greaseweazle-firmware/scripts/greaseweazle/track.py

# greaseweazle/track.py
#
# Written & released by Keir Fraser <keir.xen@gmail.com>
#
# This is free and unencumbered software released into the public domain.
# See the file COPYING for more details, or visit <http://unlicense.org>.

import binascii
import itertools as it
from bitarray import bitarray
from greaseweazle.flux import WriteoutFlux
from greaseweazle import optimised

# Precompensation to apply to a MasterTrack for writeout.
class Precomp:
    MFM = 0
    FM  = 1
    GCR = 2
    TYPESTRING = [ 'MFM', 'FM', 'GCR' ]
    def __str__(self):
        return "Precomp: %s, %dns" % (Precomp.TYPESTRING[self.type], self.ns)
    def __init__(self, type, ns):
        self.type = type
        self.ns = ns
    def apply(self, bits, bit_ticks, scale):
        t = self.ns * scale
        if self.type == Precomp.MFM:
            for i in bits.itersearch(bitarray('10100', endian='big')):
                bit_ticks[i+2] -= t
                bit_ticks[i+3] += t
            for i in bits.itersearch(bitarray('00101', endian='big')):
                bit_ticks[i+2] += t
                bit_ticks[i+3] -= t
        # This is primarily for GCR and FM which permit adjacent 1s (and
        # have correspondingly slower bit times). However it may be useful
        # for illegal MFM sequences too, especially on Amiga (custom syncwords,
        # 4us-bitcell tracks). Normal MFM should not trigger these patterns.
        for i in bits.itersearch(bitarray('110', endian='big')):
            bit_ticks[i+1] -= t
            bit_ticks[i+2] += t
        for i in bits.itersearch(bitarray('011', endian='big')):
            bit_ticks[i+1] += t
            bit_ticks[i+2] -= t


# A pristine representation of a track, from a codec and/or a perfect image.
class MasterTrack:

    @property
    def bitrate(self):
        return len(self.bits) / self.time_per_rev

    # bits: Track bitcell data, aligned to the write splice (bitarray or bytes)
    # time_per_rev: Time per revolution, in seconds (float)
    # bit_ticks: Per-bitcell time values, in unitless 'ticks'
    # splice: Location of the track splice, in bitcells, after the index
    # weak: List of (start, length) weak ranges
    def __init__(self, bits, time_per_rev, bit_ticks=None, splice=0, weak=[]):
        if isinstance(bits, bytes):
            self.bits = bitarray(endian='big')
            self.bits.frombytes(bits)
        else:
            self.bits = bits
        self.time_per_rev = time_per_rev
        self.bit_ticks = bit_ticks
        self.splice = splice
        self.weak = weak
        self.precomp = None
        self.force_random_weak = True

    def __str__(self):
        s = "\nMaster Track: splice @ %d\n" % self.splice
        s += (" %d bits, %.1f kbit/s"
              % (len(self.bits), self.bitrate))
        if self.bit_ticks:
            s += " (variable)"
        s += ("\n %.1f ms / rev (%.1f rpm)"
              % (self.time_per_rev * 1000, 60 / self.time_per_rev))
        if len(self.weak) > 0:
            s += "\n %d weak range" % len(self.weak)
            if len(self.weak) > 1: s += "s"
            s += ": " + ", ".join(str(n) for _,n in self.weak) + " bits"
        #s += str(binascii.hexlify(self.bits.tobytes()))
        return s

    def flux_for_writeout(self, cue_at_index=True):
        return self.flux(for_writeout=True, cue_at_index=cue_at_index)

    def flux(self, for_writeout=False, cue_at_index=True):

        # We're going to mess with the track data, so take a copy.
        bits = self.bits.copy()
        bitlen = len(bits)

        # Also copy the bit_ticks array (or create a dummy one), and remember
        # the total ticks that it contains.
        bit_ticks = self.bit_ticks.copy() if self.bit_ticks else [1] * bitlen
        ticks_to_index = sum(bit_ticks)

        # Weak regions need special processing for correct flux representation.
        for s,n in self.weak:
            e = s + n
            assert 0 < s < e < bitlen
            pattern = bitarray(endian="big")
            if n < 400 or self.force_random_weak:
                # Short weak regions are written with no flux transitions.
                # Actually we insert a flux transition every 32 bitcells, else
                # we risk triggering Greaseweazle's No Flux Area generator.
                pattern.frombytes(b"\x80\x00\x00\x00")
                bits[s:e] = (pattern * (n//32+1))[:n]
            else:
                # Long weak regions we present a fuzzy clock bit in an
                # otherwise normal byte (16 bits MFM). The byte may be
                # interpreted as
                # MFM 0001001010100101 = 12A5 = byte 0x43, or
                # MFM 0001001010010101 = 1295 = byte 0x47
                pattern.frombytes(b"\x12\xA5")
                bits[s:e] = (pattern * (n//16+1))[:n]
                for i in range(0, n-10, 16):
                    x, y = bit_ticks[s+i+10], bit_ticks[s+i+11]
                    bit_ticks[s+i+10], bit_ticks[s+i+11] = x+y*0.5, y*0.5
            # To prevent corrupting a preceding sync word by effectively
            # starting the weak region early, we start with a 1 if we just
            # clocked out a 0.
            bits[s] = not bits[s-1]
            # Similarly modify the last bit of the weak region.
            bits[e-1] = not(bits[e-2] or bits[e])

        if cue_at_index:
            # Rotate data to start at the index.
            index = -self.splice % bitlen
            if index != 0:
                bits = bits[index:] + bits[:index]
                bit_ticks = bit_ticks[index:] + bit_ticks[:index]
            splice_at_index = index < 4 or bitlen - index < 4
        else:
            splice_at_index = False

        if not for_writeout:
            # Do not extend the track for reliable writeout to disk.
            pass
        elif not cue_at_index:
            # We write the track wherever it may fall (uncued).
            # We stretch the track with extra header gap bytes, in case the
            # drive spins slow and we need more length to create an overlap.
            # Thus if the drive spins slow, the track gets a longer header.
            pos = 4
            # We stretch by 10 percent, which is way more than enough.
            rep = bitlen // (10 * 32)
            bit_ticks = bit_ticks[pos:pos+32] * rep + bit_ticks[pos:]
            bits = bits[pos:pos+32] * rep + bits[pos:]
        elif splice_at_index:
            # Splice is at the index (or within a few bitcells of it).
            # We stretch the track with extra footer gap bytes, in case the
            # drive motor spins slower than expected and we need more filler
            # to get us to the index pulse (where the write will terminate).
            # Thus if the drive spins slow, the track gets a longer footer.
            pos = (self.splice - 4) % bitlen
            # We stretch by 10 percent, which is way more than enough.
            rep = bitlen // (10 * 32)
            bit_ticks = bit_ticks[:pos] + bit_ticks[pos-32:pos] * rep
            bits = bits[:pos] + bits[pos-32:pos] * rep
        else:
            # Splice is not at the index. We will write more than one
            # revolution, and terminate the second revolution at the splice.
            # For the first revolution we repeat the track header *backwards*
            # to the very start of the write. This is in case the drive motor
            # spins slower than expected and the write ends before the original
            # splice position.
            # Thus if the drive spins slow, the track gets a longer header.
            bit_ticks += bit_ticks[:self.splice-4]
            bits += bits[:self.splice-4]
            pos = self.splice+4
            fill_pattern = bits[pos:pos+32]
            while pos >= 32:
                pos -= 32
                bits[pos:pos+32] = fill_pattern

        if for_writeout and self.precomp is not None:
            self.precomp.apply(bits, bit_ticks,
                               ticks_to_index / (self.time_per_rev*1e9))

        # Convert the stretched track data into flux.
        bit_ticks_i = iter(bit_ticks)
        flux_list = []
        flux_ticks = 0
        for bit in bits:
            flux_ticks += next(bit_ticks_i)
            if bit:
                flux_list.append(flux_ticks)
                flux_ticks = 0
        if flux_ticks and for_writeout:
            flux_list.append(flux_ticks)

        # Package up the flux for return.
        flux = WriteoutFlux(ticks_to_index, flux_list,
                            ticks_to_index / self.time_per_rev,
                            index_cued = cue_at_index,
                            terminate_at_index = splice_at_index)
        return flux


# Track data generated from flux.
class RawTrack:

    def __init__(self, clock, data):
        self.clock = clock
        self.clock_max_adj = 0.10
        self.pll_period_adj = 0.05
        self.pll_phase_adj = 0.60
        self.bitarray = bitarray(endian='big')
        self.timearray = []
        self.revolutions = []
        self.import_flux_data(data)


    def __str__(self):
        s = "\nRaw Track: %d revolutions\n" % len(self.revolutions)
        for rev in range(len(self.revolutions)):
            b, _ = self.get_revolution(rev)
            s += "Revolution %u (%u bits): " % (rev, len(b))
            s += str(binascii.hexlify(b.tobytes())) + "\n"
        b = self.bitarray[sum(self.revolutions):]
        s += "Tail (%u bits): " % (len(b))
        s += str(binascii.hexlify(b.tobytes())) + "\n"
        return s[:-1]


    def get_revolution(self, nr):
        start = sum(self.revolutions[:nr])
        end = start + self.revolutions[nr]
        return self.bitarray[start:end], self.timearray[start:end]


    def get_all_data(self):
        return self.bitarray, self.timearray


    def import_flux_data(self, data):

        flux = data.flux()
        freq = flux.sample_freq

        clock = self.clock
        clock_min = self.clock * (1 - self.clock_max_adj)
        clock_max = self.clock * (1 + self.clock_max_adj)

        index_iter = it.chain(iter(map(lambda x: x/freq, flux.index_list)),
                              [float('inf')])

        # Make sure there's enough time in the flux list to cover all
        # revolutions by appending a "large enough" final flux value.
        tail = max(0, sum(flux.index_list) - sum(flux.list) + clock*freq*2)
        flux_iter = it.chain(flux.list, [tail])

        try:
            optimised.flux_to_bitcells(
                self.bitarray, self.timearray, self.revolutions,
                index_iter, flux_iter,
                freq, clock, clock_min, clock_max,
                self.pll_period_adj, self.pll_phase_adj)
        except AttributeError:
            flux_to_bitcells(
                self.bitarray, self.timearray, self.revolutions,
                index_iter, flux_iter,
                freq, clock, clock_min, clock_max,
                self.pll_period_adj, self.pll_phase_adj)

            
def flux_to_bitcells(bit_array, time_array, revolutions,
                     index_iter, flux_iter,
                     freq, clock_centre, clock_min, clock_max,
                     pll_period_adj, pll_phase_adj):

    nbits = 0
    ticks = 0.0
    clock = clock_centre
    to_index = next(index_iter)

    for x in flux_iter:

        # Gather enough ticks to generate at least one bitcell.
        ticks += x / freq
        if ticks < clock/2:
            continue

        # Clock out zero or more 0s, followed by a 1.
        zeros = 0
        while True:

            # Check if we cross the index mark.
            to_index -= clock
            if to_index < 0:
                revolutions.append(nbits)
                nbits = 0
                to_index += next(index_iter)

            nbits += 1
            ticks -= clock
            time_array.append(clock)
            if ticks >= clock/2:
                zeros += 1
                bit_array.append(False)
            else:
                bit_array.append(True)
                break

        # PLL: Adjust clock frequency according to phase mismatch.
        if zeros <= 3:
            # In sync: adjust clock by a fraction of the phase mismatch.
            clock += ticks * pll_period_adj
        else:
            # Out of sync: adjust clock towards centre.
            clock += (clock_centre - clock) * pll_period_adj
        # Clamp the clock's adjustment range.
        clock = min(max(clock, clock_min), clock_max)
        # PLL: Adjust clock phase according to mismatch.
        new_ticks = ticks * (1 - pll_phase_adj)
        time_array[-1] += ticks - new_ticks
        ticks = new_ticks

# Local variables:
# python-indent: 4
# End: