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##
## This file is part of the libsigrokdecode project.
##
## Copyright (C) 2010-2013 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
##
# I2C protocol decoder
# TODO: Look into arbitration, collision detection, clock synchronisation, etc.
# TODO: Implement support for 10bit slave addresses.
# TODO: Implement support for inverting SDA/SCL levels (0->1 and 1->0).
# TODO: Implement support for detecting various bus errors.
import sigrokdecode as srd
'''
Protocol output format:
I2C packet:
[<cmd>, <data>]
<cmd> is one of:
- 'START' (START condition)
- 'START REPEAT' (Repeated START condition)
- 'ADDRESS READ' (Slave address, read)
- 'ADDRESS WRITE' (Slave address, write)
- 'DATA READ' (Data, read)
- 'DATA WRITE' (Data, write)
- 'STOP' (STOP condition)
- 'ACK' (ACK bit)
- 'NACK' (NACK bit)
<data> is the data or address byte associated with the 'ADDRESS*' and 'DATA*'
command. Slave addresses do not include bit 0 (the READ/WRITE indication bit).
For example, a slave address field could be 0x51 (instead of 0xa2).
For 'START', 'START REPEAT', 'STOP', 'ACK', and 'NACK' <data> is None.
'''
# CMD: [annotation-type-index, long annotation, short annotation]
proto = {
'START': [0, 'Start', 'S'],
'START REPEAT': [1, 'Start repeat', 'Sr'],
'STOP': [2, 'Stop', 'P'],
'ACK': [3, 'ACK', 'A'],
'NACK': [4, 'NACK', 'N'],
'ADDRESS READ': [5, 'Address read', 'AR'],
'ADDRESS WRITE': [6, 'Address write', 'AW'],
'DATA READ': [7, 'Data read', 'DR'],
'DATA WRITE': [8, 'Data write', 'DW'],
}
class Decoder(srd.Decoder):
api_version = 1
id = 'i2c'
name = 'I2C'
longname = 'Inter-Integrated Circuit'
desc = 'Two-wire, multi-master, serial bus.'
license = 'gplv2+'
inputs = ['logic']
outputs = ['i2c']
probes = [
{'id': 'scl', 'name': 'SCL', 'desc': 'Serial clock line'},
{'id': 'sda', 'name': 'SDA', 'desc': 'Serial data line'},
]
optional_probes = []
options = {
'address_format': ['Displayed slave address format', 'shifted'],
}
annotations = [
['Start', 'Start condition'],
['Repeat start', 'Repeat start condition'],
['Stop', 'Stop condition'],
['ACK', 'ACK'],
['NACK', 'NACK'],
['Address read', 'Address read'],
['Address write', 'Address write'],
['Data read', 'Data read'],
['Data write', 'Data write'],
['Warnings', 'Human-readable warnings'],
]
binary = (
'Address read',
'Address write',
'Data read',
'Data write',
)
def __init__(self, **kwargs):
self.samplerate = None
self.startsample = -1
self.samplenum = None
self.bitcount = 0
self.databyte = 0
self.wr = -1
self.is_repeat_start = 0
self.state = 'FIND START'
self.oldscl = 1
self.oldsda = 1
self.oldpins = [1, 1]
self.pdu_start = None
self.pdu_bits = 0
def metadata(self, key, value):
if key == srd.SRD_CONF_SAMPLERATE:
self.samplerate = value
def start(self):
self.out_proto = self.register(srd.OUTPUT_PYTHON)
self.out_ann = self.register(srd.OUTPUT_ANN)
self.out_binary = self.add(srd.OUTPUT_BINARY)
self.out_bitrate = self.register(srd.OUTPUT_META,
meta=(int, 'Bitrate', 'Bitrate from Start bit to Stop bit'))
def putx(self, data):
self.put(self.startsample, self.samplenum, self.out_ann, data)
def putp(self, data):
self.put(self.startsample, self.samplenum, self.out_proto, data)
def putb(self, data):
self.put(self.startsample, self.samplenum, self.out_binary, data)
def is_start_condition(self, scl, sda):
# START condition (S): SDA = falling, SCL = high
if (self.oldsda == 1 and sda == 0) and scl == 1:
return True
return False
def is_data_bit(self, scl, sda):
# Data sampling of receiver: SCL = rising
if self.oldscl == 0 and scl == 1:
return True
return False
def is_stop_condition(self, scl, sda):
# STOP condition (P): SDA = rising, SCL = high
if (self.oldsda == 0 and sda == 1) and scl == 1:
return True
return False
def found_start(self, scl, sda):
self.startsample = self.samplenum
self.pdu_start = self.samplenum
self.pdu_bits = 0
cmd = 'START REPEAT' if (self.is_repeat_start == 1) else 'START'
self.putp([cmd, None])
self.putx([proto[cmd][0], proto[cmd][1:]])
self.state = 'FIND ADDRESS'
self.bitcount = self.databyte = 0
self.is_repeat_start = 1
self.wr = -1
# Gather 8 bits of data plus the ACK/NACK bit.
def found_address_or_data(self, scl, sda):
# Address and data are transmitted MSB-first.
self.databyte <<= 1
self.databyte |= sda
if self.bitcount == 0:
self.startsample = self.samplenum
# Return if we haven't collected all 8 + 1 bits, yet.
self.bitcount += 1
if self.bitcount != 8:
return
# We triggered on the ACK/NACK bit, but won't report that until later.
self.startsample -= 1
d = self.databyte
if self.state == 'FIND ADDRESS':
# The READ/WRITE bit is only in address bytes, not data bytes.
self.wr = 0 if (self.databyte & 1) else 1
if self.options['address_format'] == 'shifted':
d = d >> 1
bin_class = -1
if self.state == 'FIND ADDRESS' and self.wr == 1:
cmd = 'ADDRESS WRITE'
bin_class = 1
elif self.state == 'FIND ADDRESS' and self.wr == 0:
cmd = 'ADDRESS READ'
bin_class = 0
elif self.state == 'FIND DATA' and self.wr == 1:
cmd = 'DATA WRITE'
bin_class = 3
elif self.state == 'FIND DATA' and self.wr == 0:
cmd = 'DATA READ'
bin_class = 2
self.putp([cmd, d])
self.putx([proto[cmd][0], ['%s: %02X' % (proto[cmd][1], d),
'%s: %02X' % (proto[cmd][2], d), '%02X' % d]])
self.putb((bin_class, bytes([d])))
# Done with this packet.
self.startsample = -1
self.bitcount = self.databyte = 0
self.state = 'FIND ACK'
def get_ack(self, scl, sda):
self.startsample = self.samplenum
cmd = 'NACK' if (sda == 1) else 'ACK'
self.putp([cmd, None])
self.putx([proto[cmd][0], proto[cmd][1:]])
# There could be multiple data bytes in a row, so either find
# another data byte or a STOP condition next.
self.state = 'FIND DATA'
def found_stop(self, scl, sda):
# Meta bitrate
elapsed = 1 / float(self.samplerate) * (self.samplenum - self.pdu_start + 1)
bitrate = int(1 / elapsed * self.pdu_bits)
self.put(self.startsample, self.samplenum, self.out_bitrate, bitrate)
self.startsample = self.samplenum
cmd = 'STOP'
self.putp([cmd, None])
self.putx([proto[cmd][0], proto[cmd][1:]])
self.state = 'FIND START'
self.is_repeat_start = 0
self.wr = -1
def decode(self, ss, es, data):
if self.samplerate is None:
raise Exception("Cannot decode without samplerate.")
for (self.samplenum, pins) in data:
# Ignore identical samples early on (for performance reasons).
if self.oldpins == pins:
continue
self.oldpins, (scl, sda) = pins, pins
self.pdu_bits += 1
# TODO: Wait until the bus is idle (SDA = SCL = 1) first?
# State machine.
if self.state == 'FIND START':
if self.is_start_condition(scl, sda):
self.found_start(scl, sda)
elif self.state == 'FIND ADDRESS':
if self.is_data_bit(scl, sda):
self.found_address_or_data(scl, sda)
elif self.state == 'FIND DATA':
if self.is_data_bit(scl, sda):
self.found_address_or_data(scl, sda)
elif self.is_start_condition(scl, sda):
self.found_start(scl, sda)
elif self.is_stop_condition(scl, sda):
self.found_stop(scl, sda)
elif self.state == 'FIND ACK':
if self.is_data_bit(scl, sda):
self.get_ack(scl, sda)
else:
raise Exception('Invalid state: %s' % self.state)
# Save current SDA/SCL values for the next round.
self.oldscl = scl
self.oldsda = sda
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