Overview

The configuration of streams (talkers and listeners) is controlled via the structure openavb_tl_cfg_t that is passed to the openavbTLConfigure function. There are 3 major sections within the configuration structure. The general talker / listener (AVTP stream) section, the mapping module section and the interface module section. The general section has settings used by the talker/listener module directly. The mapping module section has settings specific to the mapping module being used for the stream and the interface module section has settings specific to the interface module being used for the stream.

How the openavb_tl_cfg_t structure gets set is platform dependent. For the Linux reference implementation reading from .ini files is supported which in turn fills this structure. For RTOSes the stream configuration structure is usually set directly via code in the AVB host application module. Therefore the use of .ini files is a layer above the what the core AVB stack uses. The Release Notes for the AVB port should be referenced with regards to where the configuration values can be set.

Here is a sample configuration structure initialization for a H.264 listener.

void h264_SampleListenerCfg(openavb_tl_cfg_t *cfg)
{
    // Clear our the configuration structure to ensure defaults (0)
    memset(cfg, 0, sizeof(openavb_tl_cfg_t));
    // This must be set to the multicast address that is used 
    U8 multicastStrmAddr[] = { 0x91, 0xE0, 0xF0, 0x00, 0xFE, 0x00 };
    // TL (Talker / Listener) Configuration
    // Identify the role of the stream (talker or listener)
    // must be set to AVB_ROLE_LISTENER or AVB_ROLE_TALKER
    cfg->role = AVB_ROLE_LISTENER;
    memcpy(cfg->stream_addr.buffer.ether_addr_octet, multicastStrmAddr, ETH_ALEN);
    cfg->stream_addr.mac = &cfg->stream_addr.buffer;
    // max_interval_frames: The maximum number of packets that will be sent during 
    // an observation interval. This is only used on the talker.
    // cfg->max_interval_frames = 1;
    // max_transit_usec: Allows manually specifying a maximum transit time. 
    // On the talker this value is added to the PTP walltime to create the AVTP Timestamp.
    // On the listener this value is used to validate an expected valid timestamp range.
    // Note: For the listener the map_nv_item_count value must be set large enough to 
    // allow buffering at least as many AVTP packets that can be transmitted  during this 
    // max transit time.
    cfg->max_transit_usec = 2000;
    // max_transmit_deficit_usec: Allows setting the maximum packet transmit rate deficit that will
    // be recovered when a talker falls behind. This is only used on a talker side. When a talker
    // can not keep up with the specified transmit rate it builds up a deficit and will attempt to 
    // make up for this deficit by sending more packets. There is normally some variability in the 
    // transmit rate because of other demands on the system so this is expected. However, without this
    // bounding value the deficit could grew too large in cases such where more streams are started 
    // than the system can support and when the number of streams is reduced the remaining streams 
    // will attempt to recover this deficit by sending packets at a higher rate. This can cause a problem
    // at the listener side and significantly delay the recovery time before media playback will return 
    // to normal. Typically this value can be set to the expected buffer size (in usec) that listeners are 
    // expected to be buffering. For low latency solutions this is normally a small value. For non-live 
    // media playback such as video playback the listener side buffers can often be large enough to held many
    // seconds of data.
    // cfg->max_transmit_deficit_usec = 2000;
    // internal_latency: Allows mannually specifying an internal latency time. This is used
    // only on the talker.
    //  cfg->internal_latency = 0;
    // The number of microseconds a media queue items can be passed the presentation time at which
    // point it will be purged.
    cfg->max_stale = 500;
    // number of intervals to handle at once (talker)
    // cfg->batch_factor = 1;
    // report_seconds: How often to output stats. Defaults to 10 seconds. 0 turns off the stats. 
    cfg->report_seconds = 0;
    // sr_class: A talker only setting. Values are either SR_CLASS_A or SR_CLASS_B.
    // cfg->sr_class = SR_CLASS_A;
    // raw_tx_buffers: The number of raw socket transmit buffers.
    // cfg->raw_tx_buffers = 40;
    // raw_rx_buffers: The number of raw socket receive buffers.
    cfg->raw_rx_buffers = 40;
    // tx_blocking_in_intf : A talker only option. When set packet pacing is expected to be handled in the interface module.
    // Commonly there will be a matching interface module configuration item that needs to be set.
    // cfg->tx_blocking_in_intf = FALSE;
    // The remaining configuration items vary depending on the mapping module and interface module being used.
    // These configuration values are populated as name value pairs.
    // Configuration index counter.
    int cfgIdx = 0;
    // Mapping module
    // map_nv_item_count: The number of media queue elements to hold.
    cfg->libCfgNames[cfgIdx] = "map_nv_item_count";
    cfg->libCfgValues[cfgIdx++] = "10";
    // map_nv_tx_rate: Transmit rate. Typically this is set to match the SR Class. 8000 for A and 4000 for B
    // cfg->libCfgNames[cfgIdx] = "map_nv_tx_rate";
    // cfg->libCfgValues[cfgIdx++] = "8000";
    // map_nv_max_payload_size: This is the max RTP payload size. See RFC 6184 for details, 
       // 1412 is the default size
    cfg->libCfgNames[cfgIdx] = "map_nv_max_payload_size";
    cfg->libCfgValues[cfgIdx++] = "1412";
    // Interface module
    // intf_nv_blocking_tx_callback : A talker only option. When set packet pacing is expected to be handled in the interface module.
    // Commonly the TL configuration option tx_blocking_in_intf needs to be set to match this.
    // cfg->libCfgNames[cfgIdx] = "intf_nv_blocking_tx_callback";
    // cfg->libCfgValues[cfgIdx++] = "1";
    // intf_nv_ignore_timestamp : If set the listener will ignore the timestamp on media queue items.
    cfg->libCfgNames[cfgIdx] = "intf_nv_ignore_timestamp";
    cfg->libCfgValues[cfgIdx++] = "0";
    cfg->nLibCfgItems = cfgIdx;
    // Mapping and interface modules main initialization entry points
    // pMapInitFn : Mapping module initialization function. (openavb_map_initialize_fn_t)
    cfg->osalCfg.pMapInitFn = openavbMapH264Initialize;
    // pIntfInitFn : Interface module initialization function. (openavb_intf_initialize_fn_t)
    cfg->osalCfg.pIntfInitFn = openavbIntfJ6Video;
} 

Common Stream Configuration

These are common stream configuration values.

Name	Description
role	Sets the process as a talker or listener. Valid values are talker or listener.
stream_addr	Used on the listener and should be set to the mac address of the talker.
stream_uid	The unique stream ID. The talker and listener must both have this set the same.
dest_addr	Destination multicast address for the stream. If using with MAAP - dynamic destination addresses are generated automatically by the talker and passed to the listener, and don't need to be configured. without MAAP, locally administered (static) addresses must be configured. Those addresses are in the range of: 91:E0:F0:00:FE:00 - 91:E0:F0:00:FE:FF. Typically use :00 for the first stream, :01 for the second, etc. If SRP is being used the static destination address only needs to be set in the talker; is not being used the destination address need to be set (to the same value) in both the talker and listener. The destination is a multicast address, not a real MAC address, so it does not match the talker or listener's interface MAC. There are several pools of those addresses for use by AVTP defined in 1722.
max_interval_frames	The maximum number of packets that will be sent during an observation interval. This is only used on the talker.
max_frame_size	Maximum size of the frame
sr_class	A talker only setting. Values are either A or B. If not set an internal default is used.
sr_rank	A talker only setting. If not set an internal default is used.
max_transit_usec	Allows manually specifying a maximum transit time. On the talker this value is added to the PTP walltime to create the AVTP Timestamp. On the listener this value is used to validate an expected valid timestamp range. Note: For the listener the map_nv_item_count value must be set large enough to allow buffering at least as many AVTP packets that can be transmitted during this max transit time.
max_transmit_deficit_usec	Allows setting the maximum packet transmit rate deficit that will be recovered when a talker falls behind. When a talker can not keep up with the specified transmit rate it builds up a deficit and will attempt to make up for this deficit by sending more packets. There is normally some variability in the transmit rate because of other demands on the system so this is expected. However, without this bounding value the deficit could grew too large in cases such where more streams are started than the system can support and when the number of streams is reduced the remaining streams will attempt to recover this deficit by sending packets at a higher rate. This can cause a problem at the listener side and significantly delay the recovery time before media playback will return to normal. Typically this value can be set to the expected buffer size (in usec) that listeners are expected to be buffering. For low latency solutions this is normally a small value. For non-live media playback such as video playback the listener side buffers can often be large enough to held many seconds of data. Note: This is only used on a talker side.
internal_latency	Allows mannually specifying an internal latency time. This is used only on the talker.
max_stale	The number of microseconds beyond the presentation time that media queue items will be purged because they are too old (past the presentation time). This is only used on listener end stations. Note: needing to purge old media queue items is often a sign of some other problem. For example: a delay at stream startup before incoming packets are ready to be processed by the media sink. If this deficit in processing or purging the old (stale) packets is not handled, syncing multiple listeners will be problematic.
raw_tx_buffers	The number of raw socket transmit buffers. Typically 4 - 8 are good values. This is only used by the talker. If not set internal defaults are used.
raw_rx_buffers	The number of raw socket receive buffers. Typically 50 - 100 are good values. This is only used by the listener. If not set internal defaults are used.
report_seconds	How often to output stats. Defaults to 10 seconds. 0 turns off the stats.
tx_blocking_in_intf	The interface module will block until data is available. This is a talker only configuration value and not all interface modules support it.
pMapInitFn	Pointer to the mapping module initialization function. Since this is a pointer to a function addresss is it not directly set in platforms that use a .ini file.
IntfInitFn	Pointer to the interface module initialization function. Since this is a pointer to a function addresss is it not directly set in platforms that use a .ini file.

Platform Specific Stream Configuration Values

Some platform ports have unique configuration values.

Linux

Name	Description
map_lib	The name of the library file (commonly a .so file) that implements the Initialize function. Comment out the map_lib name and link in the .c file to the openavb_tl executable to embed the mapper directly into the executable unit. There is no need to change anything else. The Initialize function will still be dynamically linked in.
map_fn	The name of the initialize function in the mapper
intf_lib	The name of the library file (commonly a .so file) that implements the Initialize function. Comment out the intf_lib name and link in the .c file to the openavb_tl executable to embed the interface directly into the executable unit. There is no need to change anything else. The Initialize function will still be dynamically linked in
intf_fn	The name of the initialize function in the interface

Example Interface / Mapping Combinations

Below are a few interface / mapping module combinations. Notice that a single interface module may work with mutliple mapping modules. Additionally some mappings may work with multiple interface modules.

interface module	mapping module	description
echo	pipe	Demonstration interface used mostly for verification and testing purposes.
alsa	uncmp_audio	Audio interface created for demonstration on Linux. Can be used to play captured (line in, mic) audio stream via EAVB
alsa	aaf_audio	Audio interface created for demonstration on Linux. Can be used to play captured (line in, mic) audio stream via EAVB
wav_file	uncmp_audio	Configuration for playing wave file via EAVB

Interface and Mapping Module Configuration

Each interface module and mapping module has unique configuration values. Details of these configuration values can be found in the reference pages for each module.

Reference: AVTP Mapping Modules
Reference: AVTP Interface Module
Reference: AVTP Interface Module Linux Specific