## ## This file is part of the libsigrokdecode project. ## ## Copyright (C) 2010-2013 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 ## 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: [, ] 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) 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' 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'], ] 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_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 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 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.putp([cmd, d]) self.putx([proto[cmd][0], ['%s: %02X' % (proto[cmd][1], d), '%s: %02X' % (proto[cmd][2], d), '%02X' % 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