spi: Don't decode data lines if CS isn't asserted

[libsigrokdecode.git] / decoders / spi / pd.py

##
## This file is part of the libsigrokdecode project.
##
## Copyright (C) 2011 Gareth McMullin <gareth@blacksphere.co.nz>
## Copyright (C) 2012-2014 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
##

import sigrokdecode as srd

'''
OUTPUT_PYTHON format:

Packet:
[<ptype>, <data1>, <data2>]

<ptype>:
 - 'DATA': <data1> contains the MOSI data, <data2> contains the MISO data.
   The data is _usually_ 8 bits (but can also be fewer or more bits).
   Both data items are Python numbers (not strings), or None if the respective
   channel was not supplied.
 - 'BITS': <data1>/<data2> contain a list of bit values in this MOSI/MISO data
   item, and for each of those also their respective start-/endsample numbers.
 - 'CS CHANGE': <data1> is the old CS# pin value, <data2> is the new value.
   Both data items are Python numbers (0/1), not strings. At the beginning of
   the decoding a packet is generated with <data1> = None and <data2> being the
   initial state of the CS# pin or None if the chip select pin is not supplied.

Examples:
 ['CS-CHANGE', None, 1]
 ['CS-CHANGE', 1, 0]
 ['DATA', 0xff, 0x3a]
 ['BITS', [[1, 80, 82], [1, 83, 84], [1, 85, 86], [1, 87, 88],
           [1, 89, 90], [1, 91, 92], [1, 93, 94], [1, 95, 96]],
          [[0, 80, 82], [1, 83, 84], [0, 85, 86], [1, 87, 88],
           [1, 89, 90], [1, 91, 92], [0, 93, 94], [0, 95, 96]]]
 ['DATA', 0x65, 0x00]
 ['DATA', 0xa8, None]
 ['DATA', None, 0x55]
 ['CS-CHANGE', 0, 1]
'''

# Key: (CPOL, CPHA). Value: SPI mode.
# Clock polarity (CPOL) = 0/1: Clock is low/high when inactive.
# Clock phase (CPHA) = 0/1: Data is valid on the leading/trailing clock edge.
spi_mode = {
    (0, 0): 0, # Mode 0
    (0, 1): 1, # Mode 1
    (1, 0): 2, # Mode 2
    (1, 1): 3, # Mode 3
}

class SamplerateError(Exception):
    pass

class ChannelError(Exception):
    pass

class Decoder(srd.Decoder):
    api_version = 2
    id = 'spi'
    name = 'SPI'
    longname = 'Serial Peripheral Interface'
    desc = 'Full-duplex, synchronous, serial bus.'
    license = 'gplv2+'
    inputs = ['logic']
    outputs = ['spi']
    channels = (
        {'id': 'clk', 'name': 'CLK', 'desc': 'Clock'},
    )
    optional_channels = (
        {'id': 'miso', 'name': 'MISO', 'desc': 'Master in, slave out'},
        {'id': 'mosi', 'name': 'MOSI', 'desc': 'Master out, slave in'},
        {'id': 'cs', 'name': 'CS#', 'desc': 'Chip-select'},
    )
    options = (
        {'id': 'cs_polarity', 'desc': 'CS# polarity', 'default': 'active-low',
            'values': ('active-low', 'active-high')},
        {'id': 'cpol', 'desc': 'Clock polarity', 'default': 0,
            'values': (0, 1)},
        {'id': 'cpha', 'desc': 'Clock phase', 'default': 0,
            'values': (0, 1)},
        {'id': 'bitorder', 'desc': 'Bit order',
            'default': 'msb-first', 'values': ('msb-first', 'lsb-first')},
        {'id': 'wordsize', 'desc': 'Word size', 'default': 8},
    )
    annotations = (
        ('miso-data', 'MISO data'),
        ('mosi-data', 'MOSI data'),
        ('miso-bits', 'MISO bits'),
        ('mosi-bits', 'MOSI bits'),
        ('warnings', 'Human-readable warnings'),
    )
    annotation_rows = (
        ('miso-data', 'MISO data', (0,)),
        ('miso-bits', 'MISO bits', (2,)),
        ('mosi-data', 'MOSI data', (1,)),
        ('mosi-bits', 'MOSI bits', (3,)),
        ('other', 'Other', (4,)),
    )
    binary = (
        ('miso', 'MISO'),
        ('mosi', 'MOSI'),
    )

    def __init__(self):
        self.samplerate = None
        self.oldclk = 1
        self.bitcount = 0
        self.misodata = self.mosidata = 0
        self.misobits = []
        self.mosibits = []
        self.ss_block = -1
        self.samplenum = -1
        self.cs_was_deasserted = False
        self.oldcs = None
        self.oldpins = None
        self.have_cs = self.have_miso = self.have_mosi = None
        self.no_cs_notification = False

    def metadata(self, key, value):
        if key == srd.SRD_CONF_SAMPLERATE:
            self.samplerate = value

    def start(self):
        self.out_python = self.register(srd.OUTPUT_PYTHON)
        self.out_ann = self.register(srd.OUTPUT_ANN)
        self.out_bin = self.register(srd.OUTPUT_BINARY)
        self.out_bitrate = self.register(srd.OUTPUT_META,
                meta=(int, 'Bitrate', 'Bitrate during transfers'))

    def putw(self, data):
        self.put(self.ss_block, self.samplenum, self.out_ann, data)

    def putdata(self):
        # Pass MISO and MOSI bits and then data to the next PD up the stack.
        so = self.misodata if self.have_miso else None
        si = self.mosidata if self.have_mosi else None
        so_bits = self.misobits if self.have_miso else None
        si_bits = self.mosibits if self.have_mosi else None

        if self.have_miso:
            ss, es = self.misobits[-1][1], self.misobits[0][2]
            self.put(ss, es, self.out_bin, (0, bytes([so])))
        if self.have_mosi:
            ss, es = self.mosibits[-1][1], self.mosibits[0][2]
            self.put(ss, es, self.out_bin, (1, bytes([si])))

        self.put(ss, es, self.out_python, ['BITS', si_bits, so_bits])
        self.put(ss, es, self.out_python, ['DATA', si, so])

        # Bit annotations.
        if self.have_miso:
            for bit in self.misobits:
                self.put(bit[1], bit[2], self.out_ann, [2, ['%d' % bit[0]]])
        if self.have_mosi:
            for bit in self.mosibits:
                self.put(bit[1], bit[2], self.out_ann, [3, ['%d' % bit[0]]])

        # Dataword annotations.
        if self.have_miso:
            self.put(ss, es, self.out_ann, [0, ['%02X' % self.misodata]])
        if self.have_mosi:
            self.put(ss, es, self.out_ann, [1, ['%02X' % self.mosidata]])

    def reset_decoder_state(self):
        self.misodata = 0 if self.have_miso else None
        self.mosidata = 0 if self.have_mosi else None
        self.misobits = [] if self.have_miso else None
        self.mosibits = [] if self.have_mosi else None
        self.bitcount = 0

    def cs_asserted(self, cs):
        active_low = (self.options['cs_polarity'] == 'active-low')
        return (cs == 0) if active_low else (cs == 1)

    def handle_bit(self, miso, mosi, clk, cs):
        # If this is the first bit of a dataword, save its sample number.
        if self.bitcount == 0:
            self.ss_block = self.samplenum
            self.cs_was_deasserted = \
                not self.cs_asserted(cs) if self.have_cs else False

        ws = self.options['wordsize']

        # Receive MISO bit into our shift register.
        if self.have_miso:
            if self.options['bitorder'] == 'msb-first':
                self.misodata |= miso << (ws - 1 - self.bitcount)
            else:
                self.misodata |= miso << self.bitcount

        # Receive MOSI bit into our shift register.
        if self.have_mosi:
            if self.options['bitorder'] == 'msb-first':
                self.mosidata |= mosi << (ws - 1 - self.bitcount)
            else:
                self.mosidata |= mosi << self.bitcount

        # Guesstimate the endsample for this bit (can be overridden below).
        es = self.samplenum
        if self.bitcount > 0:
            if self.have_miso:
                es += self.samplenum - self.misobits[0][1]
            elif self.have_mosi:
                es += self.samplenum - self.mosibits[0][1]

        if self.have_miso:
            self.misobits.insert(0, [miso, self.samplenum, es])
        if self.have_mosi:
            self.mosibits.insert(0, [mosi, self.samplenum, es])

        if self.bitcount > 0 and self.have_miso:
            self.misobits[1][2] = self.samplenum
        if self.bitcount > 0 and self.have_mosi:
            self.mosibits[1][2] = self.samplenum

        self.bitcount += 1

        # Continue to receive if not enough bits were received, yet.
        if self.bitcount != ws:
            return

        self.putdata()

        # Meta bitrate.
        elapsed = 1 / float(self.samplerate)
        elapsed *= (self.samplenum - self.ss_block + 1)
        bitrate = int(1 / elapsed * self.options['wordsize'])
        self.put(self.ss_block, self.samplenum, self.out_bitrate, bitrate)

        if self.have_cs and self.cs_was_deasserted:
            self.putw([4, ['CS# was deasserted during this data word!']])

        self.reset_decoder_state()

    def find_clk_edge(self, miso, mosi, clk, cs):
        if self.have_cs and self.oldcs != cs:
            # Send all CS# pin value changes.
            self.put(self.samplenum, self.samplenum, self.out_python,
                     ['CS-CHANGE', self.oldcs, cs])
            self.oldcs = cs
            # Reset decoder state when CS# changes (and the CS# pin is used).
            self.reset_decoder_state()

        # We only care about samples if CS# is asserted.
        if self.have_cs and not self.cs_asserted(cs):
            return

        # Ignore sample if the clock pin hasn't changed.
        if clk == self.oldclk:
            return

        self.oldclk = clk

        # Sample data on rising/falling clock edge (depends on mode).
        mode = spi_mode[self.options['cpol'], self.options['cpha']]
        if mode == 0 and clk == 0:   # Sample on rising clock edge
            return
        elif mode == 1 and clk == 1: # Sample on falling clock edge
            return
        elif mode == 2 and clk == 1: # Sample on falling clock edge
            return
        elif mode == 3 and clk == 0: # Sample on rising clock edge
            return

        # Found the correct clock edge, now get the SPI bit(s).
        self.handle_bit(miso, mosi, clk, cs)

    def decode(self, ss, es, data):
        if not self.samplerate:
            raise SamplerateError('Cannot decode without samplerate.')
        # Either MISO or MOSI can be omitted (but not both). CS# is optional.
        for (self.samplenum, pins) in data:

            # Ignore identical samples early on (for performance reasons).
            if self.oldpins == pins:
                continue
            self.oldpins, (clk, miso, mosi, cs) = pins, pins
            self.have_miso = (miso in (0, 1))
            self.have_mosi = (mosi in (0, 1))
            self.have_cs = (cs in (0, 1))

            # Either MISO or MOSI (but not both) can be omitted.
            if not (self.have_miso or self.have_mosi):
                raise ChannelError('Either MISO or MOSI (or both) pins required.')

            # Tell stacked decoders that we don't have a CS# signal.
            if not self.no_cs_notification and not self.have_cs:
                self.put(0, 0, self.out_python, ['CS-CHANGE', None, None])
                self.no_cs_notification = True

            self.find_clk_edge(miso, mosi, clk, cs)