[libsigrokdecode.git] / decoders / uart / uart.py

##
## This file is part of the sigrok project.
##
## Copyright (C) 2011-2012 Uwe Hermann <uwe@hermann-uwe.de>
##
## 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, write to the Free Software
## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
##

#
# UART protocol decoder
#

import sigrokdecode as srd

# States
WAIT_FOR_START_BIT = 0
GET_START_BIT = 1
GET_DATA_BITS = 2
GET_PARITY_BIT = 3
GET_STOP_BITS = 4

# Used for differentiating between the two data directions.
RX = 0
TX = 1

# Annotation feed formats
ANN_ASCII = 0
ANN_DEC = 1
ANN_HEX = 2
ANN_OCT = 3
ANN_BITS = 4

# Given a parity type to check (odd, even, zero, one), the value of the
# parity bit, the value of the data, and the length of the data (5-9 bits,
# usually 8 bits) return True if the parity is correct, False otherwise.
# 'none' is _not_ allowed as value for 'parity_type'.
def parity_ok(parity_type, parity_bit, data, num_data_bits):

    # Handle easy cases first (parity bit is always 1 or 0).
    if parity_type == 'zero':
        return parity_bit == 0
    elif parity_type == 'one':
        return parity_bit == 1

    # Count number of 1 (high) bits in the data (and the parity bit itself!).
    ones = bin(data).count('1') + parity_bit

    # Check for odd/even parity.
    if parity_type == 'odd':
        return (ones % 2) == 1
    elif parity_type == 'even':
        return (ones % 2) == 0
    else:
        raise Exception('Invalid parity type: %d' % parity_type)

class Decoder(srd.Decoder):
    api_version = 1
    id = 'uart'
    name = 'UART'
    longname = 'Universal Asynchronous Receiver/Transmitter'
    desc = 'Universal Asynchronous Receiver/Transmitter (UART)'
    longdesc = 'TODO.'
    license = 'gplv2+'
    inputs = ['logic']
    outputs = ['uart']
    probes = [
        # Allow specifying only one of the signals, e.g. if only one data
        # direction exists (or is relevant).
        {'id': 'rx', 'name': 'RX', 'desc': 'UART receive line'},
        {'id': 'tx', 'name': 'TX', 'desc': 'UART transmit line'},
    ]
    optional_probes = []
    options = {
        'baudrate': ['Baud rate', 115200],
        'num_data_bits': ['Data bits', 8], # Valid: 5-9.
        'parity_type': ['Parity type', 'none'],
        'parity_check': ['Check parity?', 'yes'], # TODO: Bool supported?
        'num_stop_bits': ['Stop bit(s)', '1'], # String! 0, 0.5, 1, 1.5.
        'bit_order': ['Bit order', 'lsb-first'],
        # TODO: Options to invert the signal(s).
    }
    annotations = [
        ['ASCII', 'Data bytes as ASCII characters'],
        ['Decimal', 'Databytes as decimal, integer values'],
        ['Hex', 'Data bytes in hex format'],
        ['Octal', 'Data bytes as octal numbers'],
        ['Bits', 'Data bytes in bit notation (sequence of 0/1 digits)'],
    ]

    def putx(self, rxtx, data):
        self.put(self.startsample[rxtx], self.samplenum - 1, self.out_ann, data)

    def __init__(self, **kwargs):
        self.samplenum = 0
        self.frame_start = [-1, -1]
        self.startbit = [-1, -1]
        self.cur_data_bit = [0, 0]
        self.databyte = [0, 0]
        self.paritybit = [-1, -1]
        self.stopbit1 = [-1, -1]
        self.startsample = [-1, -1]

        # Initial state.
        self.state = [WAIT_FOR_START_BIT, WAIT_FOR_START_BIT]

        self.oldbit = [None, None]

    def start(self, metadata):
        self.samplerate = metadata['samplerate']
        self.out_proto = self.add(srd.OUTPUT_PROTO, 'uart')
        self.out_ann = self.add(srd.OUTPUT_ANN, 'uart')

        # The width of one UART bit in number of samples.
        self.bit_width = \
            float(self.samplerate) / float(self.options['baudrate'])

    def report(self):
        pass

    # Return true if we reached the middle of the desired bit, false otherwise.
    def reached_bit(self, rxtx, bitnum):
        # bitpos is the samplenumber which is in the middle of the
        # specified UART bit (0 = start bit, 1..x = data, x+1 = parity bit
        # (if used) or the first stop bit, and so on).
        bitpos = self.frame_start[rxtx] + (self.bit_width / 2.0)
        bitpos += bitnum * self.bit_width
        if self.samplenum >= bitpos:
            return True
        return False

    def reached_bit_last(self, rxtx, bitnum):
        bitpos = self.frame_start[rxtx] + ((bitnum + 1) * self.bit_width)
        if self.samplenum >= bitpos:
            return True
        return False

    def wait_for_start_bit(self, rxtx, old_signal, signal):
        # The start bit is always 0 (low). As the idle UART (and the stop bit)
        # level is 1 (high), the beginning of a start bit is a falling edge.
        if not (old_signal == 1 and signal == 0):
            return

        # Save the sample number where the start bit begins.
        self.frame_start[rxtx] = self.samplenum

        self.state[rxtx] = GET_START_BIT

    def get_start_bit(self, rxtx, signal):
        # Skip samples until we're in the middle of the start bit.
        if not self.reached_bit(rxtx, 0):
            return

        self.startbit[rxtx] = signal

        # The startbit must be 0. If not, we report an error.
        if self.startbit[rxtx] != 0:
            self.put(self.frame_start[rxtx], self.samplenum, self.out_proto,
                     ['INVALID STARTBIT', rxtx, self.startbit[rxtx]])
            # TODO: Abort? Ignore rest of the frame?

        self.cur_data_bit[rxtx] = 0
        self.databyte[rxtx] = 0
        self.startsample[rxtx] = -1

        self.state[rxtx] = GET_DATA_BITS

        self.put(self.frame_start[rxtx], self.samplenum, self.out_proto,
                 ['STARTBIT', rxtx, self.startbit[rxtx]])
        self.put(self.frame_start[rxtx], self.samplenum, self.out_ann,
                 [ANN_ASCII, ['Start bit', 'Start', 'S']])

    def get_data_bits(self, rxtx, signal):
        # Skip samples until we're in the middle of the desired data bit.
        if not self.reached_bit(rxtx, self.cur_data_bit[rxtx] + 1):
            return

        # Save the sample number where the data byte starts.
        if self.startsample[rxtx] == -1:
            self.startsample[rxtx] = self.samplenum

        # Get the next data bit in LSB-first or MSB-first fashion.
        if self.options['bit_order'] == 'lsb-first':
            self.databyte[rxtx] >>= 1
            self.databyte[rxtx] |= \
                (signal << (self.options['num_data_bits'] - 1))
        elif self.options['bit_order'] == 'msb-first':
            self.databyte[rxtx] <<= 1
            self.databyte[rxtx] |= (signal << 0)
        else:
            raise Exception('Invalid bit order value: %s',
                            self.options['bit_order'])

        # Return here, unless we already received all data bits.
        # TODO? Off-by-one?
        if self.cur_data_bit[rxtx] < self.options['num_data_bits'] - 1:
            self.cur_data_bit[rxtx] += 1
            return

        self.state[rxtx] = GET_PARITY_BIT

        self.put(self.startsample[rxtx], self.samplenum - 1, self.out_proto,
                 ['DATA', rxtx, self.databyte[rxtx]])

        s = 'RX: ' if (rxtx == RX) else 'TX: '
        self.putx(rxtx, [ANN_ASCII, [s + chr(self.databyte[rxtx])]])
        self.putx(rxtx, [ANN_DEC,   [s + str(self.databyte[rxtx])]])
        self.putx(rxtx, [ANN_HEX,   [s + hex(self.databyte[rxtx]),
                                     s + hex(self.databyte[rxtx])[2:]]])
        self.putx(rxtx, [ANN_OCT,   [s + oct(self.databyte[rxtx]),
                                     s + oct(self.databyte[rxtx])[2:]]])
        self.putx(rxtx, [ANN_BITS,  [s + bin(self.databyte[rxtx]),
                                     s + bin(self.databyte[rxtx])[2:]]])

    def get_parity_bit(self, rxtx, signal):
        # If no parity is used/configured, skip to the next state immediately.
        if self.options['parity_type'] == 'none':
            self.state[rxtx] = GET_STOP_BITS
            return

        # Skip samples until we're in the middle of the parity bit.
        if not self.reached_bit(rxtx, self.options['num_data_bits'] + 1):
            return

        self.paritybit[rxtx] = signal

        self.state[rxtx] = GET_STOP_BITS

        if parity_ok(self.options['parity_type'], self.paritybit[rxtx],
                     self.databyte[rxtx], self.options['num_data_bits']):
            # TODO: Fix range.
            self.put(self.samplenum, self.samplenum, self.out_proto,
                     ['PARITYBIT', rxtx, self.paritybit[rxtx]])
            self.put(self.samplenum, self.samplenum, self.out_ann,
                     [ANN_ASCII, ['Parity bit', 'Parity', 'P']])
        else:
            # TODO: Fix range.
            # TODO: Return expected/actual parity values.
            self.put(self.samplenum, self.samplenum, self.out_proto,
                     ['PARITY ERROR', rxtx, (0, 1)]) # FIXME: Dummy tuple...
            self.put(self.samplenum, self.samplenum, self.out_ann,
                     [ANN_ASCII, ['Parity error', 'Parity err', 'PE']])

    # TODO: Currently only supports 1 stop bit.
    def get_stop_bits(self, rxtx, signal):
        # Skip samples until we're in the middle of the stop bit(s).
        skip_parity = 0 if self.options['parity_type'] == 'none' else 1
        b = self.options['num_data_bits'] + 1 + skip_parity
        if not self.reached_bit(rxtx, b):
            return

        self.stopbit1[rxtx] = signal

        # Stop bits must be 1. If not, we report an error.
        if self.stopbit1[rxtx] != 1:
            self.put(self.frame_start[rxtx], self.samplenum, self.out_proto,
                     ['INVALID STOPBIT', rxtx, self.stopbit1[rxtx]])
            # TODO: Abort? Ignore the frame? Other?

        self.state[rxtx] = WAIT_FOR_START_BIT

        # TODO: Fix range.
        self.put(self.samplenum, self.samplenum, self.out_proto,
                 ['STOPBIT', rxtx, self.stopbit1[rxtx]])
        self.put(self.samplenum, self.samplenum, self.out_ann,
                 [ANN_ASCII, ['Stop bit', 'Stop', 'P']])

    def decode(self, ss, es, data):
        # TODO: Either RX or TX could be omitted (optional probe).
        for (samplenum, (rx, tx)) in data:

            # TODO: Start counting at 0 or 1? Increase before or after?
            self.samplenum += 1

            # First sample: Save RX/TX value.
            if self.oldbit[RX] == None:
                self.oldbit[RX] = rx
                continue
            if self.oldbit[TX] == None:
                self.oldbit[TX] = tx
                continue

            # State machine.
            for rxtx in (RX, TX):
                signal = rx if (rxtx == RX) else tx

                if self.state[rxtx] == WAIT_FOR_START_BIT:
                    self.wait_for_start_bit(rxtx, self.oldbit[rxtx], signal)
                elif self.state[rxtx] == GET_START_BIT:
                    self.get_start_bit(rxtx, signal)
                elif self.state[rxtx] == GET_DATA_BITS:
                    self.get_data_bits(rxtx, signal)
                elif self.state[rxtx] == GET_PARITY_BIT:
                    self.get_parity_bit(rxtx, signal)
                elif self.state[rxtx] == GET_STOP_BITS:
                    self.get_stop_bits(rxtx, signal)
                else:
                    raise Exception('Invalid state: %d' % self.state[rxtx])

                # Save current RX/TX values for the next round.
                self.oldbit[rxtx] = signal
Commit	Line	Data
	1	##
	2	## This file is part of the sigrok project.
	3	##
	4	## Copyright (C) 2011-2012 Uwe Hermann <uwe@hermann-uwe.de>
	5	##
	6	## This program is free software; you can redistribute it and/or modify
	7	## it under the terms of the GNU General Public License as published by
	8	## the Free Software Foundation; either version 2 of the License, or
	9	## (at your option) any later version.
	10	##
	11	## This program is distributed in the hope that it will be useful,
	12	## but WITHOUT ANY WARRANTY; without even the implied warranty of
	13	## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	14	## GNU General Public License for more details.
	15	##
	16	## You should have received a copy of the GNU General Public License
	17	## along with this program; if not, write to the Free Software
	18	## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
	19	##
	20
	21	#
	22	# UART protocol decoder
	23	#
	24
	25	import sigrokdecode as srd
	26
	27	# States
	28	WAIT_FOR_START_BIT = 0
	29	GET_START_BIT = 1
	30	GET_DATA_BITS = 2
	31	GET_PARITY_BIT = 3
	32	GET_STOP_BITS = 4
	33
	34	# Used for differentiating between the two data directions.
	35	RX = 0
	36	TX = 1
	37
	38	# Annotation feed formats
	39	ANN_ASCII = 0
	40	ANN_DEC = 1
	41	ANN_HEX = 2
	42	ANN_OCT = 3
	43	ANN_BITS = 4
	44
	45	# Given a parity type to check (odd, even, zero, one), the value of the
	46	# parity bit, the value of the data, and the length of the data (5-9 bits,
	47	# usually 8 bits) return True if the parity is correct, False otherwise.
	48	# 'none' is _not_ allowed as value for 'parity_type'.
	49	def parity_ok(parity_type, parity_bit, data, num_data_bits):
	50
	51	# Handle easy cases first (parity bit is always 1 or 0).
	52	if parity_type == 'zero':
	53	return parity_bit == 0
	54	elif parity_type == 'one':
	55	return parity_bit == 1
	56
	57	# Count number of 1 (high) bits in the data (and the parity bit itself!).
	58	ones = bin(data).count('1') + parity_bit
	59
	60	# Check for odd/even parity.
	61	if parity_type == 'odd':
	62	return (ones % 2) == 1
	63	elif parity_type == 'even':
	64	return (ones % 2) == 0
	65	else:
	66	raise Exception('Invalid parity type: %d' % parity_type)
	67
	68	class Decoder(srd.Decoder):
	69	api_version = 1
	70	id = 'uart'
	71	name = 'UART'
	72	longname = 'Universal Asynchronous Receiver/Transmitter'
	73	desc = 'Universal Asynchronous Receiver/Transmitter (UART)'
	74	longdesc = 'TODO.'
	75	license = 'gplv2+'
	76	inputs = ['logic']
	77	outputs = ['uart']
	78	probes = [
	79	# Allow specifying only one of the signals, e.g. if only one data
	80	# direction exists (or is relevant).
	81	{'id': 'rx', 'name': 'RX', 'desc': 'UART receive line'},
	82	{'id': 'tx', 'name': 'TX', 'desc': 'UART transmit line'},
	83	]
	84	optional_probes = []
	85	options = {
	86	'baudrate': ['Baud rate', 115200],
	87	'num_data_bits': ['Data bits', 8], # Valid: 5-9.
	88	'parity_type': ['Parity type', 'none'],
	89	'parity_check': ['Check parity?', 'yes'], # TODO: Bool supported?
	90	'num_stop_bits': ['Stop bit(s)', '1'], # String! 0, 0.5, 1, 1.5.
	91	'bit_order': ['Bit order', 'lsb-first'],
	92	# TODO: Options to invert the signal(s).
	93	}
	94	annotations = [
	95	['ASCII', 'Data bytes as ASCII characters'],
	96	['Decimal', 'Databytes as decimal, integer values'],
	97	['Hex', 'Data bytes in hex format'],
	98	['Octal', 'Data bytes as octal numbers'],
	99	['Bits', 'Data bytes in bit notation (sequence of 0/1 digits)'],
	100	]
	101
	102	def putx(self, rxtx, data):
	103	self.put(self.startsample[rxtx], self.samplenum - 1, self.out_ann, data)
	104
	105	def __init__(self, **kwargs):
	106	self.samplenum = 0
	107	self.frame_start = [-1, -1]
	108	self.startbit = [-1, -1]
	109	self.cur_data_bit = [0, 0]
	110	self.databyte = [0, 0]
	111	self.paritybit = [-1, -1]
	112	self.stopbit1 = [-1, -1]
	113	self.startsample = [-1, -1]
	114
	115	# Initial state.
	116	self.state = [WAIT_FOR_START_BIT, WAIT_FOR_START_BIT]
	117
	118	self.oldbit = [None, None]
	119
	120	def start(self, metadata):
	121	self.samplerate = metadata['samplerate']
	122	self.out_proto = self.add(srd.OUTPUT_PROTO, 'uart')
	123	self.out_ann = self.add(srd.OUTPUT_ANN, 'uart')
	124
	125	# The width of one UART bit in number of samples.
	126	self.bit_width = \
	127	float(self.samplerate) / float(self.options['baudrate'])
	128
	129	def report(self):
	130	pass
	131
	132	# Return true if we reached the middle of the desired bit, false otherwise.
	133	def reached_bit(self, rxtx, bitnum):
	134	# bitpos is the samplenumber which is in the middle of the
	135	# specified UART bit (0 = start bit, 1..x = data, x+1 = parity bit
	136	# (if used) or the first stop bit, and so on).
	137	bitpos = self.frame_start[rxtx] + (self.bit_width / 2.0)
	138	bitpos += bitnum * self.bit_width
	139	if self.samplenum >= bitpos:
	140	return True
	141	return False
	142
	143	def reached_bit_last(self, rxtx, bitnum):
	144	bitpos = self.frame_start[rxtx] + ((bitnum + 1) * self.bit_width)
	145	if self.samplenum >= bitpos:
	146	return True
	147	return False
	148
	149	def wait_for_start_bit(self, rxtx, old_signal, signal):
	150	# The start bit is always 0 (low). As the idle UART (and the stop bit)
	151	# level is 1 (high), the beginning of a start bit is a falling edge.
	152	if not (old_signal == 1 and signal == 0):
	153	return
	154
	155	# Save the sample number where the start bit begins.
	156	self.frame_start[rxtx] = self.samplenum
	157
	158	self.state[rxtx] = GET_START_BIT
	159
	160	def get_start_bit(self, rxtx, signal):
	161	# Skip samples until we're in the middle of the start bit.
	162	if not self.reached_bit(rxtx, 0):
	163	return
	164
	165	self.startbit[rxtx] = signal
	166
	167	# The startbit must be 0. If not, we report an error.
	168	if self.startbit[rxtx] != 0:
	169	self.put(self.frame_start[rxtx], self.samplenum, self.out_proto,
	170	['INVALID STARTBIT', rxtx, self.startbit[rxtx]])
	171	# TODO: Abort? Ignore rest of the frame?
	172
	173	self.cur_data_bit[rxtx] = 0
	174	self.databyte[rxtx] = 0
	175	self.startsample[rxtx] = -1
	176
	177	self.state[rxtx] = GET_DATA_BITS
	178
	179	self.put(self.frame_start[rxtx], self.samplenum, self.out_proto,
	180	['STARTBIT', rxtx, self.startbit[rxtx]])
	181	self.put(self.frame_start[rxtx], self.samplenum, self.out_ann,
	182	[ANN_ASCII, ['Start bit', 'Start', 'S']])
	183
	184	def get_data_bits(self, rxtx, signal):
	185	# Skip samples until we're in the middle of the desired data bit.
	186	if not self.reached_bit(rxtx, self.cur_data_bit[rxtx] + 1):
	187	return
	188
	189	# Save the sample number where the data byte starts.
	190	if self.startsample[rxtx] == -1:
	191	self.startsample[rxtx] = self.samplenum
	192
	193	# Get the next data bit in LSB-first or MSB-first fashion.
	194	if self.options['bit_order'] == 'lsb-first':
	195	self.databyte[rxtx] >>= 1
	196	self.databyte[rxtx] \|= \
	197	(signal << (self.options['num_data_bits'] - 1))
	198	elif self.options['bit_order'] == 'msb-first':
	199	self.databyte[rxtx] <<= 1
	200	self.databyte[rxtx] \|= (signal << 0)
	201	else:
	202	raise Exception('Invalid bit order value: %s',
	203	self.options['bit_order'])
	204
	205	# Return here, unless we already received all data bits.
	206	# TODO? Off-by-one?
	207	if self.cur_data_bit[rxtx] < self.options['num_data_bits'] - 1:
	208	self.cur_data_bit[rxtx] += 1
	209	return
	210
	211	self.state[rxtx] = GET_PARITY_BIT
	212
	213	self.put(self.startsample[rxtx], self.samplenum - 1, self.out_proto,
	214	['DATA', rxtx, self.databyte[rxtx]])
	215
	216	s = 'RX: ' if (rxtx == RX) else 'TX: '
	217	self.putx(rxtx, [ANN_ASCII, [s + chr(self.databyte[rxtx])]])
	218	self.putx(rxtx, [ANN_DEC, [s + str(self.databyte[rxtx])]])
	219	self.putx(rxtx, [ANN_HEX, [s + hex(self.databyte[rxtx]),
	220	s + hex(self.databyte[rxtx])[2:]]])
	221	self.putx(rxtx, [ANN_OCT, [s + oct(self.databyte[rxtx]),
	222	s + oct(self.databyte[rxtx])[2:]]])
	223	self.putx(rxtx, [ANN_BITS, [s + bin(self.databyte[rxtx]),
	224	s + bin(self.databyte[rxtx])[2:]]])
	225
	226	def get_parity_bit(self, rxtx, signal):
	227	# If no parity is used/configured, skip to the next state immediately.
	228	if self.options['parity_type'] == 'none':
	229	self.state[rxtx] = GET_STOP_BITS
	230	return
	231
	232	# Skip samples until we're in the middle of the parity bit.
	233	if not self.reached_bit(rxtx, self.options['num_data_bits'] + 1):
	234	return
	235
	236	self.paritybit[rxtx] = signal
	237
	238	self.state[rxtx] = GET_STOP_BITS
	239
	240	if parity_ok(self.options['parity_type'], self.paritybit[rxtx],
	241	self.databyte[rxtx], self.options['num_data_bits']):
	242	# TODO: Fix range.
	243	self.put(self.samplenum, self.samplenum, self.out_proto,
	244	['PARITYBIT', rxtx, self.paritybit[rxtx]])
	245	self.put(self.samplenum, self.samplenum, self.out_ann,
	246	[ANN_ASCII, ['Parity bit', 'Parity', 'P']])
	247	else:
	248	# TODO: Fix range.
	249	# TODO: Return expected/actual parity values.
	250	self.put(self.samplenum, self.samplenum, self.out_proto,
	251	['PARITY ERROR', rxtx, (0, 1)]) # FIXME: Dummy tuple...
	252	self.put(self.samplenum, self.samplenum, self.out_ann,
	253	[ANN_ASCII, ['Parity error', 'Parity err', 'PE']])
	254
	255	# TODO: Currently only supports 1 stop bit.
	256	def get_stop_bits(self, rxtx, signal):
	257	# Skip samples until we're in the middle of the stop bit(s).
	258	skip_parity = 0 if self.options['parity_type'] == 'none' else 1
	259	b = self.options['num_data_bits'] + 1 + skip_parity
	260	if not self.reached_bit(rxtx, b):
	261	return
	262
	263	self.stopbit1[rxtx] = signal
	264
	265	# Stop bits must be 1. If not, we report an error.
	266	if self.stopbit1[rxtx] != 1:
	267	self.put(self.frame_start[rxtx], self.samplenum, self.out_proto,
	268	['INVALID STOPBIT', rxtx, self.stopbit1[rxtx]])
	269	# TODO: Abort? Ignore the frame? Other?
	270
	271	self.state[rxtx] = WAIT_FOR_START_BIT
	272
	273	# TODO: Fix range.
	274	self.put(self.samplenum, self.samplenum, self.out_proto,
	275	['STOPBIT', rxtx, self.stopbit1[rxtx]])
	276	self.put(self.samplenum, self.samplenum, self.out_ann,
	277	[ANN_ASCII, ['Stop bit', 'Stop', 'P']])
	278
	279	def decode(self, ss, es, data):
	280	# TODO: Either RX or TX could be omitted (optional probe).
	281	for (samplenum, (rx, tx)) in data:
	282
	283	# TODO: Start counting at 0 or 1? Increase before or after?
	284	self.samplenum += 1
	285
	286	# First sample: Save RX/TX value.
	287	if self.oldbit[RX] == None:
	288	self.oldbit[RX] = rx
	289	continue
	290	if self.oldbit[TX] == None:
	291	self.oldbit[TX] = tx
	292	continue
	293
	294	# State machine.
	295	for rxtx in (RX, TX):
	296	signal = rx if (rxtx == RX) else tx
	297
	298	if self.state[rxtx] == WAIT_FOR_START_BIT:
	299	self.wait_for_start_bit(rxtx, self.oldbit[rxtx], signal)
	300	elif self.state[rxtx] == GET_START_BIT:
	301	self.get_start_bit(rxtx, signal)
	302	elif self.state[rxtx] == GET_DATA_BITS:
	303	self.get_data_bits(rxtx, signal)
	304	elif self.state[rxtx] == GET_PARITY_BIT:
	305	self.get_parity_bit(rxtx, signal)
	306	elif self.state[rxtx] == GET_STOP_BITS:
	307	self.get_stop_bits(rxtx, signal)
	308	else:
	309	raise Exception('Invalid state: %d' % self.state[rxtx])
	310
	311	# Save current RX/TX values for the next round.
	312	self.oldbit[rxtx] = signal
	313