--- /dev/null
+##
+## This file is part of the libsigrokdecode project.
+##
+## Copyright (C) 2020 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/>.
+##
+
+# See the https://www.pjon.org/ PJON project page and especially the
+# https://www.pjon.org/PJON-protocol-specification-v3.2.php protocol
+# specification, which can use different link layers.
+
+# TODO
+# - Handle RX and TX identifiers in separate routines, including the
+# optional bus identifers. Track those addresses, add formatters for
+# them, and emit "communication relation" details.
+# - Check for correct endianess in variable width fields. The spec says
+# "network order", that's what this implementation uses.
+# - Check for the correct order of optional fields (the spec is not as
+# explicit on these details as I'd expect).
+# - Check decoder's robustness, completeness, and correctness when more
+# captures become available. Currently there are only few, which only
+# cover minimal communication, and none of the protocol's flexibility.
+# The decoder was essentially written based on the available docs, and
+# then took some arbitrary choices and liberties to cope with real life
+# data from an example setup. Strictly speaking this decoder violates
+# the spec, and errs towards the usability side.
+
+import sigrokdecode as srd
+import struct
+
+ANN_RX_INFO, ANN_HDR_CFG, ANN_PKT_LEN, ANN_META_CRC, ANN_TX_INFO, \
+ANN_SVC_ID, ANN_PKT_ID, ANN_ANON_DATA, ANN_PAYLOAD, ANN_END_CRC, \
+ANN_SYN_RSP, \
+ANN_RELATION, \
+ANN_WARN, \
+ = range(13)
+
+def calc_crc8(data):
+ crc = 0
+ for b in data:
+ crc ^= b
+ for i in range(8):
+ odd = crc % 2
+ crc >>= 1
+ if odd:
+ crc ^= 0x97
+ return crc
+
+def calc_crc32(data):
+ crc = 0xffffffff
+ for b in data:
+ crc ^= b
+ for i in range(8):
+ odd = crc % 2
+ crc >>= 1
+ if odd:
+ crc ^= 0xedb88320
+ crc ^= 0xffffffff
+ return crc
+
+class Decoder(srd.Decoder):
+ api_version = 3
+ id = 'pjon'
+ name = 'PJON'
+ longname = 'PJON'
+ desc = 'The PJON protocol.'
+ license = 'gplv2+'
+ inputs = ['pjon-link']
+ outputs = []
+ tags = ['Embedded']
+ annotations = (
+ ('rx_info', 'Receiver ID'),
+ ('hdr_cfg', 'Header config'),
+ ('pkt_len', 'Packet length'),
+ ('meta_crc', 'Meta CRC'),
+ ('tx_info', 'Sender ID'),
+ ('port', 'Service ID'),
+ ('pkt_id', 'Packet ID'),
+ ('anon', 'Anonymous data'),
+ ('payload', 'Payload'),
+ ('end_crc', 'End CRC'),
+ ('syn_rsp', 'Sync response'),
+ ('relation', 'Relation'),
+ ('warning', 'Warning'),
+ )
+ annotation_rows = (
+ ('fields', 'Fields', (
+ ANN_RX_INFO, ANN_HDR_CFG, ANN_PKT_LEN, ANN_META_CRC, ANN_TX_INFO,
+ ANN_SVC_ID, ANN_ANON_DATA, ANN_PAYLOAD, ANN_END_CRC, ANN_SYN_RSP,
+ )),
+ ('relations', 'Relations', (ANN_RELATION,)),
+ ('warnings', 'Warnings', (ANN_WARN,)),
+ )
+
+ def __init__(self):
+ self.reset()
+
+ def reset(self):
+ self.reset_frame()
+
+ def reset_frame(self):
+ self.frame_bytes = None
+ self.ack_bytes = None
+ self.ann_ss = None
+ self.ann_es = None
+
+ def start(self):
+ self.out_ann = self.register(srd.OUTPUT_ANN)
+
+ def putg(self, ss, es, ann, data):
+ self.put(ss, es, self.out_ann, [ann, data])
+
+ def frame_flush(self):
+ if not self.frame_bytes:
+ return
+ # TODO Emit "communication relation" details here?
+
+ def handle_field_get_desc(self, idx = None):
+ '''Lookup description of a PJON frame field.'''
+ if not self.field_desc:
+ return None
+ if idx is None:
+ idx = self.field_desc_idx
+ if idx >= 0 and idx >= len(self.field_desc):
+ return None
+ if idx < 0 and abs(idx) > len(self.field_desc):
+ return None
+ desc = self.field_desc[idx]
+ return desc
+
+ def handle_field_add_desc(self, fmt, hdl, cls = None):
+ '''Register description for a PJON frame field.'''
+ item = {
+ 'format': fmt,
+ 'width': struct.calcsize(fmt),
+ 'handler': hdl,
+ 'anncls': cls,
+ }
+ self.field_desc.append(item)
+
+ def handle_field_seed_desc(self):
+ '''Seed list of PJON frame fields' descriptions.'''
+
+ # At the start of a PJON frame, the layout of only two fields
+ # is known. Subsequent fields (their presence, and width) depend
+ # on the content of the header config field.
+
+ self.field_desc = []
+ self.handle_field_add_desc('<B', self.handle_field_rx_id, ANN_RX_INFO)
+ self.handle_field_add_desc('<B', self.handle_field_config, ANN_HDR_CFG)
+
+ self.field_desc_idx = 0
+ self.field_desc_got = 0
+
+ self.frame_rx_id = None
+ self.frame_is_broadcast = None
+ self.frame_tx_id = None
+ self.frame_payload = None
+ self.frame_has_ack = None
+
+ def handle_field_rx_id(self, b):
+ '''Process receiver ID field of a PJON frame.'''
+
+ b = b[0]
+
+ # Track RX info for communication relation emission.
+ self.frame_rx_id = b
+ self.frame_is_broadcast = b == 0
+
+ # Provide text presentation, caller emits frame field annotation.
+ if b == 255: # "not assigned"
+ id_txt = 'NA'
+ elif b == 0: # "broadcast"
+ id_txt = 'BC'
+ else: # unicast
+ id_txt = '{:d}'.format(b)
+ texts = [
+ 'RX_ID {}'.format(id_txt),
+ '{}'.format(id_txt),
+ ]
+ return texts
+
+ def handle_field_config(self, b):
+ '''Process header config field of a PJON frame.'''
+
+ # Caller provides a list of values. We want a single scalar.
+ b = b[0]
+
+ # Get the config flags.
+ self.cfg_shared = b & (1 << 0)
+ self.cfg_tx_info = b & (1 << 1)
+ self.cfg_sync_ack = b & (1 << 2)
+ self.cfg_async_ack = b & (1 << 3)
+ self.cfg_port = b & (1 << 4)
+ self.cfg_crc32 = b & (1 << 5)
+ self.cfg_len16 = b & (1 << 6)
+ self.cfg_pkt_id = b & (1 << 7)
+
+ # Get a textual presentation of the flags.
+ text = []
+ text.append('pkt_id' if self.cfg_pkt_id else '-') # packet number
+ text.append('len16' if self.cfg_len16 else '-') # 16bit length not 8bit
+ text.append('crc32' if self.cfg_crc32 else '-') # 32bit CRC not 8bit
+ text.append('svc_id' if self.cfg_port else '-') # port aka service ID
+ text.append('ack_mode' if self.cfg_async_ack else '-') # async response
+ text.append('ack' if self.cfg_sync_ack else '-') # synchronous response
+ text.append('tx_info' if self.cfg_tx_info else '-')
+ text.append('bus_id' if self.cfg_shared else '-') # "shared" vs "local"
+ text = ' '.join(text)
+ bits = '{:08b}'.format(b)
+ texts = [
+ 'CFG {:s}'.format(text),
+ 'CFG {}'.format(bits),
+ bits
+ ]
+
+ # TODO Come up with the most appropriate phrases for this logic.
+ # Are separate instruction groups with repeated conditions more
+ # readable than one common block which registers fields _and_
+ # updates the overhead size? Or is the latter preferrable due to
+ # easier maintenance and less potential for inconsistency?
+
+ # Get the size of variable width fields, to calculate the size
+ # of the packet overhead (the part that is not the payload data).
+ # This lets us derive the payload length when we later receive
+ # the packet length.
+ u8_fmt = '>B'
+ u16_fmt = '>H'
+ u32_fmt = '>L'
+ len_fmt = u16_fmt if self.cfg_len16 else u8_fmt
+ crc_fmt = u32_fmt if self.cfg_crc32 else u8_fmt
+ self.cfg_overhead = 0
+ self.cfg_overhead += struct.calcsize(u8_fmt) # receiver ID
+ self.cfg_overhead += struct.calcsize(u8_fmt) # header config
+ self.cfg_overhead += struct.calcsize(len_fmt) # packet length
+ self.cfg_overhead += struct.calcsize(u8_fmt) # initial CRC, always CRC8
+ # TODO Check for completeness and correctness.
+ if self.cfg_shared:
+ self.cfg_overhead += struct.calcsize(u32_fmt) # receiver bus
+ if self.cfg_tx_info:
+ if self.cfg_shared:
+ self.cfg_overhead += struct.calcsize(u32_fmt) # sender bus
+ self.cfg_overhead += struct.calcsize(u8_fmt) # sender ID
+ if self.cfg_port:
+ self.cfg_overhead += struct.calcsize(u16_fmt) # service ID
+ if self.cfg_pkt_id:
+ self.cfg_overhead += struct.calcsize(u16_fmt) # packet ID
+ self.cfg_overhead += struct.calcsize(crc_fmt) # end CRC
+
+ # Register more frame fields as we learn about their presence and
+ # format. Up to this point only receiver ID and header config were
+ # registered since their layout is fixed.
+ #
+ # Packet length and meta CRC are always present but can be of
+ # variable width. Optional fields follow the meta CRC and preceed
+ # the payload bytes. Notice that payload length isn't known here
+ # either, though its position is known already. The packet length
+ # is yet to get received. Subtracting the packet overhead from it
+ # (which depends on the header configuration) will provide that
+ # information.
+ #
+ # TODO Check for completeness and correctness.
+ # TODO Optionally fold overhead size arith and field registration
+ # into one block of instructions, to reduce the redundancy in the
+ # condition checks, and raise awareness for incomplete sequences
+ # during maintenance.
+ self.handle_field_add_desc(len_fmt, self.handle_field_pkt_len, ANN_PKT_LEN)
+ self.handle_field_add_desc(u8_fmt, self.handle_field_init_crc, ANN_META_CRC)
+ if self.cfg_shared:
+ self.handle_field_add_desc(u32_fmt, ['RX_BUS {:08x}', '{:08x}'], ANN_ANON_DATA)
+ if self.cfg_tx_info:
+ if self.cfg_shared:
+ self.handle_field_add_desc(u32_fmt, ['TX_BUS {:08x}', '{:08x}'], ANN_ANON_DATA)
+ self.handle_field_add_desc(u8_fmt, ['TX_ID {:d}', '{:d}'], ANN_ANON_DATA)
+ if self.cfg_port:
+ self.handle_field_add_desc(u16_fmt, ['PORT {:d}', '{:d}'], ANN_ANON_DATA)
+ if self.cfg_pkt_id:
+ self.handle_field_add_desc(u16_fmt, ['PKT {:04x}', '{:04x}'], ANN_ANON_DATA)
+ pl_fmt = '>{:d}B'.format(0)
+ self.handle_field_add_desc(pl_fmt, self.handle_field_payload, ANN_PAYLOAD)
+ self.handle_field_add_desc(crc_fmt, self.handle_field_end_crc, ANN_END_CRC)
+
+ # Emit warning annotations for invalid flag combinations.
+ warn_texts = []
+ wants_ack = self.cfg_sync_ack or self.cfg_async_ack
+ if wants_ack and not self.cfg_tx_info:
+ warn_texts.append('ACK request without TX info')
+ if wants_ack and self.frame_is_broadcast:
+ warn_texts.append('ACK request for broadcast')
+ if self.cfg_sync_ack and self.cfg_async_ack:
+ warn_texts.append('sync and async ACK request')
+ if self.cfg_len16 and not self.cfg_crc32:
+ warn_texts.append('extended length needs CRC32')
+ if warn_texts:
+ warn_texts = ', '.join(warn_texts)
+ self.putg(self.ann_ss, self.ann_es, ANN_WARN, [warn_texts])
+
+ # Have the caller emit the annotation for configuration data.
+ return texts
+
+ def handle_field_pkt_len(self, b):
+ '''Process packet length field of a PJON frame.'''
+
+ # Caller provides a list of values. We want a single scalar.
+ b = b[0]
+
+ # The wire communicates the total packet length. Some of it is
+ # overhead (non-payload data), while its volume is variable in
+ # size (dpends on the header configuration).
+ #
+ # Derive the payload size from previously observed flags. Update
+ # the previously registered field description (the second last
+ # item in the list, before the end CRC).
+
+ pkt_len = b
+ pl_len = b - self.cfg_overhead
+ warn_texts = []
+ if pkt_len not in range(self.cfg_overhead, 65536):
+ warn_texts.append('suspicious packet length')
+ if pkt_len > 15 and not self.cfg_crc32:
+ warn_texts.append('length above 15 needs CRC32')
+ if pl_len < 1:
+ warn_texts.append('suspicious payload length')
+ pl_len = 0
+ if warn_texts:
+ warn_texts = ', '.join(warn_texts)
+ self.putg(self.ann_ss, self.ann_es, ANN_WARN, [warn_texts])
+ pl_fmt = '>{:d}B'.format(pl_len)
+
+ desc = self.handle_field_get_desc(-2)
+ desc['format'] = pl_fmt
+ desc['width'] = struct.calcsize(pl_fmt)
+
+ # Have the caller emit the annotation for the packet length.
+ # Provide information of different detail level for zooming.
+ texts = [
+ 'LENGTH {:d} (PAYLOAD {:d})'.format(pkt_len, pl_len),
+ 'LEN {:d} (PL {:d})'.format(pkt_len, pl_len),
+ '{:d} ({:d})'.format(pkt_len, pl_len),
+ '{:d}'.format(pkt_len),
+ ]
+ return texts
+
+ def handle_field_common_crc(self, have, is_meta):
+ '''Process a CRC field of a PJON frame.'''
+
+ # CRC algorithm and width are configurable, and can differ
+ # across meta and end checksums in a frame's fields.
+ caption = 'META' if is_meta else 'END'
+ crc_len = 8 if is_meta else 32 if self.cfg_crc32 else 8
+ crc_fmt = '{:08x}' if crc_len == 32 else '{:02x}'
+ have_text = crc_fmt.format(have)
+
+ # Check received against expected checksum. Emit warnings.
+ warn_texts = []
+ data = self.frame_bytes[:-1]
+ want = calc_crc32(data) if crc_len == 32 else calc_crc8(data)
+ if want != have:
+ want_text = crc_fmt.format(want)
+ warn_texts.append('CRC mismatch - want {} have {}'.format(want_text, have_text))
+ if warn_texts:
+ warn_texts = ', '.join(warn_texts)
+ self.putg(self.ann_ss, self.ann_es, ANN_WARN, [warn_texts])
+
+ # Provide text representation for frame field, caller emits
+ # the annotation.
+ texts = [
+ '{}_CRC {}'.format(caption, have_text),
+ 'CRC {}'.format(have_text),
+ have_text,
+ ]
+ return texts
+
+ def handle_field_init_crc(self, b):
+ '''Process initial CRC (meta) field of a PJON frame.'''
+ # Caller provides a list of values. We want a single scalar.
+ b = b[0]
+ return self.handle_field_common_crc(b, True)
+
+ def handle_field_end_crc(self, b):
+ '''Process end CRC (total frame) field of a PJON frame.'''
+ # Caller provides a list of values. We want a single scalar.
+ b = b[0]
+ return self.handle_field_common_crc(b, False)
+
+ def handle_field_payload(self, b):
+ '''Process payload data field of a PJON frame.'''
+
+ self.frame_payload = b[:]
+
+ text = ' '.join(['{:02x}'.format(v) for v in b])
+ texts = [
+ 'PAYLOAD {}'.format(text),
+ text,
+ ]
+ return texts
+
+ def handle_field_sync_resp(self, b):
+ '''Process synchronous response for a PJON frame.'''
+
+ self.frame_has_ack = b
+
+ texts = [
+ 'ACK {:02x}'.format(b),
+ '{:02x}'.format(b),
+ ]
+ return texts
+
+ def decode(self, ss, es, data):
+ ptype, pdata = data
+
+ # Start frame bytes accumulation when FRAME_INIT is seen. Flush
+ # previously accumulated frame bytes when a new frame starts.
+ if ptype == 'FRAME_INIT':
+ self.frame_flush()
+ self.reset_frame()
+ self.frame_bytes = []
+ self.handle_field_seed_desc()
+ return
+
+ # Use IDLE as another (earlier) trigger to flush frames. Also
+ # trigger flushes on FRAME-DATA which mean that the link layer
+ # inspection has seen the end of a protocol frame.
+ #
+ # TODO Improve usability? Emit warnings for PJON frames where
+ # FRAME_DATA was seen but FRAME_INIT wasn't? So that users can
+ # become aware of broken frames.
+ if ptype in ('IDLE', 'FRAME_DATA'):
+ self.frame_flush()
+ self.reset_frame()
+ return
+
+ # Switch from data bytes to response bytes when WAIT is seen.
+ if ptype == 'SYNC_RESP_WAIT':
+ self.ack_bytes = []
+ self.ann_ss, self.ann_es = None, None
+ return
+
+ # Accumulate data bytes as they arrive. Put them in the bucket
+ # which corresponds to its most recently seen leader.
+ if ptype == 'DATA_BYTE':
+ b = pdata
+
+ # Are we collecting response bytes (ACK)?
+ if self.ack_bytes is not None:
+ if not self.ann_ss:
+ self.ann_ss = ss
+ self.ack_bytes.append(b)
+ self.ann_es = es
+ text = self.handle_field_sync_resp(b)
+ if text:
+ self.putg(self.ann_ss, self.ann_es, ANN_SYN_RSP, text)
+ self.ann_ss, self.ann_es = None, None
+ return
+
+ # Are we collecting frame content?
+ if self.frame_bytes is not None:
+ if not self.ann_ss:
+ self.ann_ss = ss
+ self.frame_bytes.append(b)
+ self.ann_es = es
+
+ # Has the field value become available yet?
+ desc = self.handle_field_get_desc()
+ if not desc:
+ return
+ width = desc.get('width', None)
+ if not width:
+ return
+ self.field_desc_got += 1
+ if self.field_desc_got != width:
+ return
+
+ # Grab most recent received field as a byte array. Get
+ # the values that it contains.
+ fmt = desc.get('format', '>B')
+ raw = bytearray(self.frame_bytes[-width:])
+ values = struct.unpack(fmt, raw)
+
+ # Process the value, and get its presentation. Can be
+ # mere formatting, or serious execution of logic.
+ hdl = desc.get('handler', '{!r}')
+ if isinstance(hdl, str):
+ text = [hdl.format(*values)]
+ elif isinstance(hdl, (list, tuple)):
+ text = [f.format(*values) for f in hdl]
+ elif hdl:
+ text = hdl(values)
+ cls = desc.get('anncls', ANN_ANON_DATA)
+
+ # Emit annotation unless the handler routine already did.
+ if cls is not None and text:
+ self.putg(self.ann_ss, self.ann_es, cls, text)
+ self.ann_ss, self.ann_es = None, None
+
+ # Advance scan position for to-get-received field.
+ self.field_desc_idx += 1
+ self.field_desc_got = 0
+ return
+
+ # Unknown phase, not collecting. Not synced yet to the input?
+ return
+
+ # Unknown or unhandled kind of link layer output.
+ return
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