From: Uwe Hermann Date: Sun, 27 Nov 2011 19:17:49 +0000 (+0100) Subject: srd: i2c.py: Rework I2C decoder. X-Git-Tag: libsigrokdecode-0.1.0~262 X-Git-Url: https://sigrok.org/gitweb/?p=libsigrokdecode.git;a=commitdiff_plain;h=7b86f0bc7a0009e928e4bcc250c3e0cc12dda7ac srd: i2c.py: Rework I2C decoder. This should be working OK for most use-cases now, though there certainly are a few TODOs left. The output format is just a quick hack and will change. --- diff --git a/decoders/i2c.py b/decoders/i2c.py index f0b32e7..b99b26c 100644 --- a/decoders/i2c.py +++ b/decoders/i2c.py @@ -1,7 +1,7 @@ ## ## This file is part of the sigrok project. ## -## Copyright (C) 2010 Uwe Hermann +## Copyright (C) 2010-2011 Uwe Hermann ## ## 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 @@ -39,6 +39,7 @@ # # 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). @@ -161,13 +162,13 @@ class Decoder(): self.channels = 8 self.samplenum = 0 - self.bitcount = 0 self.databyte = 0 self.wr = -1 self.startsample = -1 - self.IDLE, self.START, self.ADDRESS, self.DATA = range(4) - self.state = self.IDLE + + self.FIND_START, self.FIND_ADDRESS, self.FIND_DATA = range(3) + self.state = self.FIND_START # Get the channel/probe number of the SCL/SDA signals. self.scl_bit = self.probes['scl']['ch'] @@ -179,10 +180,115 @@ class Decoder(): def start(self, metadata): self.unitsize = metadata["unitsize"] - 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 find_start(self, scl, sda): + out = [] + # o = {'type': 'S', 'range': (self.samplenum, self.samplenum), + # 'data': None, 'ann': None}, + o = 'S' + out.append(o) + self.state = self.FIND_ADDRESS + self.bitcount = self.databyte = 0 + self.wr = -1 + return out + + def find_address_or_data(self, scl, sda): + '''Gather 8 bits of data plus the ACK/NACK bit.''' + out = o = [] + + if self.startsample == -1: + self.startsample = self.samplenum + 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 [] + + # We received 8 address/data bits and the ACK/NACK bit. + self.databyte >>= 1 # Shift out unwanted ACK/NACK bit here. + + ack = (sda == 1) and 'N' or 'A' + + if self.state == self.FIND_ADDRESS: + d = self.databyte & 0xfe + # The READ/WRITE bit is only in address bytes, not data bytes. + self.wr = (self.databyte & 1) and 1 or 0 + elif self.state == self.FIND_DATA: + d = self.databyte + else: + # TODO: Error? + pass + + # o = {'type': self.state, + # 'range': (self.startsample, self.samplenum - 1), + # 'data': d, 'ann': None} + + o = {'data': "0x%02x" % d} + + # TODO: Simplify. + if self.state == self.FIND_ADDRESS and self.wr == 1: + o['type'] = 'AW' + elif self.state == self.FIND_ADDRESS and self.wr == 0: + o['type'] = 'AR' + elif self.state == self.FIND_DATA and self.wr == 1: + o['type'] = 'DW' + elif self.state == self.FIND_DATA and self.wr == 0: + o['type'] = 'DR' + + out.append(o) + + # o = {'type': ack, 'range': (self.samplenum, self.samplenum), + # 'data': None, 'ann': None} + o = ack + out.append(o) + self.bitcount = self.databyte = 0 + self.startsample = -1 + + if self.state == self.FIND_ADDRESS: + self.state = self.FIND_DATA + elif self.state == self.FIND_DATA: + # There could be multiple data bytes in a row. + # So, either find a STOP condition or another data byte next. + pass + + return out + + def find_stop(self, scl, sda): + out = o = [] + + # o = {'type': 'P', 'range': (self.samplenum, self.samplenum), + # 'data': None, 'ann': None}, + o = 'P' + out.append(o) + self.state = self.FIND_START + self.wr = -1 + + return out + def decode(self, data): """I2C protocol decoder""" @@ -211,73 +317,28 @@ class Decoder(): # TODO: Wait until the bus is idle (SDA = SCL = 1) first? - # START condition (S): SDA = falling, SCL = high - if (self.oldsda == 1 and sda == 0) and scl == 1: - o = {'type': 'S', 'range': (self.samplenum, self.samplenum), - 'data': None, 'ann': None}, - out.append(o) - self.state = self.ADDRESS - self.bitcount = self.databyte = 0 - - # Data latching by transmitter: SCL = low - elif (scl == 0): - pass # TODO - - # Data sampling of receiver: SCL = rising - elif (self.oldscl == 0 and scl == 1): - if self.startsample == -1: - self.startsample = self.samplenum - self.bitcount += 1 - - # out.append("%d\t\tRECEIVED BIT %d: %d\n" % \ - # (self.samplenum, 8 - bitcount, sda)) - - # Address and data are transmitted MSB-first. - self.databyte <<= 1 - self.databyte |= sda - - if self.bitcount != 9: - continue - - # We received 8 address/data bits and the ACK/NACK bit. - self.databyte >>= 1 # Shift out unwanted ACK/NACK bit here. - ack = (sda == 1) and 'N' or 'A' - d = (self.state == self.ADDRESS) and (self.databyte & 0xfe) or self.databyte - if self.state == self.ADDRESS: - self.wr = (self.databyte & 1) and 1 or 0 - self.state = self.DATA - o = {'type': self.state, - 'range': (self.startsample, self.samplenum - 1), - 'data': d, 'ann': None} - if self.state == self.ADDRESS and self.wr == 1: - o['type'] = 'AW' - elif self.state == self.ADDRESS and self.wr == 0: - o['type'] = 'AR' - elif self.state == self.DATA and self.wr == 1: - o['type'] = 'DW' - elif self.state == self.DATA and self.wr == 0: - o['type'] = 'DR' - out.append(o) - o = {'type': ack, 'range': (self.samplenum, self.samplenum), - 'data': None, 'ann': None} - out.append(o) - self.bitcount = self.databyte = self.startsample = 0 - self.startsample = -1 - - # STOP condition (P): SDA = rising, SCL = high - elif (self.oldsda == 0 and sda == 1) and scl == 1: - o = {'type': 'P', 'range': (self.samplenum, self.samplenum), - 'data': None, 'ann': None}, - out.append(o) - self.state = self.IDLE - self.wr = -1 + # State machine. + if self.state == self.FIND_START: + if self.is_start_condition(scl, sda): + out += self.find_start(scl, sda) + elif self.state == self.FIND_ADDRESS: + if self.is_data_bit(scl, sda): + out += self.find_address_or_data(scl, sda) + elif self.state == self.FIND_DATA: + if self.is_data_bit(scl, sda): + out += self.find_address_or_data(scl, sda) + elif self.is_start_condition(scl, sda): + out += self.find_start(scl, sda) + elif self.is_stop_condition(scl, sda): + out += self.find_stop(scl, sda) + else: + # TODO: Error? + pass # Save current SDA/SCL values for the next round. self.oldscl = scl self.oldsda = sda - # TODO: Which output format? - # TODO: How to only output something after the last chunk of data? if out != []: sigrok.put(out)