Thanks to Phil Zimmermann for the code and for the license exception
we needed to include it.
There remains some build system integration work to be done before
this code will build properly in the FreeSWITCH tree.
Use the amount of audio data received in misdn_read() to determine how many
bytes we need to send to the b-channel (= how much free space is left
in the b-channel tx queue). (This is how libosmo-abis and LCR handle it too.)
A pipe is used as a poll()-able audio tx buffer (filled in misdn_write()):
FTDM_WRITE wait requests are currently poll()-ed on the input side of the pipe,
whereas FTDM_READ and _EVENT requests are poll()-ed on the b-channel socket itself.
For every N-bytes of audio data read from the b-channel in misdn_read(),
we try to get as much out of the tx pipe, convert it into the ISDN_P_B_RAW
format and send it to the b-channel socket.
If there's less than N-bytes left in the pipe, we fill the remaining buffer
with silence to avoid buffer underflows.
B-Channel handling overview:
- misdn_wait(FTDM_WRITE) on audio pipe
- misdn_write() put audio data into pipe
- misdn_wait(FTDM_READ) for next incoming mISDN
message on b-channel socket
- misdn_read() handle mISDN event, for PH_DATA_IND:
- Write data into channel buffer and convert
to a/u-law using misdn_convert_audio_bits()
- Try to fetch N-bytes from audio pipe
- If not enough bytes in pipe: fill remaining space with silence
- Convert audio to raw format
- Send to b-channel (PH_DATA_REQ)
Known problems / bugs / further investigation:
1. Bridge aborted by "Write Buffer 0 bytes Failed!" error from switch_core_io.c.
This is "fixed" by _not_ setting the b-channel sockfd to non-blocking mode.
2. Audio glitches (maybe caused by FTDM_WRITE misdn_wait() handling or blocking I/O on sockfd?)
3. misdn_read() EBUSY error messages from sending data to b-channel sockfd after enabling channel.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>
The former fixes a strange "bug" with hfcsusb, where a b-channel deactivation
on a inactive channel (caused by a reset cycle) would cause the port to
lock up and stop processing events.
NOTE: this still needs to be investigated further, but this workaround will
at least prevent it from breaking completely.
We'll now keep track of the channel activation state and not send any
PH_ACTIVATE_REQ / PH_DEACTIVATE_REQ requests, if the channel already has the
desired state.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>
Use POLLIN on the socket instead, the b-channel should be able
to write when there is something to read.
Several other projects handle it this way, e.g. libosmo-abis.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>
Anthony Minessale
Travis Cross
David Yat Sin
Steve Underwood
Stefan Knoblich
Ken Rice
Moises Silva
Jeff Lenk
Christopher Rienzo