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.

2 files changed, 539 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
diff --git a/decoders/ac97/pd.py b/decoders/ac97/pd.py
new file mode 100644
index 0000000..6cb7e93
--- /dev/null
+++ b/decoders/ac97/pd.py
@@ -0,0 +1,503 @@
+##
+## 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/>.
+##
+
+# This implementation is incomplete. TODO items:
+# - Support the optional RESET# pin, detect cold and warm reset.
+# - Split slot values into audio samples of their respective width and
+#   frequency (either on user provided parameters, or from inspection of
+#   decoded register access).
+
+import sigrokdecode as srd
+
+class ChannelError(Exception):
+    pass
+
+class Pins:
+    (SYNC, BIT_CLK, SDATA_OUT, SDATA_IN, RESET) = range(5)
+
+class Ann:
+    (
+        BITS_OUT, BITS_IN,
+        SLOT_OUT_RAW, SLOT_OUT_TAG, SLOT_OUT_ADDR, SLOT_OUT_DATA,
+        SLOT_OUT_03, SLOT_OUT_04, SLOT_OUT_05, SLOT_OUT_06,
+        SLOT_OUT_07, SLOT_OUT_08, SLOT_OUT_09, SLOT_OUT_10,
+        SLOT_OUT_11, SLOT_OUT_IO,
+        SLOT_IN_RAW, SLOT_IN_TAG, SLOT_IN_ADDR, SLOT_IN_DATA,
+        SLOT_IN_03, SLOT_IN_04, SLOT_IN_05, SLOT_IN_06,
+        SLOT_IN_07, SLOT_IN_08, SLOT_IN_09, SLOT_IN_10,
+        SLOT_IN_11, SLOT_IN_IO,
+        WARN, ERROR,
+    ) = range(32)
+    (
+        BIN_FRAME_OUT,
+        BIN_FRAME_IN,
+        BIN_SLOT_RAW_OUT,
+        BIN_SLOT_RAW_IN,
+    ) = range(4)
+
+class Decoder(srd.Decoder):
+    api_version = 3
+    id = 'ac97'
+    name = "AC '97"
+    longname = "Audio Codec '97"
+    desc = 'Audio and modem control for PC systems.'
+    license = 'gplv2+'
+    inputs = ['logic']
+    outputs = ['ac97']
+    channels = (
+        {'id': 'sync', 'name': 'SYNC', 'desc': 'Frame synchronization'},
+        {'id': 'clk', 'name': 'BIT_CLK', 'desc': 'Data bits clock'},
+    )
+    optional_channels = (
+        {'id': 'out', 'name': 'SDATA_OUT', 'desc': 'Data output'},
+        {'id': 'in', 'name': 'SDATA_IN', 'desc': 'Data input'},
+        {'id': 'rst', 'name': 'RESET#', 'desc': 'Reset line'},
+    )
+    annotations = (
+        ('bit-out', 'Output bits'),
+        ('bit-in', 'Input bits'),
+        ('slot-out-raw', 'Output raw value'),
+        ('slot-out-tag', 'Output TAG'),
+        ('slot-out-cmd-addr', 'Output command address'),
+        ('slot-out-cmd-data', 'Output command data'),
+        ('slot-out-03', 'Output slot 3'),
+        ('slot-out-04', 'Output slot 4'),
+        ('slot-out-05', 'Output slot 5'),
+        ('slot-out-06', 'Output slot 6'),
+        ('slot-out-07', 'Output slot 7'),
+        ('slot-out-08', 'Output slot 8'),
+        ('slot-out-09', 'Output slot 9'),
+        ('slot-out-10', 'Output slot 10'),
+        ('slot-out-11', 'Output slot 11'),
+        ('slot-out-io-ctrl', 'Output I/O control'),
+        ('slot-in-raw', 'Input raw value'),
+        ('slot-in-tag', 'Input TAG'),
+        ('slot-in-sts-addr', 'Input status address'),
+        ('slot-in-sts-data', 'Input status data'),
+        ('slot-in-03', 'Input slot 3'),
+        ('slot-in-04', 'Input slot 4'),
+        ('slot-in-05', 'Input slot 5'),
+        ('slot-in-06', 'Input slot 6'),
+        ('slot-in-07', 'Input slot 7'),
+        ('slot-in-08', 'Input slot 8'),
+        ('slot-in-09', 'Input slot 9'),
+        ('slot-in-10', 'Input slot 10'),
+        ('slot-in-11', 'Input slot 11'),
+        ('slot-in-io-sts', 'Input I/O status'),
+        # TODO: Add more annotation classes:
+        # TAG: 'ready', 'valid', 'id', 'rsv'
+        # CMD ADDR: 'r/w', 'addr', 'unused'
+        # CMD DATA: 'data', 'unused'
+        # 3-11: 'data', 'unused', 'double data'
+        ('warning', 'Warning'),
+        ('error', 'Error'),
+    )
+    annotation_rows = (
+        ('bits-out', 'Output bits', (Ann.BITS_OUT,)),
+        ('slots-out-raw', 'Output numbers', (Ann.SLOT_OUT_RAW,)),
+        ('slots-out', 'Output slots', (
+            Ann.SLOT_OUT_TAG, Ann.SLOT_OUT_ADDR, Ann.SLOT_OUT_DATA,
+            Ann.SLOT_OUT_03, Ann.SLOT_OUT_04, Ann.SLOT_OUT_05, Ann.SLOT_OUT_06,
+            Ann.SLOT_OUT_07, Ann.SLOT_OUT_08, Ann.SLOT_OUT_09, Ann.SLOT_OUT_10,
+            Ann.SLOT_OUT_11, Ann.SLOT_OUT_IO,)),
+        ('bits-in', 'Input bits', (Ann.BITS_IN,)),
+        ('slots-in-raw', 'Input numbers', (Ann.SLOT_IN_RAW,)),
+        ('slots-in', 'Input slots', (
+            Ann.SLOT_IN_TAG, Ann.SLOT_IN_ADDR, Ann.SLOT_IN_DATA,
+            Ann.SLOT_IN_03, Ann.SLOT_IN_04, Ann.SLOT_IN_05, Ann.SLOT_IN_06,
+            Ann.SLOT_IN_07, Ann.SLOT_IN_08, Ann.SLOT_IN_09, Ann.SLOT_IN_10,
+            Ann.SLOT_IN_11, Ann.SLOT_IN_IO,)),
+        ('warnings', 'Warnings', (Ann.WARN,)),
+        ('errors', 'Errors', (Ann.ERROR,)),
+    )
+    binary = (
+        ('frame-out', 'Frame bits, output data'),
+        ('frame-in', 'Frame bits, input data'),
+        ('slot-raw-out', 'Raw slot bits, output data'),
+        ('slot-raw-in', 'Raw slot bits, input data'),
+        # TODO: Which (other) binary classes to implement?
+        # - Are binary annotations per audio slot useful?
+        # - Assume 20bit per slot, in 24bit units? Or assume 16bit
+        #   audio samples? Observe register access and derive width
+        #   of the audio data? Dump channels 3-11 or 1-12?
+    )
+
+    def putx(self, ss, es, cls, data):
+        self.put(ss, es, self.out_ann, [cls, data])
+
+    def putf(self, frombit, bitcount, cls, data):
+        ss = self.frame_ss_list[frombit]
+        es = self.frame_ss_list[frombit + bitcount]
+        self.putx(ss, es, cls, data)
+
+    def putb(self, frombit, bitcount, cls, data):
+        ss = self.frame_ss_list[frombit]
+        es = self.frame_ss_list[frombit + bitcount]
+        self.put(ss, es, self.out_binary, [cls, data])
+
+    def __init__(self):
+        self.out_binary = None
+        self.out_ann = None
+        self.reset()
+
+    def reset(self):
+        self.frame_ss_list = None
+        self.frame_slot_lens = [0, 16] + [16 + 20 * i for i in range(1, 13)]
+        self.frame_total_bits = self.frame_slot_lens[-1]
+        self.handle_slots = {
+            0: self.handle_slot_00,
+            1: self.handle_slot_01,
+            2: self.handle_slot_02,
+        }
+
+    def start(self):
+        if not self.out_binary:
+            self.out_binary = self.register(srd.OUTPUT_BINARY)
+        if not self.out_ann:
+            self.out_ann = self.register(srd.OUTPUT_ANN)
+
+    def metadata(self, key, value):
+        if key == srd.SRD_CONF_SAMPLERATE:
+            self.samplerate = value
+
+    def bits_to_int(self, bits):
+        # Convert MSB-first bit sequence to integer value.
+        if not bits:
+            return 0
+        count = len(bits)
+        value = sum([2 ** (count - 1 - i) for i in range(count) if bits[i]])
+        return value
+
+    def bits_to_bin_ann(self, bits):
+        # Convert MSB-first bit sequence to binary annotation data.
+        # It's assumed that the number of bits does not (in useful ways)
+        # fit into an integer, and we need to create an array of bytes
+        # from the data afterwards, anyway. Hence the separate routine
+        # and the conversion of eight bits each.
+        out = []
+        count = len(bits)
+        while count > 0:
+            count -= 8
+            by, bits = bits[:8], bits[8:]
+            by = self.bits_to_int(by)
+            out.append(by)
+        out = bytes(out)
+        return out
+
+    def int_to_nibble_text(self, value, bitcount):
+        # Convert number to hex digits for given bit count.
+        digits = (bitcount + 3) // 4
+        text = '{{:0{:d}x}}'.format(digits).format(value)
+        return text
+
+    def get_bit_field(self, data, size, off, count):
+        shift = size - off - count
+        data >>= shift
+        mask = (1 << count) - 1
+        data &= mask
+        return data
+
+    def flush_frame_bits(self):
+        # Flush raw frame bits to binary annotation.
+        anncls = Ann.BIN_FRAME_OUT
+        data = self.frame_bits_out[:]
+        count = len(data)
+        data = self.bits_to_bin_ann(data)
+        self.putb(0, count, anncls, data)
+
+        anncls = Ann.BIN_FRAME_IN
+        data = self.frame_bits_in[:]
+        count = len(data)
+        data = self.bits_to_bin_ann(data)
+        self.putb(0, count, anncls, data)
+
+    def start_frame(self, ss):
+        # Mark the start of a frame.
+        if self.frame_ss_list:
+            # Flush bits if we had a frame before the frame which is
+            # starting here.
+            self.flush_frame_bits()
+        self.frame_ss_list = [ss]
+        self.frame_bits_out = []
+        self.frame_bits_in = []
+        self.frame_slot_data_out = []
+        self.frame_slot_data_in = []
+        self.have_slots = {True: None, False: None}
+
+    def handle_slot_dummy(self, slotidx, bitidx, bitcount, is_out, data):
+        # Handle slot x, default/fallback handler.
+        # Only process data of slots 1-12 when slot 0 says "valid".
+        if not self.have_slots[is_out]:
+            return
+        if not self.have_slots[is_out][slotidx]:
+            return
+
+        # Emit a naive annotation with just the data bits that we saw
+        # for the slot (hex nibbles for density). For audio data this
+        # can be good enough. Slots with special meaning should not end
+        # up calling the dummy handler.
+        text = self.int_to_nibble_text(data, bitcount)
+        anncls = Ann.SLOT_OUT_TAG if is_out else Ann.SLOT_IN_TAG
+        self.putf(bitidx, bitcount, anncls + slotidx, [text])
+
+        # Emit binary output for the data that is contained in slots
+        # which end up calling the default handler. This transparently
+        # should translate to "the slots with audio data", as other
+        # slots which contain management data should have their specific
+        # handler routines. In the present form, this approach might be
+        # good enough to get a (header-less) audio stream for typical
+        # setups where only line-in or line-out are in use.
+        #
+        # TODO: Improve this early prototype implementation. For now the
+        # decoder just exports the upper 16 bits of each audio channel
+        # that happens to be valid. For an improved implementation, it
+        # either takes user provided specs or more smarts like observing
+        # register access (if the capture includes it).
+        anncls = Ann.BIN_SLOT_RAW_OUT if is_out else Ann.BIN_SLOT_RAW_IN
+        data_bin = data >> 4
+        data_bin &= 0xffff
+        data_bin = data_bin.to_bytes(2, byteorder = 'big')
+        self.putb(bitidx, bitcount, anncls, data_bin)
+
+    def handle_slot_00(self, slotidx, bitidx, bitcount, is_out, data):
+        # Handle slot 0, TAG.
+        slotpos = self.frame_slot_lens[slotidx]
+        fieldoff = 0
+        anncls = Ann.SLOT_OUT_TAG if is_out else Ann.SLOT_IN_TAG
+
+        fieldlen = 1
+        ready = self.get_bit_field(data, bitcount, fieldoff, fieldlen)
+        text = ['READY: 1', 'READY', 'RDY', 'R'] if ready else ['ready: 0', 'rdy', '-']
+        self.putf(slotpos + fieldoff, fieldlen, anncls, text)
+        fieldoff += fieldlen
+
+        fieldlen = 12
+        valid = self.get_bit_field(data, bitcount, fieldoff, fieldlen)
+        text = ['VALID: {:3x}'.format(valid), '{:3x}'.format(valid)]
+        self.putf(slotpos + fieldoff, fieldlen, anncls, text)
+        have_slots = [True] + [False] * 12
+        for idx in range(12):
+            have_slots[idx + 1] = bool(valid & (1 << (11 - idx)))
+        self.have_slots[is_out] = have_slots
+        fieldoff += fieldlen
+
+        fieldlen = 1
+        rsv = self.get_bit_field(data, bitcount, fieldoff, fieldlen)
+        if rsv != 0:
+            text = ['reserved bit error', 'rsv error', 'rsv']
+            self.putf(slotpos + fieldoff, fieldlen, Ann.ERROR, text)
+        fieldoff += fieldlen
+
+        # TODO: Will input slot 0 have a Codec ID, or 3 reserved bits?
+        fieldlen = 2
+        codec = self.get_bit_field(data, bitcount, fieldoff, fieldlen)
+        text = ['CODEC: {:1x}'.format(codec), '{:1x}'.format(codec)]
+        self.putf(slotpos + fieldoff, fieldlen, anncls, text)
+        fieldoff += fieldlen
+
+    def handle_slot_01(self, slotidx, bitidx, bitcount, is_out, data):
+        # Handle slot 1, command/status address.
+        slotpos = self.frame_slot_lens[slotidx]
+        if not self.have_slots[is_out]:
+            return
+        if not self.have_slots[is_out][slotidx]:
+            return
+        fieldoff = 0
+        anncls = Ann.SLOT_OUT_TAG if is_out else Ann.SLOT_IN_TAG
+        anncls += slotidx
+
+        fieldlen = 1
+        if is_out:
+            is_read = self.get_bit_field(data, bitcount, fieldoff, fieldlen)
+            text = ['READ', 'RD', 'R'] if is_read else ['WRITE', 'WR', 'W']
+            self.putf(slotpos + fieldoff, fieldlen, anncls, text)
+            # TODO: Check for the "atomic" constraint? Some operations
+            # involve address _and_ data, which cannot be spread across
+            # several frames. Slot 0 and 1 _must_ be provided within the
+            # same frame (the test should occur in the handler for slot
+            # 2 of course, in slot 1 we don't know what will follow).
+        else:
+            rsv = self.get_bit_field(data, bitcount, fieldoff, fieldlen)
+            if rsv != 0:
+                text = ['reserved bit error', 'rsv error', 'rsv']
+                self.putf(slotpos + fieldoff, fieldlen, Ann.ERROR, text)
+        fieldoff += fieldlen
+
+        fieldlen = 7
+        regaddr = self.get_bit_field(data, bitcount, fieldoff, fieldlen)
+        # TODO: Present 0-63 or 0-126 as the address of the 16bit register?
+        text = ['ADDR: {:2x}'.format(regaddr), '{:2x}'.format(regaddr)]
+        self.putf(slotpos + fieldoff, fieldlen, anncls, text)
+        if regaddr & 0x01:
+            text = ['odd register address', 'odd reg addr', 'odd addr', 'odd']
+            self.putf(slotpos + fieldoff, fieldlen, Ann.ERROR, text)
+        fieldoff += fieldlen
+
+        # Strictly speaking there are 10 data request bits and 2 reserved
+        # bits for input slots, and 12 reserved bits for output slots. We
+        # test for 10 and 2 bits, to simplify the logic. Only in case of
+        # non-zero reserved bits for outputs this will result in "a little
+        # strange" an annotation. This is a cosmetic issue, we don't mind.
+        fieldlen = 10
+        reqdata = self.get_bit_field(data, bitcount, fieldoff, fieldlen)
+        if is_out and reqdata != 0:
+            text = ['reserved bit error', 'rsv error', 'rsv']
+            self.putf(slotpos + fieldoff, fieldlen, Ann.ERROR, text)
+        if not is_out:
+            text = ['REQ: {:3x}'.format(reqdata), '{:3x}'.format(reqdata)]
+            self.putf(slotpos + fieldoff, fieldlen, anncls, text)
+        fieldoff += fieldlen
+
+        fieldlen = 2
+        rsv = self.get_bit_field(data, bitcount, fieldoff, fieldlen)
+        if rsv != 0:
+            text = ['reserved bit error', 'rsv error', 'rsv']
+            self.putf(slotpos + fieldoff, fieldlen, Ann.ERROR, text)
+        fieldoff += fieldlen
+
+    def handle_slot_02(self, slotidx, bitidx, bitcount, is_out, data):
+        # Handle slot 2, command/status data.
+        slotpos = self.frame_slot_lens[slotidx]
+        if not self.have_slots[is_out]:
+            return
+        if not self.have_slots[is_out][slotidx]:
+            return
+        fieldoff = 0
+        anncls = Ann.SLOT_OUT_TAG if is_out else Ann.SLOT_IN_TAG
+        anncls += slotidx
+
+        fieldlen = 16
+        rwdata = self.get_bit_field(data, bitcount, fieldoff, fieldlen)
+        # TODO: Check for zero output data when the operation is a read.
+        # TODO: Check for the "atomic" constraint.
+        text = ['DATA: {:4x}'.format(rwdata), '{:4x}'.format(rwdata)]
+        self.putf(slotpos + fieldoff, fieldlen, anncls, text)
+        fieldoff += fieldlen
+
+        fieldlen = 4
+        rsv = self.get_bit_field(data, bitcount, fieldoff, fieldlen)
+        if rsv != 0:
+            text = ['reserved bits error', 'rsv error', 'rsv']
+            self.putf(slotpos + fieldoff, fieldlen, Ann.ERROR, text)
+        fieldoff += fieldlen
+
+    # TODO: Implement other slots.
+    # - 1: cmd/status addr (check status vs command)
+    # - 2: cmd/status data (check status vs command)
+    # - 3-11: audio out/in
+    # - 12: io control/status (modem GPIO(?))
+
+    def handle_slot(self, slotidx, data_out, data_in):
+        # Process a received slot of a frame.
+        func = self.handle_slots.get(slotidx, self.handle_slot_dummy)
+        bitidx = self.frame_slot_lens[slotidx]
+        bitcount = self.frame_slot_lens[slotidx + 1] - bitidx
+        if data_out is not None:
+            func(slotidx, bitidx, bitcount, True, data_out)
+        if data_in is not None:
+            func(slotidx, bitidx, bitcount, False, data_in)
+
+    def handle_bits(self, ss, es, bit_out, bit_in):
+        # Process a received pair of bits.
+        # Emit the bits' annotations. Only interpret the data when we
+        # are in a frame (have seen the start of the frame, and don't
+        # exceed the expected number of bits in a frame).
+        if bit_out is not None:
+            self.putx(ss, es, Ann.BITS_OUT, ['{:d}'.format(bit_out)])
+        if bit_in is not None:
+            self.putx(ss, es, Ann.BITS_IN, ['{:d}'.format(bit_in)])
+        if self.frame_ss_list is None:
+            return
+        self.frame_ss_list.append(es)
+        have_len = len(self.frame_ss_list) - 1
+        if have_len > self.frame_total_bits:
+            return
+
+        # Accumulate the bits within the frame, until one slot of the
+        # frame has become available.
+        slot_idx = 0
+        if bit_out is not None:
+            self.frame_bits_out.append(bit_out)
+            slot_idx = len(self.frame_slot_data_out)
+        if bit_in is not None:
+            self.frame_bits_in.append(bit_in)
+            slot_idx = len(self.frame_slot_data_in)
+        want_len = self.frame_slot_lens[slot_idx + 1]
+        if have_len != want_len:
+            return
+        prev_len = self.frame_slot_lens[slot_idx]
+
+        # Convert bits to integer values. This shall simplify extraction
+        # of bit fields in multiple other locations.
+        slot_data_out = None
+        if bit_out is not None:
+            slot_bits = self.frame_bits_out[prev_len:]
+            slot_data = self.bits_to_int(slot_bits)
+            self.frame_slot_data_out.append(slot_data)
+            slot_data_out = slot_data
+        slot_data_in = None
+        if bit_in is not None:
+            slot_bits = self.frame_bits_in[prev_len:]
+            slot_data = self.bits_to_int(slot_bits)
+            self.frame_slot_data_in.append(slot_data)
+            slot_data_in = slot_data
+
+        # Emit simple annotations for the integer values, until upper
+        # layer decode stages will be implemented.
+        slot_len = have_len - prev_len
+        slot_ss = self.frame_ss_list[prev_len]
+        slot_es = self.frame_ss_list[have_len]
+        if slot_data_out is not None:
+            slot_text = self.int_to_nibble_text(slot_data_out, slot_len)
+            self.putx(slot_ss, slot_es, Ann.SLOT_OUT_RAW, [slot_text])
+        if slot_data_in is not None:
+            slot_text = self.int_to_nibble_text(slot_data_in, slot_len)
+            self.putx(slot_ss, slot_es, Ann.SLOT_IN_RAW, [slot_text])
+
+        self.handle_slot(slot_idx, slot_data_out, slot_data_in)
+
+    def decode(self):
+        have_sdo = self.has_channel(Pins.SDATA_OUT)
+        have_sdi = self.has_channel(Pins.SDATA_IN)
+        if not have_sdo and not have_sdi:
+            raise ChannelError('Either SDATA_OUT or SDATA_IN (or both) are required.')
+        have_reset = self.has_channel(Pins.RESET)
+
+        # Data is sampled at falling CLK edges. Annotations need to span
+        # the period between rising edges. SYNC rises one cycle _before_
+        # the start of a frame. Grab the earliest SYNC sample we can get
+        # and advance to the start of a bit time. Then keep getting the
+        # samples and the end of all subsequent bit times.
+        prev_sync = [None, None, None]
+        pins = self.wait({Pins.BIT_CLK: 'e'})
+        if pins[Pins.BIT_CLK] == 0:
+            prev_sync[-1] = pins[Pins.SYNC]
+            pins = self.wait({Pins.BIT_CLK: 'r'})
+        bit_ss = self.samplenum
+        while True:
+            pins = self.wait({Pins.BIT_CLK: 'f'})
+            prev_sync.pop(0)
+            prev_sync.append(pins[Pins.SYNC])
+            self.wait({Pins.BIT_CLK: 'r'})
+            if prev_sync[0] == 0 and prev_sync[1] == 1:
+                self.start_frame(bit_ss)
+            self.handle_bits(bit_ss, self.samplenum,
+                    pins[Pins.SDATA_OUT] if have_sdo else None,
+                    pins[Pins.SDATA_IN] if have_sdi else None)
+            bit_ss = self.samplenum