## ## 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. # 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: [, , ] 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) is the data or address byte associated with the 'ADDRESS*' and 'DATA*' command. For 'START', 'START REPEAT' and 'STOP', this is None. 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): api_version = 1 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.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 = 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 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 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 # 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 != 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.startsample = self.samplenum 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. super(Decoder, self).put(self.startsample, self.samplenum, output_id, data) def decode(self, ss, es, data): for samplenum, (scl, sda) in data: self.samplenum = samplenum # 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: # Shouldn't happen. raise Exception("unknown state %d" % self.STATE) # Save current SDA/SCL values for the next round. self.oldscl = scl self.oldsda = sda