PA168/PA1688
This is chip solution, complete
with reference design and software that allows you to
make cheap phones.
The CPU is similar to an MCS8051 and operates at 50 MHz.
That is a 8bit CPU ...
to speed it up, it has an on-chip DSP which is ADSP2181
instruction set compatible, operating at 33 MHz. The
chip has interfaces to RS232, USB, SDRAM, SRAM, AC97
codec and a keypad. An RTL8019 10MBit ethernet chip can
easily be connected.
Part of the documentation is, as to be expected from a
Chinese product, gibberish:
Considering about standard MCS8051, there are a 256bits SRAM in core.
The most scope of core can seek is 65536bits of SRAM and 65536 of Program
Flash. There has a 4.5KB SRAM in PA1688, it is an outside SRAM of MCU core
seeked.
Now everything is indeed clear. :-)
Actually, this chipset has a number of nice features. It
comes with G.729/G.723.1 codecs. iLBC support will be
added in the next release. IAX2 support is under active
development. The voice prompts are available in a number
of languages (English and Mandarin are standard, French
or German or other custom language is available by
request).
Although the code is close source, it's pretty easy
(compared to most closed-source products) to get a copy
of the code. Even if you don't have access to the
source, the developers are willing to consider widely
useful enhancements - for intance I asked about uPnP
support, provided the developers with a link to libupnp
and they said they'd look into it. Ok, so maybe it will
be a while before it arrives, but any other group would
have given me the answer "order 200K items and we'll do
it" - no very useful for a small-time user.
It supports up to 5 seperate SIP registrars, but not
simultaneously (you can preset the phone to work with 5
providers, say, FWD and Stanaphone, but only one will
register at a time.It's fairly easy, however, to switch
among profiles/proxies). STUN servers are supported, but
not uPnP (yet).