf
> +		ifname eth0
> +		addr AA:AA:AA:AA:AA:AA
> +		prio 3
> +		streamid BB:BB:BB:BB:BB:BB:0001
> +		mtt 2000
> +		time_uncertainty 125
> +		frames_per_pkt 6
> +	}
> +
> +Put the above to ~/.asoundrc (or /etc/asound.conf), and use the AAF PCM virtual
> +device with your ALSA apps. For example, to stream the content from a wav file
> +through the network, run:
> +
> +	$ aplay -Daaf foo.wav

How do you deal with multiple streams then? -Daaf:<stream_number> ?

> +
> +To receive the AAF stream generated by the previous command, run:
> +
> +	$ arecord -Daaf

Did you mean on a different machine or are there any loopback capabilities?