ac97: introduce first AC'97 decoder implementation (bits, slots, binary)

Introduce an "audio and modem control for PC systems" protocol decoder
(referred to as AC'97).

This implementation extracts bits and identifies frames, and annotates
the slots of a frame with mere integer values. Bit fields get decoded
depending on the slot numbers. Bit patterns in audio/modem data slots
can get exported as binary streams.

Some TODO items remain. Register access (read/write) gets annotated, but
neither gets interpreted nor affects the decoding of subsequent frames.
The RESET# line status does not get evaluated.

1 files changed, 36 insertions, 0 deletions

diff --git a/decoders/ac97/__init__.py b/decoders/ac97/__init__.py
new file mode 100644
index 0000000..8b96e8a
--- /dev/null
+++ b/decoders/ac97/__init__.py
@@ -0,0 +1,36 @@
+##
+## This file is part of the libsigrokdecode project.
+##
+## Copyright (C) 2017 Gerhard Sittig <gerhard.sittig@gmx.net>
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 2 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; if not, see <http://www.gnu.org/licenses/>.
+##
+
+'''
+AC'97 (Audio Codec '97) was specifically designed by Intel for audio and
+modem I/O functionality in mainstream PC systems. See the specification in
+http://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf
+
+AC'97 communicates full duplex data (SDATA_IN, SDATA_OUT), where bits
+are clocked by the BIT_CLK and frames are signalled by the SYNC signals.
+A low active RESET# line completes the set of signals.
+
+Frames repeat at a nominal frequency of 48kHz, and consist of 256 bits
+each. One 16bit slot contains management information, twelve 20bit slots
+follow which carry data for three management and nine audio/modem channels.
+Optionally two slots of one frame can get combined for higher resolution
+on fewer channels, or double data rate.
+'''
+
+from .pd import Decoder