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Diffstat (limited to 'decoders/i2c.py')
| -rw-r--r-- | decoders/i2c.py | 255 |
1 files changed, 255 insertions, 0 deletions
diff --git a/decoders/i2c.py b/decoders/i2c.py new file mode 100644 index 0000000..bbf6925 --- /dev/null +++ b/decoders/i2c.py @@ -0,0 +1,255 @@ +## +## This file is part of the sigrok project. +## +## Copyright (C) 2010 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 +# 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. + +# +# I2C output format: +# +# The output consists of a (Python) list of I2C "packets", each of which +# has an (implicit) index number (its index in the list). +# Each packet consists of a Python dict with certain key/value pairs. +# +# TODO: Make this a list later instead of a dict? +# +# 'type': (string) +# - 'S' (START condition) +# - 'Sr' (Repeated START) +# - 'AR' (Address, read) +# - 'AW' (Address, write) +# - 'DR' (Data, read) +# - 'DW' (Data, write) +# - 'P' (STOP condition) +# 'range': (tuple of 2 integers, the min/max samplenumber of this range) +# - (min, max) +# - min/max can also be identical. +# 'data': (actual data as integer ???) TODO: This can be very variable... +# 'ann': (string; additional annotations / comments) +# +# Example output: +# [{'type': 'S', 'range': (150, 160), 'data': None, 'ann': 'Foobar'}, +# {'type': 'AW', 'range': (200, 300), 'data': 0x50, 'ann': 'Slave 4'}, +# {'type': 'DW', 'range': (310, 370), 'data': 0x00, 'ann': 'Init cmd'}, +# {'type': 'AR', 'range': (500, 560), 'data': 0x50, 'ann': 'Get stat'}, +# {'type': 'DR', 'range': (580, 640), 'data': 0xfe, 'ann': 'OK'}, +# {'type': 'P', 'range': (650, 660), 'data': None, 'ann': None}] +# +# Possible other events: +# - Error event in case protocol looks broken: +# [{'type': 'ERROR', 'range': (min, max), +# 'data': TODO, 'ann': 'This is not a Microchip 24XX64 EEPROM'}, +# [{'type': 'ERROR', 'range': (min, max), +# 'data': TODO, 'ann': 'TODO'}, +# - TODO: Make list of possible errors accessible as metadata? +# +# TODO: I2C address of slaves. +# TODO: Handle multiple different I2C devices on same bus +# -> we need to decode multiple protocols at the same time. +# TODO: range: Always contiguous? Splitted ranges? Multiple per event? +# + +# +# I2C input format: +# +# signals: +# [[id, channel, description], ...] # TODO +# +# Example: +# {'id': 'SCL', 'ch': 5, 'desc': 'Serial clock line'} +# {'id': 'SDA', 'ch': 7, 'desc': 'Serial data line'} +# ... +# +# {'inbuf': [...], +# 'signals': [{'SCL': }]} +# + +def decode(inbuf): + """I2C protocol decoder""" + + # FIXME: Get the data in the correct format in the first place. + inbuf = [ord(x) for x in inbuf] + + # FIXME: This should be passed in as metadata, not hardcoded here. + metadata = { + 'numchannels': 8, + 'signals': { + 'scl': {'ch': 5, 'name': 'SCL', 'desc': 'Serial clock line'}, + 'sda': {'ch': 7, 'name': 'SDA', 'desc': 'Serial data line'}, + }, + } + + out = [] + o = ack = d = '' + bitcount = data = 0 + wr = startsample = -1 + IDLE, START, ADDRESS, DATA = range(4) + state = IDLE + + # Get the channel/probe number of the SCL/SDA signals. + scl_bit = metadata['signals']['scl']['ch'] + sda_bit = metadata['signals']['sda']['ch'] + + # Get SCL/SDA bit values (0/1 for low/high) of the first sample. + s = inbuf[0] + oldscl = (s & (1 << scl_bit)) >> scl_bit + oldsda = (s & (1 << sda_bit)) >> sda_bit + + # Loop over all samples. + # TODO: Handle LAs with more/less than 8 channels. + for samplenum, s in enumerate(inbuf[1:]): # We skip the first byte... + # Get SCL/SDA bit values (0/1 for low/high). + scl = (s & (1 << scl_bit)) >> scl_bit + sda = (s & (1 << sda_bit)) >> sda_bit + + # TODO: Wait until the bus is idle (SDA = SCL = 1) first? + + # START condition (S): SDA = falling, SCL = high + if (oldsda == 1 and sda == 0) and scl == 1: + o = {'type': 'S', 'range': (samplenum, samplenum), + 'data': None, 'ann': None}, + out.append(o) + state = ADDRESS + bitcount = data = 0 + + # Data latching by transmitter: SCL = low + elif (scl == 0): + pass # TODO + + # Data sampling of receiver: SCL = rising + elif (oldscl == 0 and scl == 1): + if startsample == -1: + startsample = samplenum + bitcount += 1 + + # out.append("%d\t\tRECEIVED BIT %d: %d\n" % \ + # (samplenum, 8 - bitcount, sda)) + + # Address and data are transmitted MSB-first. + data <<= 1 + data |= sda + + if bitcount != 9: + continue + + # We received 8 address/data bits and the ACK/NACK bit. + data >>= 1 # Shift out unwanted ACK/NACK bit here. + ack = (sda == 1) and 'N' or 'A' + d = (state == ADDRESS) and (data & 0xfe) or data + if state == ADDRESS: + wr = (data & 1) and 1 or 0 + state = DATA + o = {'type': state, + 'range': (startsample, samplenum - 1), + 'data': d, 'ann': None} + if state == ADDRESS and wr == 1: + o['type'] = 'AW' + elif state == ADDRESS and wr == 0: + o['type'] = 'AR' + elif state == DATA and wr == 1: + o['type'] = 'DW' + elif state == DATA and wr == 0: + o['type'] = 'DR' + out.append(o) + o = {'type': ack, 'range': (samplenum, samplenum), + 'data': None, 'ann': None} + out.append(o) + bitcount = data = startsample = 0 + startsample = -1 + + # STOP condition (P): SDA = rising, SCL = high + elif (oldsda == 0 and sda == 1) and scl == 1: + o = {'type': 'P', 'range': (samplenum, samplenum), + 'data': None, 'ann': None}, + out.append(o) + state = IDLE + wr = -1 + + # Save current SDA/SCL values for the next round. + oldscl = scl + oldsda = sda + + # FIXME: Just for testing... + return str(out) + +def register(): + return { + 'id': 'i2c', + 'name': 'I2C', + 'desc': 'Inter-Integrated Circuit (I2C) bus', + 'inputformats': ['raw'], + 'signalnames': { + 'SCL': 'Serial clock line', + 'SDA': 'Serial data line', + }, + 'outputformats': ['i2c'], + } + +# Use psyco (if available) as it results in huge performance improvements. +try: + import psyco + psyco.bind(decode) +except ImportError: + pass + |