The SpeakerBox audio peripheral is available for connection to the SpeakerBox Interface (SBI) port of most dbri equipped systems and provides an integral monaural speaker as well as stereo line out, stereo line in, stereo headphone, and monaural microphone connections. The headset output level is adequate to power most headphones, but may be too low for some external speakers. Powered speakers or an external amplifier may be used with both the headphone and line out ports.

SPARCstation LX systems have the Multimedia Codec integrated onto the CPU board of the machine thus giving users the option of using it or using a SpeakerBox plugged into the AUI/Audio port on the back panel. When using the "onboard" Codec, the microphone and headphone ports are located on the system back panel - there are no Line In or Line Out ports available for this configuration. In addition, the headphone and microphone ports do not have the input detection circuitry to determine whether or not there is currently headphones or a microphone plugged in. If a SpeakerBox is plugged in when the machine is first rebooted and reconfigured, or upon the first access of the audio device, it will be used, otherwise the onboard Codec will be used.

The Sun Microphone is recommended for normal desktop audio recording. When the Sun Microphone is used in conjunction with the SpeakerBox, the microphone battery is bypassed. Other audio sources may be recorded by connecting their line output to the SpeakerBox line input (audio sources may also be connected from their headphone output if the volume is adjusted properly).

The DBRI controller offers two Basic Rate ISDN (BRI) interfaces. One is a BRI Terminal Equipment (TE) interface and the other is a BRI Network Termination (NT) interface.

The NT connector is switched by a relay so that when system power is not available or when software is not accessing the NT port, the TE and NT connectors are electrically connected and devices plugged into the NT port will be on the same BRI passive bus.

The dbri device supports the audio formats listed in the following table. When the device is open for simultaneous play and record, the input and output data formats must match.

ISDN channels implement a subset of audio semantics. The preferred ioctls for querying or setting the format of a BRI channel are ISDN_GET_FORMAT, ISDN_SET_FORMAT, and ISDN_SET_CHANNEL. In particular, there is no audio format described in audio(7I) that covers HDLC or transparent data. The dbri driver maps HDLC and transparent data to AUDIO_ENCODING_NONE. ISDN D-channels are always configured for HDLC encoding of data. The programmer should interpret an encoding value of AUDIO_ENCODING_NONE as an indication that the fd is not being used to transfer audio data.

B-channels can be configured for mu-law (as in the Greek letter mu), A-law, or HDLC encoding of data. The mu-law and A-law formats are always at 8000 Hz, 8-bit, mono. Although a BRI H-channel is actually 16 bits wide at the physical layer and the 16-bit sample occurs at 8 kHz, the HDLC encoding always presents the data in 8-bit quantities. Therefore, 56 bit-per-second (bps), 64 bps, and 128 bps formats are all presented to the programmer as 8-bit wide, mono, AUDIO_ENCODING_NONE format streams at different sample rates. A line rate of 56kbps results in a 8-bit sample rate of 7000 Hz. If the bit stuffing and un-stuffing of HDLC were taken into account, the data rate would be slightly less.

For the sake of compatibility, AUDIO_GETINFO will return one of the following on a ISDN channel:

ISDN_GET_FORMAT will return one of the following for an ISDN channel:

In the previous table:

HDLC = ISDN_MODE_HDLC TRANS = ISDN_MODE_TRANSPARENT

Audio ports are not relevant to ISDN D or B channels.

The record.avail_ports and play.avail_ports fields of the audio_info structure report the available input and output ports. The dbri device supports two input ports, selected by setting the record.port field to either AUDIO_MICROPHONE or AUDIO_LINE_IN. The play.port field may be set to any combination of AUDIO_SPEAKER, AUDIO_HEADPHONE, and AUDIO_LINE_OUT by OR'ing the desired port names together. As noted above, when using the onboard Multimedia Codec on the SPARCstation LX, the Line In and Line Out ports are not available.

Since the dbri device manipulates buffers of audio data, at any given time the reported input and output sample counts will vary from the actual sample count by no more than the size of the buffers it is transferring. Programs should, in general, not rely on absolute accuracy of the play.samples and record.samples fields of the audio_info structure.

As described in audio(7I), it is possible to request asynchronous notification of changes in the state of an audio device. The DBRI driver extends this to the ISDN B channels by sending the signal up the data channel instead of the control channel. Asynchronous notification of events on a B-channel only occurs when the channel is in a transparent data mode. When the channel is in HDLC mode, no such notification will take place.