ieee488: introduce unified IEEE-488 decoder (supports GPIB and IEC)

Introduce an 'ieee488' protocol decoder which handles both the 16 lines
parallel GPIB variant as well as the serial IEC bus variant. Which kind
of supersedes the 'gpib' and 'iec' decoders.

This implementation increases maintainability because only the extraction
of raw bytes from the parallel or serial bus is separate, and all GPIB
related command/address/data interpretation is shared. This decoder extends
the feature set of the previous versions: Visual annotations are more fine
grained (more classes, additional rows, various text lengths to maintain
usability during zoom). There is binary output for communicated data,
as well as Python output for stacked decoders. Consecutive runs of
talker data gets accumulated, and is made available in binary form as well
as text (with escapes for non-printables). The terse single-letter format
(character codes '0' to 'O' for addresses) is kept for compatibility for
those users who are accustomed to it. The implemented logic also copes
with captures of low samplerate, where edges happen to fall onto the same
sample number which at higher samplerates shall be perceived as distant
and should get processed in their respective order of appearance.

This implementation tracks the most recent configuration of "peers" (the
set of talkers and listeners). A future implementation might support the
isolation of a single conversation out of a busy chat on the bus.

Some optional support for Commodore peripherals is included (currently
limited to disk channels), while it's recommended to move this logic to
a stacked decoder if it grows more complex.

2 files changed, 747 insertions, 0 deletions

diff --git a/decoders/ieee488/__init__.py b/decoders/ieee488/__init__.py
new file mode 100644
index 0000000..4240114
--- /dev/null
+++ b/decoders/ieee488/__init__.py
@@ -0,0 +1,26 @@
+##
+## This file is part of the libsigrokdecode project.
+##
+## Copyright (C) 2019 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 protocol decoder can decode the GPIB (IEEE-488) protocol. Both variants
+of (up to) 16 parallel lines as well as serial communication (IEC bus) are
+supported in this implementation.
+'''
+
+from .pd import Decoder
diff --git a/decoders/ieee488/pd.py b/decoders/ieee488/pd.py
new file mode 100644
index 0000000..5c25c66
--- /dev/null
+++ b/decoders/ieee488/pd.py
@@ -0,0 +1,721 @@
+##
+## This file is part of the libsigrokdecode project.
+##
+## Copyright (C) 2016 Rudolf Reuter <reuterru@arcor.de>
+## Copyright (C) 2017 Marcus Comstedt <marcus@mc.pp.se>
+## Copyright (C) 2019 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 file was created from earlier implementations of the 'gpib' and
+# the 'iec' protocol decoders. It combines the parallel and the serial
+# transmission variants in a single instance with optional inputs for
+# maximum code re-use.
+
+# TODO
+# - Extend annotations for improved usability.
+#   - Keep talkers' data streams on separate annotation rows? Is this useful
+#     here at the GPIB level, or shall stacked decoders dispatch these? May
+#     depend on how often captures get inspected which involve multiple peers.
+#   - Make serial bit annotations optional? Could slow down interactive
+#     exploration for long captures (see USB).
+# - Move the inlined Commodore IEC peripherals support to a stacked decoder
+#   when more peripherals get added.
+# - SCPI over GPIB may "represent somewhat naturally" here already when
+#   text lines are a single run of data at the GPIB layer (each line between
+#   the address spec and either EOI or ATN). So a stacked SCPI decoder may
+#   only become necessary when the text lines' content shall get inspected.
+
+import sigrokdecode as srd
+from common.srdhelper import bitpack
+
+'''
+OUTPUT_PYTHON format for stacked decoders:
+
+General packet format:
+[<ptype>, <addr>, <pdata>]
+
+This is the list of <ptype>s and their respective <pdata> values:
+
+Raw bits and bytes at the physical transport level:
+ - 'IEC_BIT': <addr> is not applicable, <pdata> is the transport's bit value.
+ - 'GPIB_RAW': <addr> is not applicable, <pdata> is the transport's
+   byte value. Data bytes are in the 0x00-0xff range, command/address
+   bytes are in the 0x100-0x1ff range.
+
+GPIB level byte fields (commands, addresses, pieces of data):
+ - 'COMMAND': <addr> is not applicable, <pdata> is the command's byte value.
+ - 'LISTEN': <addr> is the listener address (0-30), <pdata> is the raw
+   byte value (including the 0x20 offset).
+ - 'TALK': <addr> is the talker address (0-30), <pdata> is the raw byte
+   value (including the 0x40 offset).
+ - 'SECONDARY': <addr> is the secondary address (0-31), <pdata> is the
+   raw byte value (including the 0x60 offset).
+ - 'MSB_SET': <addr> as well as <pdata> are the raw byte value (including
+   the 0x80 offset). This usually does not happen for GPIB bytes with ATN
+   active, but was observed with the IEC bus and Commodore floppy drives,
+   when addressing channels within the device.
+ - 'DATA_BYTE': <addr> is the talker address (when available), <pdata>
+   is the raw data byte (transport layer, ATN inactive).
+
+Extracted payload information (peers and their communicated data):
+ - 'TALK_LISTEN': <addr> is the current talker, <pdata> is the list of
+   current listeners. These updates for the current "connected peers"
+   are sent when the set of peers changes, i.e. after talkers/listeners
+   got selected or deselected. Of course the data only covers what could
+   be gathered from the input data. Some controllers may not explicitly
+   address themselves, or captures may not include an early setup phase.
+ - 'TALKER_BYTES': <addr> is the talker address (when available), <pdata>
+   is the accumulated byte sequence between addressing a talker and EOI,
+   or the next command/address.
+ - 'TALKER_TEXT': <addr> is the talker address (when available), <pdata>
+   is the accumulated text sequence between addressing a talker and EOI,
+   or the next command/address.
+'''
+
+class ChannelError(Exception):
+    pass
+
+def _format_ann_texts(fmts, **args):
+    if not fmts:
+        return None
+    return [fmt.format(**args) for fmt in fmts]
+
+_cmd_table = {
+    # Command codes in the 0x00-0x1f range.
+    0x01: ['Go To Local', 'GTL'],
+    0x04: ['Selected Device Clear', 'SDC'],
+    0x05: ['Parallel Poll Configure', 'PPC'],
+    0x08: ['Global Execute Trigger', 'GET'],
+    0x09: ['Take Control', 'TCT'],
+    0x11: ['Local Lock Out', 'LLO'],
+    0x14: ['Device Clear', 'DCL'],
+    0x15: ['Parallel Poll Unconfigure', 'PPU'],
+    0x18: ['Serial Poll Enable', 'SPE'],
+    0x19: ['Serial Poll Disable', 'SPD'],
+    # Unknown type of command.
+    None: ['Unknown command 0x{cmd:02x}', 'command 0x{cmd:02x}', 'cmd {cmd:02x}', 'C{cmd_ord:c}'],
+    # Special listener/talker "addresses" (deselecting previous peers).
+    0x3f: ['Unlisten', 'UNL'],
+    0x5f: ['Untalk', 'UNT'],
+}
+
+def _is_command(b):
+    # Returns a tuple of booleans (or None when not applicable) whether
+    # the raw GPIB byte is: a command, an un-listen, an un-talk command.
+    if b in range(0x00, 0x20):
+        return True, None, None
+    if b in range(0x20, 0x40) and (b & 0x1f) == 31:
+        return True, True, False
+    if b in range(0x40, 0x60) and (b & 0x1f) == 31:
+        return True, False, True
+    return False, None, None
+
+def _is_listen_addr(b):
+    if b in range(0x20, 0x40):
+        return b & 0x1f
+    return None
+
+def _is_talk_addr(b):
+    if b in range(0x40, 0x60):
+        return b & 0x1f
+    return None
+
+def _is_secondary_addr(b):
+    if b in range(0x60, 0x80):
+        return b & 0x1f
+    return None
+
+def _is_msb_set(b):
+    if b & 0x80:
+        return b
+    return None
+
+def _get_raw_byte(b, atn):
+    # "Decorate" raw byte values for stacked decoders.
+    raw_byte = b
+    if atn:
+        raw_byte |= 0x100
+    return raw_byte
+
+def _get_raw_text(b, atn):
+    return ['{leader}{data:02x}'.format(leader = '/' if atn else '', data = b)]
+
+def _get_command_texts(b):
+    fmts = _cmd_table.get(b, None)
+    known = fmts is not None
+    if not fmts:
+        fmts = _cmd_table.get(None, None)
+    if not fmts:
+        return known, None
+    return known, _format_ann_texts(fmts, cmd = b, cmd_ord = ord('0') + b)
+
+def _get_address_texts(b):
+    laddr = _is_listen_addr(b)
+    taddr = _is_talk_addr(b)
+    saddr = _is_secondary_addr(b)
+    msb = _is_msb_set(b)
+    fmts = None
+    if laddr is not None:
+        fmts = ['Listen {addr:d}', 'L {addr:d}', 'L{addr_ord:c}']
+        addr = laddr
+    elif taddr is not None:
+        fmts = ['Talk {addr:d}', 'T {addr:d}', 'T{addr_ord:c}']
+        addr = taddr
+    elif saddr is not None:
+        fmts = ['Secondary {addr:d}', 'S {addr:d}', 'S{addr_ord:c}']
+        addr = saddr
+    elif msb is not None: # For IEC bus compat.
+        fmts = ['Secondary {addr:d}', 'S {addr:d}', 'S{addr_ord:c}']
+        addr = msb
+    return _format_ann_texts(fmts, addr = addr, addr_ord = ord('0') + addr)
+
+def _get_data_text(b):
+    # TODO Move the table of ASCII control characters to a common location?
+    # TODO Move the "printable with escapes" logic to a common helper?
+    _control_codes = {
+        0x00: 'NUL',
+        0x01: 'SOH',
+        0x02: 'STX',
+        0x03: 'ETX',
+        0x04: 'EOT',
+        0x05: 'ENQ',
+        0x06: 'ACK',
+        0x07: 'BEL',
+        0x08: 'BS',
+        0x09: 'TAB',
+        0x0a: 'LF',
+        0x0b: 'VT',
+        0x0c: 'FF',
+        0x0d: 'CR',
+        0x0e: 'SO',
+        0x0f: 'SI',
+        0x10: 'DLE',
+        0x11: 'DC1',
+        0x12: 'DC2',
+        0x13: 'DC3',
+        0x14: 'DC4',
+        0x15: 'NAK',
+        0x16: 'SYN',
+        0x17: 'ETB',
+        0x18: 'CAN',
+        0x19: 'EM',
+        0x1a: 'SUB',
+        0x1b: 'ESC',
+        0x1c: 'FS',
+        0x1d: 'GS',
+        0x1e: 'RS',
+        0x1f: 'US',
+    }
+    # Yes, exclude 0x7f (DEL) here. It's considered non-printable.
+    if b in range(0x20, 0x7f) and b not in ('[', ']'):
+        return '{:s}'.format(chr(b))
+    elif b in _control_codes:
+        return '[{:s}]'.format(_control_codes[b])
+    # Use a compact yet readable and unambigous presentation for bytes
+    # which contain non-printables. The format that is used here is
+    # compatible with 93xx EEPROM and UART decoders.
+    return '[{:02x}]'.format(b)
+
+(
+    PIN_DIO1, PIN_DIO2, PIN_DIO3, PIN_DIO4,
+    PIN_DIO5, PIN_DIO6, PIN_DIO7, PIN_DIO8,
+    PIN_EOI, PIN_DAV, PIN_NRFD, PIN_NDAC,
+    PIN_IFC, PIN_SRQ, PIN_ATN, PIN_REN,
+    PIN_CLK,
+) = range(17)
+PIN_DATA = PIN_DIO1
+
+(
+    ANN_RAW_BIT, ANN_RAW_BYTE,
+    ANN_CMD, ANN_LADDR, ANN_TADDR, ANN_SADDR, ANN_DATA,
+    ANN_EOI,
+    ANN_TEXT,
+    # TODO Want to provide one annotation class per talker address (0-30)?
+    ANN_IEC_PERIPH,
+    ANN_WARN,
+) = range(11)
+
+(
+    BIN_RAW,
+    BIN_DATA,
+    # TODO Want to provide one binary annotation class per talker address (0-30)?
+) = range(2)
+
+class Decoder(srd.Decoder):
+    api_version = 3
+    id = 'ieee488'
+    name = 'IEEE-488'
+    longname = 'General Purpose Interface Bus'
+    desc = 'IEEE-488 General Purpose Interface Bus (GPIB/HPIB or IEC).'
+    license = 'gplv2+'
+    inputs = ['logic']
+    outputs = ['ieee488']
+    tags = ['PC', 'Retro computing']
+    channels = (
+        {'id': 'dio1' , 'name': 'DIO1/DATA',
+            'desc': 'Data I/O bit 1, or serial data'},
+    )
+    optional_channels = (
+        {'id': 'dio2' , 'name': 'DIO2', 'desc': 'Data I/O bit 2'},
+        {'id': 'dio3' , 'name': 'DIO3', 'desc': 'Data I/O bit 3'},
+        {'id': 'dio4' , 'name': 'DIO4', 'desc': 'Data I/O bit 4'},
+        {'id': 'dio5' , 'name': 'DIO5', 'desc': 'Data I/O bit 5'},
+        {'id': 'dio6' , 'name': 'DIO6', 'desc': 'Data I/O bit 6'},
+        {'id': 'dio7' , 'name': 'DIO7', 'desc': 'Data I/O bit 7'},
+        {'id': 'dio8' , 'name': 'DIO8', 'desc': 'Data I/O bit 8'},
+        {'id': 'eoi', 'name': 'EOI', 'desc': 'End or identify'},
+        {'id': 'dav', 'name': 'DAV', 'desc': 'Data valid'},
+        {'id': 'nrfd', 'name': 'NRFD', 'desc': 'Not ready for data'},
+        {'id': 'ndac', 'name': 'NDAC', 'desc': 'Not data accepted'},
+        {'id': 'ifc', 'name': 'IFC', 'desc': 'Interface clear'},
+        {'id': 'srq', 'name': 'SRQ', 'desc': 'Service request'},
+        {'id': 'atn', 'name': 'ATN', 'desc': 'Attention'},
+        {'id': 'ren', 'name': 'REN', 'desc': 'Remote enable'},
+        {'id': 'clk', 'name': 'CLK', 'desc': 'Serial clock'},
+    )
+    options = (
+        {'id': 'iec_periph', 'desc': 'Decode Commodore IEC bus peripherals details',
+            'default': 'no', 'values': ('no', 'yes')},
+    )
+    annotations = (
+        ('bit', 'IEC bit'),
+        ('raw', 'Raw byte'),
+        ('cmd', 'Command'),
+        ('laddr', 'Listener address'),
+        ('taddr', 'Talker address'),
+        ('saddr', 'Secondary address'),
+        ('data', 'Data byte'),
+        ('eoi', 'EOI'),
+        ('text', 'Talker text'),
+        ('periph', 'IEC bus peripherals'),
+        ('warn', 'Warning'),
+    )
+    annotation_rows = (
+        ('bits', 'IEC bits', (ANN_RAW_BIT,)),
+        ('raws', 'Raw bytes', (ANN_RAW_BYTE,)),
+        ('gpib', 'Commands/data', (ANN_CMD, ANN_LADDR, ANN_TADDR, ANN_SADDR, ANN_DATA,)),
+        ('eois', 'EOI', (ANN_EOI,)),
+        ('texts', 'Talker texts', (ANN_TEXT,)),
+        ('periphs', 'IEC peripherals', (ANN_IEC_PERIPH,)),
+        ('warns', 'Warnings', (ANN_WARN,)),
+    )
+    binary = (
+        ('raw', 'Raw bytes'),
+        ('data', 'Talker bytes'),
+    )
+
+    def __init__(self):
+        self.reset()
+
+    def reset(self):
+        self.curr_raw = None
+        self.curr_atn = None
+        self.curr_eoi = None
+        self.latch_atn = None
+        self.latch_eoi = None
+        self.accu_bytes = []
+        self.accu_text = []
+        self.ss_raw = None
+        self.es_raw = None
+        self.ss_eoi = None
+        self.es_eoi = None
+        self.ss_text = None
+        self.es_text = None
+        self.last_talker = None
+        self.last_listener = []
+        self.last_iec_addr = None
+        self.last_iec_sec = None
+
+    def start(self):
+        self.out_ann = self.register(srd.OUTPUT_ANN)
+        self.out_bin = self.register(srd.OUTPUT_BINARY)
+        self.out_python = self.register(srd.OUTPUT_PYTHON)
+
+    def putg(self, ss, es, data):
+        self.put(ss, es, self.out_ann, data)
+
+    def putbin(self, ss, es, data):
+        self.put(ss, es, self.out_bin, data)
+
+    def putpy(self, ss, es, ptype, addr, pdata):
+        self.put(ss, es, self.out_python, [ptype, addr, pdata])
+
+    def emit_eoi_ann(self, ss, es):
+        self.putg(ss, es, [ANN_EOI, ['EOI']])
+
+    def emit_bin_ann(self, ss, es, ann_cls, data):
+        self.putbin(ss, es, [ann_cls, bytes(data)])
+
+    def emit_data_ann(self, ss, es, ann_cls, data):
+        self.putg(ss, es, [ann_cls, data])
+
+    def emit_warn_ann(self, ss, es, data):
+        self.putg(ss, es, [ANN_WARN, data])
+
+    def flush_bytes_text_accu(self):
+        if self.accu_bytes and self.ss_text is not None and self.es_text is not None:
+            self.emit_bin_ann(self.ss_text, self.es_text, BIN_DATA, bytearray(self.accu_bytes))
+            self.putpy(self.ss_text, self.es_text, 'TALKER_BYTES', self.last_talker, bytearray(self.accu_bytes))
+            self.accu_bytes = []
+        if self.accu_text and self.ss_text is not None and self.es_text is not None:
+            text = ''.join(self.accu_text)
+            self.emit_data_ann(self.ss_text, self.es_text, ANN_TEXT, [text])
+            self.putpy(self.ss_text, self.es_text, 'TALKER_TEXT', self.last_talker, text)
+            self.accu_text = []
+        self.ss_text = self.es_text = None
+
+    def handle_ifc_change(self, ifc):
+        # Track IFC line for parallel input.
+        # Assertion of IFC de-selects all talkers and listeners.
+        if ifc:
+            self.last_talker = None
+            self.last_listener = []
+
+    def handle_eoi_change(self, eoi):
+        # Track EOI line for parallel and serial input.
+        if eoi:
+            self.ss_eoi = self.samplenum
+            self.curr_eoi = eoi
+        else:
+            self.es_eoi = self.samplenum
+            if self.ss_eoi and self.latch_eoi:
+               self.emit_eoi_ann(self.ss_eoi, self.es_eoi)
+            self.es_text = self.es_eoi
+            self.flush_bytes_text_accu()
+            self.ss_eoi = self.es_eoi = None
+            self.curr_eoi = None
+
+    def handle_atn_change(self, atn):
+        # Track ATN line for parallel and serial input.
+        self.curr_atn = atn
+        if atn:
+            self.flush_bytes_text_accu()
+
+    def handle_iec_periph(self, ss, es, addr, sec, data):
+        # The annotation is optional.
+        if self.options['iec_periph'] != 'yes':
+            return
+        # Void internal state.
+        if addr is None and sec is None and data is None:
+            self.last_iec_addr = None
+            self.last_iec_sec = None
+            return
+        # Grab and evaluate new input.
+        _iec_addr_names = {
+            # TODO Add more items here. See the "Device numbering" section
+            # of the https://en.wikipedia.org/wiki/Commodore_bus page.
+            8: 'Disk 0',
+            9: 'Disk 1',
+        }
+        _iec_disk_range = range(8, 16)
+        if addr is not None:
+            self.last_iec_addr = addr
+            name = _iec_addr_names.get(addr, None)
+            if name:
+                self.emit_data_ann(ss, es, ANN_IEC_PERIPH, [name])
+        addr = self.last_iec_addr # Simplify subsequent logic.
+        if sec is not None:
+            # BEWARE! The secondary address is a full byte and includes
+            # the 0x60 offset, to also work when the MSB was set.
+            self.last_iec_sec = sec
+            subcmd, channel = sec & 0xf0, sec & 0x0f
+            channel_ord = ord('0') + channel
+            if addr is not None and addr in _iec_disk_range:
+                subcmd_fmts = {
+                    0x60: ['Reopen {ch:d}', 'Re {ch:d}', 'R{ch_ord:c}'],
+                    0xe0: ['Close {ch:d}', 'Cl {ch:d}', 'C{ch_ord:c}'],
+                    0xf0: ['Open {ch:d}', 'Op {ch:d}', 'O{ch_ord:c}'],
+                }.get(subcmd, None)
+                if subcmd_fmts:
+                    texts = _format_ann_texts(subcmd_fmts, ch = channel, ch_ord = channel_ord)
+                    self.emit_data_ann(ss, es, ANN_IEC_PERIPH, texts)
+        sec = self.last_iec_sec # Simplify subsequent logic.
+        if data is not None:
+            if addr is None or sec is None:
+                return
+            # TODO Process data depending on peripheral type and channel?
+
+    def handle_data_byte(self):
+        b = self.curr_raw
+        texts = _get_raw_text(b, self.curr_atn)
+        self.emit_data_ann(self.ss_raw, self.es_raw, ANN_RAW_BYTE, texts)
+        self.emit_bin_ann(self.ss_raw, self.es_raw, BIN_RAW, b.to_bytes(1, byteorder='big'))
+        self.putpy(self.ss_raw, self.es_raw, 'GPIB_RAW', None, _get_raw_byte(b, self.curr_atn))
+        if self.curr_atn:
+            ann_cls = None
+            upd_iec = False,
+            py_type = None
+            py_peers = False
+            is_cmd, is_unl, is_unt = _is_command(b)
+            laddr = _is_listen_addr(b)
+            taddr = _is_talk_addr(b)
+            saddr = _is_secondary_addr(b)
+            msb = _is_msb_set(b)
+            if is_cmd:
+                known, texts = _get_command_texts(b)
+                if not known:
+                    warn_texts = ['Unknown GPIB command', 'unknown', 'UNK']
+                    self.emit_warn_ann(self.ss_raw, self.es_raw, warn_texts)
+                ann_cls = ANN_CMD
+                py_type, py_addr = 'COMMAND', None
+                if is_unl:
+                    self.last_listener = []
+                    py_peers = True
+                if is_unt:
+                    self.last_talker = None
+                    py_peers = True
+                if is_unl or is_unt:
+                    upd_iec = True, None, None, None
+            elif laddr is not None:
+                addr = laddr
+                texts = _get_address_texts(b)
+                ann_cls = ANN_LADDR
+                py_type, py_addr = 'LISTEN', addr
+                if addr == self.last_talker:
+                    self.last_talker = None
+                self.last_listener.append(addr)
+                upd_iec = True, addr, None, None
+                py_peers = True
+            elif taddr is not None:
+                addr = taddr
+                texts = _get_address_texts(b)
+                ann_cls = ANN_TADDR
+                py_type, py_addr = 'TALK', addr
+                if addr in self.last_listener:
+                    self.last_listener.remove(addr)
+                self.last_talker = addr
+                upd_iec = True, addr, None, None
+                py_peers = True
+            elif saddr is not None:
+                addr = saddr
+                texts = _get_address_texts(b)
+                ann_cls = ANN_SADDR
+                upd_iec = True, None, b, None
+                py_type, py_addr = 'SECONDARY', addr
+            elif msb is not None:
+                # These are not really "secondary addresses", but they
+                # are used by the Commodore IEC bus (floppy channels).
+                texts = _get_address_texts(b)
+                ann_cls = ANN_SADDR
+                upd_iec = True, None, b, None
+                py_type, py_addr = 'MSB_SET', b
+            if ann_cls is not None and texts is not None:
+                self.emit_data_ann(self.ss_raw, self.es_raw, ann_cls, texts)
+            if upd_iec[0]:
+                self.handle_iec_periph(self.ss_raw, self.es_raw, upd_iec[1], upd_iec[2], upd_iec[3])
+            if py_type:
+                self.putpy(self.ss_raw, self.es_raw, py_type, py_addr, b)
+            if py_peers:
+                self.last_listener.sort()
+                self.putpy(self.ss_raw, self.es_raw, 'TALK_LISTEN', self.last_talker, self.last_listener)
+        else:
+            self.accu_bytes.append(b)
+            text = _get_data_text(b)
+            if not self.accu_text:
+                self.ss_text = self.ss_raw
+            self.accu_text.append(text)
+            self.es_text = self.es_raw
+            self.emit_data_ann(self.ss_raw, self.es_raw, ANN_DATA, [text])
+            self.handle_iec_periph(self.ss_raw, self.es_raw, None, None, b)
+            self.putpy(self.ss_raw, self.es_raw, 'DATA_BYTE', self.last_talker, b)
+
+    def handle_dav_change(self, dav, data):
+        if dav:
+            # Data availability starts when the flag goes active.
+            self.ss_raw = self.samplenum
+            self.curr_raw = bitpack(data)
+            self.latch_atn = self.curr_atn
+            self.latch_eoi = self.curr_eoi
+            return
+        # Data availability ends when the flag goes inactive. Handle the
+        # previously captured data byte according to associated flags.
+        self.es_raw = self.samplenum
+        self.handle_data_byte()
+        self.ss_raw = self.es_raw = None
+        self.curr_raw = None
+
+    def inject_dav_phase(self, ss, es, data):
+        # Inspection of serial input has resulted in one raw byte which
+        # spans a given period of time. Pretend we had seen a DAV active
+        # phase, to re-use code for the parallel transmission.
+        self.ss_raw = ss
+        self.curr_raw = bitpack(data)
+        self.latch_atn = self.curr_atn
+        self.latch_eoi = self.curr_eoi
+        self.es_raw = es
+        self.handle_data_byte()
+        self.ss_raw = self.es_raw = None
+        self.curr_raw = None
+
+    def invert_pins(self, pins):
+        # All lines (including data bits!) are low active and thus need
+        # to get inverted to receive their logical state (high active,
+        # regular data bit values). Cope with inputs being optional.
+        return [1 - p if p in (0, 1) else p for p in pins]
+
+    def decode_serial(self, has_clk, has_data_1, has_atn, has_srq):
+        if not has_clk or not has_data_1 or not has_atn:
+            raise ChannelError('IEC bus needs at least ATN and serial CLK and DATA.')
+
+        # This is a rephrased version of decoders/iec/pd.py:decode().
+        # SRQ was not used there either. Magic numbers were eliminated.
+        (
+            STEP_WAIT_READY_TO_SEND,
+            STEP_WAIT_READY_FOR_DATA,
+            STEP_PREP_DATA_TEST_EOI,
+            STEP_CLOCK_DATA_BITS,
+        ) = range(4)
+        step_wait_conds = (
+            [{PIN_ATN: 'f'}, {PIN_DATA: 'l', PIN_CLK: 'h'}],
+            [{PIN_ATN: 'f'}, {PIN_DATA: 'h', PIN_CLK: 'h'}, {PIN_CLK: 'l'}],
+            [{PIN_ATN: 'f'}, {PIN_DATA: 'f'}, {PIN_CLK: 'l'}],
+            [{PIN_ATN: 'f'}, {PIN_CLK: 'e'}],
+        )
+        step = STEP_WAIT_READY_TO_SEND
+        bits = []
+
+        while True:
+
+            # Sample input pin values. Keep DATA/CLK in verbatim form to
+            # re-use 'iec' decoder logic. Turn ATN to positive logic for
+            # easier processing. The data bits get handled during byte
+            # accumulation.
+            pins = self.wait(step_wait_conds[step])
+            data, clk = pins[PIN_DATA], pins[PIN_CLK]
+            atn, = self.invert_pins([pins[PIN_ATN]])
+
+            if self.matched[0]:
+                # Falling edge on ATN, reset step.
+                step = STEP_WAIT_READY_TO_SEND
+
+            if step == STEP_WAIT_READY_TO_SEND:
+                # Don't use self.matched[1] here since we might come from
+                # a step with different conds due to the code above.
+                if data == 0 and clk == 1:
+                    # Rising edge on CLK while DATA is low: Ready to send.
+                    step = STEP_WAIT_READY_FOR_DATA
+            elif step == STEP_WAIT_READY_FOR_DATA:
+                if data == 1 and clk == 1:
+                    # Rising edge on DATA while CLK is high: Ready for data.
+                    ss_byte = self.samplenum
+                    self.handle_atn_change(atn)
+                    if self.curr_eoi:
+                        self.handle_eoi_change(False)
+                    bits = []
+                    step = STEP_PREP_DATA_TEST_EOI
+                elif clk == 0:
+                    # CLK low again, transfer aborted.
+                    step = STEP_WAIT_READY_TO_SEND
+            elif step == STEP_PREP_DATA_TEST_EOI:
+                if data == 0 and clk == 1:
+                    # DATA goes low while CLK is still high, EOI confirmed.
+                    self.handle_eoi_change(True)
+                elif clk == 0:
+                    step = STEP_CLOCK_DATA_BITS
+                    ss_bit = self.samplenum
+            elif step == STEP_CLOCK_DATA_BITS:
+                if self.matched[1]:
+                    if clk == 1:
+                        # Rising edge on CLK; latch DATA.
+                        bits.append(data)
+                    elif clk == 0:
+                        # Falling edge on CLK; end of bit.
+                        es_bit = self.samplenum
+                        self.emit_data_ann(ss_bit, es_bit, ANN_RAW_BIT, ['{:d}'.format(bits[-1])])
+                        self.putpy(ss_bit, es_bit, 'IEC_BIT', None, bits[-1])
+                        ss_bit = self.samplenum
+                        if len(bits) == 8:
+                            es_byte = self.samplenum
+                            self.inject_dav_phase(ss_byte, es_byte, bits)
+                            if self.curr_eoi:
+                                self.handle_eoi_change(False)
+                            step = STEP_WAIT_READY_TO_SEND
+
+    def decode_parallel(self, has_data_n, has_dav, has_atn, has_eoi, has_srq):
+
+        if False in has_data_n or not has_dav or not has_atn:
+            raise ChannelError('IEEE-488 needs at least ATN and DAV and eight DIO lines.')
+        has_ifc = self.has_channel(PIN_IFC)
+
+        # Capture data lines at the falling edge of DAV, process their
+        # values at rising DAV edge (when data validity ends). Also make
+        # sure to start inspection when the capture happens to start with
+        # low signal levels, i.e. won't include the initial falling edge.
+        # Scan for ATN/EOI edges as well (including the trick which works
+        # around initial pin state).
+        # Map low-active physical transport lines to positive logic here,
+        # to simplify logical inspection/decoding of communicated data,
+        # and to avoid redundancy and inconsistency in later code paths.
+        waitcond = []
+        idx_dav = len(waitcond)
+        waitcond.append({PIN_DAV: 'l'})
+        idx_atn = len(waitcond)
+        waitcond.append({PIN_ATN: 'l'})
+        idx_eoi = None
+        if has_eoi:
+            idx_eoi = len(waitcond)
+            waitcond.append({PIN_EOI: 'l'})
+        idx_ifc = None
+        if has_ifc:
+            idx_ifc = len(waitcond)
+            waitcond.append({PIN_IFC: 'l'})
+        while True:
+            pins = self.wait(waitcond)
+            pins = self.invert_pins(pins)
+
+            # BEWARE! Order of evaluation does matter. For low samplerate
+            # captures, many edges fall onto the same sample number. So
+            # we process active edges of flags early (before processing
+            # data bits), and inactive edges late (after data got processed).
+            if idx_ifc is not None and self.matched[idx_ifc] and pins[PIN_IFC] == 1:
+                self.handle_ifc_change(pins[PIN_IFC])
+            if idx_eoi is not None and self.matched[idx_eoi] and pins[PIN_EOI] == 1:
+                self.handle_eoi_change(pins[PIN_EOI])
+            if self.matched[idx_atn] and pins[PIN_ATN] == 1:
+                self.handle_atn_change(pins[PIN_ATN])
+            if self.matched[idx_dav]:
+                self.handle_dav_change(pins[PIN_DAV], pins[PIN_DIO1:PIN_DIO8 + 1])
+            if self.matched[idx_atn] and pins[PIN_ATN] == 0:
+                self.handle_atn_change(pins[PIN_ATN])
+            if idx_eoi is not None and self.matched[idx_eoi] and pins[PIN_EOI] == 0:
+                self.handle_eoi_change(pins[PIN_EOI])
+            if idx_ifc is not None and self.matched[idx_ifc] and pins[PIN_IFC] == 0:
+                self.handle_ifc_change(pins[PIN_IFC])
+
+            waitcond[idx_dav][PIN_DAV] = 'e'
+            waitcond[idx_atn][PIN_ATN] = 'e'
+            if has_eoi:
+                waitcond[idx_eoi][PIN_EOI] = 'e'
+            if has_ifc:
+                waitcond[idx_ifc][PIN_IFC] = 'e'
+
+    def decode(self):
+        # The decoder's boilerplate declares some of the input signals as
+        # optional, but only to support both serial and parallel variants.
+        # The CLK signal discriminates the two. For either variant some
+        # of the "optional" signals are not really optional for proper
+        # operation of the decoder. Check these conditions here.
+        has_clk = self.has_channel(PIN_CLK)
+        has_data_1 = self.has_channel(PIN_DIO1)
+        has_data_n = [bool(self.has_channel(pin) for pin in range(PIN_DIO1, PIN_DIO8 + 1))]
+        has_dav = self.has_channel(PIN_DAV)
+        has_atn = self.has_channel(PIN_ATN)
+        has_eoi = self.has_channel(PIN_EOI)
+        has_srq = self.has_channel(PIN_SRQ)
+        if has_clk:
+            self.decode_serial(has_clk, has_data_1, has_atn, has_srq)
+        else:
+            self.decode_parallel(has_data_n, has_dav, has_atn, has_eoi, has_srq)