##
## This file is part of the sigrok project.
##
## Copyright (C) 2010-2011 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
#
#
# The Inter-Integrated Circuit (I2C) bus is a bidirectional, multi-master
# bus using two signals (SCL = serial clock line, SDA = serial data line).
#
# There can be many devices on the same bus. Each device can potentially be
# master or slave (and that can change during runtime). Both slave and master
# can potentially play the transmitter or receiver role (this can also
# change at runtime).
#
# Possible maximum data rates:
# - Standard mode: 100 kbit/s
# - Fast mode: 400 kbit/s
# - Fast-mode Plus: 1 Mbit/s
# - High-speed mode: 3.4 Mbit/s
#
# START condition (S): SDA = falling, SCL = high
# Repeated START condition (Sr): same as S
# Data bit sampling: SCL = rising
# STOP condition (P): SDA = rising, SCL = high
#
# All data bytes on SDA are exactly 8 bits long (transmitted MSB-first).
# Each byte has to be followed by a 9th ACK/NACK bit. If that bit is low,
# that indicates an ACK, if it's high that indicates a NACK.
#
# After the first START condition, a master sends the device address of the
# slave it wants to talk to. Slave addresses are 7 bits long (MSB-first).
# After those 7 bits, a data direction bit is sent. If the bit is low that
# indicates a WRITE operation, if it's high that indicates a READ operation.
#
# Later an optional 10bit slave addressing scheme was added.
#
# Documentation:
# http://www.nxp.com/acrobat/literature/9398/39340011.pdf (v2.1 spec)
# http://www.nxp.com/acrobat/usermanuals/UM10204_3.pdf (v3 spec)
# http://en.wikipedia.org/wiki/I2C
#
# TODO: Look into arbitration, collision detection, clock synchronisation, etc.
# TODO: Handle clock stretching.
# TODO: Handle combined messages / repeated START.
# TODO: Implement support for 7bit and 10bit slave addresses.
# TODO: Implement support for inverting SDA/SCL levels (0->1 and 1->0).
# TODO: Implement support for detecting various bus errors.
# TODO: I2C address of slaves.
# TODO: Handle multiple different I2C devices on same bus
# -> we need to decode multiple protocols at the same time.
'''
Protocol output format:
I2C packet:
[<i2c_command>, <data>, <ack_bit>]
<i2c_command> is one of:
- 'START' (START condition)
- 'START REPEAT' (Repeated START)
- 'ADDRESS READ' (Address, read)
- 'ADDRESS WRITE' (Address, write)
- 'DATA READ' (Data, read)
- 'DATA WRITE' (Data, write)
- 'STOP' (STOP condition)
<data> is the data or address byte associated with the 'ADDRESS*' and 'DATA*'
command. For 'START', 'START REPEAT' and 'STOP', this is None.
<ack_bit> is either 'ACK' or 'NACK', but may also be None.
'''
import sigrokdecode as srd
# Annotation feed formats
ANN_SHIFTED = 0
ANN_SHIFTED_SHORT = 1
ANN_RAW = 2
# Values are verbose and short annotation, respectively.
protocol = {
'START': ['START', 'S'],
'START REPEAT': ['START REPEAT', 'Sr'],
'STOP': ['STOP', 'P'],
'ACK': ['ACK', 'A'],
'NACK': ['NACK', 'N'],
'ADDRESS READ': ['ADDRESS READ', 'AR'],
'ADDRESS WRITE': ['ADDRESS WRITE', 'AW'],
'DATA READ': ['DATA READ', 'DR'],
'DATA WRITE': ['DATA WRITE', 'DW'],
}
# States
FIND_START = 0
FIND_ADDRESS = 1
FIND_DATA = 2
class Decoder(srd.Decoder):
id = 'i2c'
name = 'I2C'
longname = 'Inter-Integrated Circuit'
desc = 'I2C is a two-wire, multi-master, serial bus.'
longdesc = '...'
license = 'gplv2+'
inputs = ['logic']
outputs = ['i2c']
probes = [
{'id': 'scl', 'name': 'SCL', 'desc': 'Serial clock line'},
{'id': 'sda', 'name': 'SDA', 'desc': 'Serial data line'},
]
options = {
'addressing': ['Slave addressing (in bits)', 7], # 7 or 10
}
annotations = [
# ANN_SHIFTED
['7-bit shifted hex',
'Read/write bit shifted out from the 8-bit I2C slave address'],
# ANN_SHIFTED_SHORT
['7-bit shifted hex (short)',
'Read/write bit shifted out from the 8-bit I2C slave address'],
# ANN_RAW
['Raw hex', 'Unaltered raw data'],
]
def __init__(self, **kwargs):
self.samplecnt = 0
self.bitcount = 0
self.databyte = 0
self.wr = -1
self.startsample = -1
self.is_repeat_start = 0
self.state = FIND_START
self.oldscl = None
self.oldsda = None
# Set protocol decoder option defaults.
self.addressing = Decoder.options['addressing'][1]
def start(self, metadata):
self.out_proto = self.add(srd.OUTPUT_PROTO, 'i2c')
self.out_ann = self.add(srd.OUTPUT_ANN, 'i2c')
def report(self):
pass
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):
cmd = 'START REPEAT' if (self.is_repeat_start == 1) else 'START'
self.put(self.out_proto, [cmd, None, None])
self.put(self.out_ann, [ANN_SHIFTED, [protocol[cmd][0]]])
self.put(self.out_ann, [ANN_SHIFTED_SHORT, [protocol[cmd][1]]])
self.state = FIND_ADDRESS
self.bitcount = self.databyte = 0
self.is_repeat_start = 1
self.wr = -1
def found_address_or_data(self, scl, sda):
# Gather 8 bits of data plus the ACK/NACK bit.
if self.startsample == -1:
# TODO: Should be samplenum, as received from the feed.
self.startsample = self.samplecnt
self.bitcount += 1
# Address and data are transmitted MSB-first.
self.databyte <<= 1
self.databyte |= sda
# Return if we haven't collected all 8 + 1 bits, yet.
if self.bitcount != 9:
return
# Send raw output annotation before we start shifting out
# read/write and ack/nack bits.
self.put(self.out_ann, [ANN_RAW, ['0x%.2x' % self.databyte]])
# We received 8 address/data bits and the ACK/NACK bit.
self.databyte >>= 1 # Shift out unwanted ACK/NACK bit here.
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
d = self.databyte >> 1
elif self.state == FIND_DATA:
d = self.databyte
else:
# TODO: Error?
pass
# Last bit that came in was the ACK/NACK bit (1 = NACK).
ack_bit = 'NACK' if (sda == 1) else 'ACK'
if self.state == FIND_ADDRESS and self.wr == 1:
cmd = 'ADDRESS WRITE'
elif self.state == FIND_ADDRESS and self.wr == 0:
cmd = 'ADDRESS READ'
elif self.state == FIND_DATA and self.wr == 1:
cmd = 'DATA WRITE'
elif self.state == FIND_DATA and self.wr == 0:
cmd = 'DATA READ'
self.put(self.out_proto, [cmd, d, ack_bit])
self.put(self.out_ann, [ANN_SHIFTED,
[protocol[cmd][0], '0x%02x' % d, protocol[ack_bit][0]]])
self.put(self.out_ann, [ANN_SHIFTED_SHORT,
[protocol[cmd][1], '0x%02x' % d, protocol[ack_bit][1]]])
self.bitcount = self.databyte = 0
self.startsample = -1
if self.state == FIND_ADDRESS:
self.state = FIND_DATA
elif self.state == FIND_DATA:
# There could be multiple data bytes in a row.
# So, either find a STOP condition or another data byte next.
pass
def found_stop(self, scl, sda):
self.put(self.out_proto, ['STOP', None, None])
self.put(self.out_ann, [ANN_SHIFTED, [protocol['STOP'][0]]])
self.put(self.out_ann, [ANN_SHIFTED_SHORT, [protocol['STOP'][1]]])
self.state = FIND_START
self.is_repeat_start = 0
self.wr = -1
def put(self, output_id, data):
# Inject sample range into the call up to sigrok.
# TODO: 0-0 sample range for now.
super(Decoder, self).put(0, 0, output_id, data)
def decode(self, ss, es, data):
for samplenum, (scl, sda) in data:
self.samplecnt += 1
# First sample: Save SCL/SDA value.
if self.oldscl == None:
self.oldscl = scl
self.oldsda = sda
continue
# 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)
else:
# TODO: Error?
pass
# Save current SDA/SCL values for the next round.
self.oldscl = scl
self.oldsda = sda