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+$Id: README.audio,v 1.8 1999/07/11 17:17:29 armin Exp $
+
+ISDN subsystem for Linux.
+ Description of audio mode.
+
+When enabled during kernel configuration, the tty emulator of the ISDN
+subsystem is capable of a reduced set of commands to support audio.
+This document describes the commands supported and the format of
+audio data.
+
+Commands for enabling/disabling audio mode:
+
+ AT+FCLASS=8 Enable audio mode.
+ This affects the following registers:
+ S18: Bits 0 and 2 are set.
+ S16: Set to 48 and any further change to
+ larger values is blocked.
+ AT+FCLASS=0 Disable audio mode.
+ Register 18 is set to 4.
+ AT+FCLASS=? Show possible modes.
+ AT+FCLASS? Report current mode (0 or 8).
+
+Commands supported in audio mode:
+
+All audio mode commands have one of the following forms:
+
+ AT+Vxx? Show current setting.
+ AT+Vxx=? Show possible settings.
+ AT+Vxx=v Set simple parameter.
+ AT+Vxx=v,v ... Set complex parameter.
+
+where xx is a two-character code and v are alphanumerical parameters.
+The following commands are supported:
+
+ AT+VNH=x Auto hangup setting. NO EFFECT, supported
+ for compatibility only.
+ AT+VNH? Always reporting "1"
+ AT+VNH=? Always reporting "1"
+
+ AT+VIP Reset all audio parameters.
+
+ AT+VLS=x Line select. x is one of the following:
+ 0 = No device.
+ 2 = Phone line.
+ AT+VLS=? Always reporting "0,2"
+ AT+VLS? Show current line.
+
+ AT+VRX Start recording. Emulator responds with
+ CONNECT and starts sending audio data to
+ the application. See below for data format
+
+ AT+VSD=x,y Set silence-detection parameters.
+ Possible parameters:
+ x = 0 ... 31 sensitivity threshold level.
+ (default 0 , deactivated)
+ y = 0 ... 255 range of interval in units
+ of 0.1 second. (default 70)
+ AT+VSD=? Report possible parameters.
+ AT+VSD? Show current parameters.
+
+ AT+VDD=x,y Set DTMF-detection parameters.
+ Only possible if online and during this connection.
+ Possible parameters:
+ x = 0 ... 15 sensitivity threshold level.
+ (default 0 , I4L soft-decode)
+ (1-15 soft-decode off, hardware on)
+ y = 0 ... 255 tone duration in units of 5ms.
+ Not for I4L soft decode (default 8, 40ms)
+ AT+VDD=? Report possible parameters.
+ AT+VDD? Show current parameters.
+
+ AT+VSM=x Select audio data format.
+ Possible parameters:
+ 2 = ADPCM-2
+ 3 = ADPCM-3
+ 4 = ADPCM-4
+ 5 = aLAW
+ 6 = uLAW
+ AT+VSM=? Show possible audio formats.
+
+ AT+VTX Start audio playback. Emulator responds
+ with CONNECT and starts sending audio data
+ received from the application via phone line.
+General behavior and description of data formats/protocol.
+ when a connection is made:
+
+ On incoming calls, if the application responds to a RING
+ with ATA, depending on the calling service, the emulator
+ responds with either CONNECT (data call) or VCON (voice call).
+
+ On outgoing voice calls, the emulator responds with VCON
+ upon connection setup.
+
+ Audio recording.
+
+ When receiving audio data, a kind of bisync protocol is used.
+ Upon AT+VRX command, the emulator responds with CONNECT, and
+ starts sending audio data to the application. There are several
+ escape sequences defined, all using DLE (0x10) as Escape char:
+
+ <DLE><ETX> End of audio data. (i.e. caused by a
+ hangup of the remote side) Emulator stops
+ recording, responding with VCON.
+ <DLE><DC4> Abort recording, (send by appl.) Emulator
+ stops recording, sends DLE,ETX.
+ <DLE><DLE> Escape sequence for DLE in data stream.
+ <DLE>0 Touchtone "0" received.
+ ...
+ <DLE>9 Touchtone "9" received.
+ <DLE># Touchtone "#" received.
+ <DLE>* Touchtone "*" received.
+ <DLE>A Touchtone "A" received.
+ <DLE>B Touchtone "B" received.
+ <DLE>C Touchtone "C" received.
+ <DLE>D Touchtone "D" received.
+
+ <DLE>q quiet. Silence detected after non-silence.
+ <DLE>s silence. Silence detected from the
+ start of recording.
+
+ Currently unsupported DLE sequences:
+
+ <DLE>c FAX calling tone received.
+ <DLE>b busy tone received.
+
+ Audio playback.
+
+ When sending audio data, upon AT+VTX command, emulator responds with
+ CONNECT, and starts transferring data from application to the phone line.
+ The same DLE sequences apply to this mode.
+
+ Full-Duplex-Audio:
+
+ When _both_ commands for recording and playback are given in _one_
+ AT-command-line (i.e.: "AT+VTX+VRX"), full-duplex-mode is selected.
+ In this mode, the only way to stop recording is sending <DLE><DC4>
+ and the only way to stop playback is to send <DLE><ETX>.
+