## ## This file is part of the sigrok project. ## ## 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 ## 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. # # 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) # # TODO: I2C address of slaves. # TODO: Handle multiple different I2C devices on same bus # -> we need to decode multiple protocols at the same time. # # # 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': }]} # import sigrokdecode # 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'], } # export protocol keys as symbols for i2c decoders up the stack EXPORT = [ protocol.keys() ] # States FIND_START = 0 FIND_ADDRESS = 1 FIND_DATA = 2 # annotation feed formats ANN_SHIFTED = 0 ANN_SHIFTED_SHORT = 1 ANN_RAW = 2 class Decoder(sigrokdecode.Decoder): id = 'i2c' name = 'I2C' longname = 'Inter-Integrated Circuit (I2C) bus' desc = 'I2C is a two-wire, multi-master, serial bus.' longdesc = '...' author = 'Uwe Hermann' email = 'uwe@hermann-uwe.de' license = 'gplv2+' inputs = ['logic'] outputs = ['i2c'] probes = [ {'id': 'scl', 'name': 'SCL', 'desc': 'Serial clock line'}, {'id': 'sda', 'name': 'SDA', 'desc': 'Serial data line'}, ] options = { 'address-space': ['Address space (in bits)', 7], } annotation = [ # 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.output_protocol = None self.output_annotation = None 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 def start(self, metadata): self.output_protocol = self.output_new(sigrokdecode.SRD_OUTPUT_PROTOCOL, 'i2c') self.output_annotation = self.output_new(sigrokdecode.SRD_OUTPUT_ANNOTATION, '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): if self.is_repeat_start == 1: cmd = 'START_REPEAT' else: cmd = 'START' self.put(self.output_protocol, [ cmd ]) self.put(self.output_annotation, [ ANN_SHIFTED, [protocol[cmd][0]] ]) self.put(self.output_annotation, [ 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.output_annotation, [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: d = self.databyte & 0xfe # The READ/WRITE bit is only in address bytes, not data bytes. self.wr = 1 if (self.databyte & 1) else 0 elif self.state == FIND_DATA: d = self.databyte else: # TODO: Error? pass # last bit that came in was the ACK/NACK bit (1 = NACK) if sda == 1: ack_bit = 'NACK' else: ack_bit = 'ACK' # TODO: Simplify. 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.output_protocol, [ [cmd, d], [ack_bit] ] ) self.put(self.output_annotation, [ANN_SHIFTED, [ "%s" % protocol[cmd][0], "0x%02x" % d, "%s" % protocol[ack_bit][0]] ] ) self.put(self.output_annotation, [ANN_SHIFTED_SHORT, [ "%s" % protocol[cmd][1], "0x%02x" % d, "%s" % 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.output_protocol, [ 'STOP' ]) self.put(self.output_annotation, [ ANN_SHIFTED, [protocol['STOP'][0]] ]) self.put(self.output_annotation, [ 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, timeoffset, duration, 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