+++ /dev/null
-# Copyright 2014-2015 Robert Jordens <jordens@gmail.com>
-#
-# This file is part of redpid.
-#
-# redpid 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 3 of the License, or
-# (at your option) any later version.
-#
-# redpid 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 redpid. If not, see <http://www.gnu.org/licenses/>.
-
-from math import atan, atanh, log, sqrt, pi
-
-from migen import *
-
-
-class TwoQuadrantCordic(Module):
- """Coordinate rotation digital computer
-
- Trigonometric, and arithmetic functions implemented using
- additions/subtractions and shifts.
-
- http://eprints.soton.ac.uk/267873/1/tcas1_cordic_review.pdf
-
- http://www.andraka.com/files/crdcsrvy.pdf
-
- http://zatto.free.fr/manual/Volder_CORDIC.pdf
-
- The way the CORDIC is executed is controlled by `eval_mode`.
- If `"iterative"` the stages are iteratively evaluated, one per clock
- cycle. This mode uses the least amount of registers, but has the
- lowest throughput and highest latency. If `"pipelined"` all stages
- are executed in every clock cycle but separated by registers. This
- mode has full throughput but uses many registers and has large
- latency. If `"combinatorial"`, there are no registers, throughput is
- maximal and latency is zero. `"pipelined"` and `"combinatorial"` use
- the same number of shifters and adders.
-
- The type of trigonometric/arithmetic function is determined by
- `cordic_mode` and `func_mode`. :math:`g` is the gain of the CORDIC.
-
- * rotate-circular: rotate the vector `(xi, yi)` by an angle `zi`.
- Used to calculate trigonometric functions, `sin(), cos(),
- tan() = sin()/cos()`, or to perform polar-to-cartesian coordinate
- transformation:
-
- .. math::
- x_o = g \\cos(z_i) x_i - g \\sin(z_i) y_i
-
- y_o = g \\sin(z_i) x_i + g \\cos(z_i) y_i
-
- * vector-circular: determine length and angle of the vector
- `(xi, yi)`. Used to calculate `arctan(), sqrt()` or
- to perform cartesian-to-polar transformation:
-
- .. math::
- x_o = g\\sqrt{x_i^2 + y_i^2}
-
- z_o = z_i + \\tan^{-1}(y_i/x_i)
-
- * rotate-hyperbolic: hyperbolic functions of `zi`. Used to
- calculate hyperbolic functions, `sinh, cosh, tanh = cosh/sinh,
- exp = cosh + sinh`:
-
- .. math::
- x_o = g \\cosh(z_i) x_i + g \\sinh(z_i) y_i
-
- y_o = g \\sinh(z_i) x_i + g \\cosh(z_i) z_i
-
- * vector-hyperbolic: natural logarithm `ln(), arctanh()`, and
- `sqrt()`. Use `x_i = a + b` and `y_i = a - b` to obtain `2*
- sqrt(a*b)` and `ln(a/b)/2`:
-
- .. math::
- x_o = g\\sqrt{x_i^2 - y_i^2}
-
- z_o = z_i + \\tanh^{-1}(y_i/x_i)
-
- * rotate-linear: multiply and accumulate (not a very good
- multiplier implementation):
-
- .. math::
- y_o = g(y_i + x_i z_i)
-
- * vector-linear: divide and accumulate:
-
- .. math::
- z_o = g(z_i + y_i/x_i)
-
- Parameters
- ----------
- width : int
- Bit width of the input and output signals. Defaults to 16. Input
- and output signals are signed.
- widthz : int
- Bit with of `zi` and `zo`. Defaults to the `width`.
- stages : int or None
- Number of CORDIC incremental rotation stages. Defaults to
- `width + min(1, guard)`.
- guard : int or None
- Add guard bits to the intermediate signals. If `None`,
- defaults to `guard = log2(width)` which guarantees accuracy
- to `width` bits.
- eval_mode : str, {"iterative", "pipelined", "combinatorial"}
- cordic_mode : str, {"rotate", "vector"}
- func_mode : str, {"circular", "linear", "hyperbolic"}
- Evaluation and arithmetic mode. See above.
-
- Attributes
- ----------
- xi, yi, zi : Signal(width), in
- Input values, signed.
- xo, yo, zo : Signal(width), out
- Output values, signed.
- new_out : Signal(1), out
- Asserted if output values are freshly updated in the current
- cycle.
- new_in : Signal(1), out
- Asserted if new input values are being read in the next cycle.
- zmax : float
- `zi` and `zo` normalization factor. Floating point `zmax`
- corresponds to `1<<(widthz - 1)`. `x` and `y` are scaled such
- that floating point `1` corresponds to `1<<(width - 1)`.
- gain : float
- Cumulative, intrinsic gain and scaling factor. In circular mode
- `sqrt(xi**2 + yi**2)` should be no larger than `2**(width - 1)/gain`
- to prevent overflow. Additionally, in hyperbolic and linear mode,
- the operation itself can cause overflow.
- interval : int
- Output interval in clock cycles. Inverse throughput.
- latency : int
- Input-to-output latency. The result corresponding to the inputs
- appears at the outputs `latency` cycles later.
-
- Notes
- -----
-
- Each stage `i` in the CORDIC performs the following operation:
-
- .. math::
- x_{i+1} = x_i - m d_i y_i r^{-s_{m,i}},
-
- y_{i+1} = y_i + d_i x_i r^{-s_{m,i}},
-
- z_{i+1} = z_i - d_i a_{m,i},
-
- where:
-
- * :math:`d_i`: clockwise or counterclockwise, determined by
- `sign(z_i)` in rotate mode or `sign(-y_i)` in vector mode.
-
- * :math:`r`: radix of the number system (2)
-
- * :math:`m`: 1: circular, 0: linear, -1: hyperbolic
-
- * :math:`s_{m,i}`: non decreasing integer shift sequence
-
- * :math:`a_{m,i}`: elemetary rotation angle: :math:`a_{m,i} =
- \\tan^{-1}(\\sqrt{m} s_{m,i})/\\sqrt{m}`.
- """
- def __init__(self, width=16, widthz=None, stages=None, guard=0,
- eval_mode="iterative", cordic_mode="rotate",
- func_mode="circular"):
- # validate parameters
- assert eval_mode in ("combinatorial", "pipelined", "iterative")
- assert cordic_mode in ("rotate", "vector")
- assert func_mode in ("circular", "linear", "hyperbolic")
- self.cordic_mode = cordic_mode
- self.func_mode = func_mode
- if guard is None:
- # guard bits to guarantee "width" accuracy
- guard = int(log(width)/log(2))
- if widthz is None:
- widthz = width
- if stages is None:
- stages = width + min(1, guard) # cuts error below LSB
-
- # input output interface
- self.xi = Signal((width, True))
- self.yi = Signal((width, True))
- self.zi = Signal((widthz, True))
- self.xo = Signal((width, True))
- self.yo = Signal((width, True))
- self.zo = Signal((widthz, True))
- self.new_in = Signal()
- self.new_out = Signal()
-
- ###
-
- a, s, self.zmax, self.gain = self._constants(stages, widthz + guard)
- stages = len(a) # may have increased due to repetitions
-
- if eval_mode == "iterative":
- num_sig = 3
- self.interval = stages + 1
- self.latency = stages + 2
- else:
- num_sig = stages + 1
- self.interval = 1
- if eval_mode == "pipelined":
- self.latency = stages
- else: # combinatorial
- self.latency = 0
-
- # inter-stage signals
- x = [Signal((width + guard, True), reset_less=True)
- for i in range(num_sig)]
- y = [Signal((width + guard, True), reset_less=True)
- for i in range(num_sig)]
- z = [Signal((widthz + guard, True), reset_less=True)
- for i in range(num_sig)]
-
- # hook up inputs and outputs to the first and last inter-stage
- # signals
- self.comb += [
- x[0].eq(self.xi << guard),
- y[0].eq(self.yi << guard),
- z[0].eq(self.zi << guard),
- self.xo.eq(x[-1] >> guard),
- self.yo.eq(y[-1] >> guard),
- self.zo.eq(z[-1] >> guard),
- ]
-
- if eval_mode == "iterative":
- # We afford one additional iteration for in/out.
- i = Signal(max=stages + 1)
- self.comb += [
- self.new_in.eq(i == stages),
- self.new_out.eq(i == 1),
- ]
- ai = Signal((widthz + guard, True), reset_less=True)
- self.sync += ai.eq(Array(a)[i])
- if range(stages) == s:
- si = i - 1 # shortcut if no stage repetitions
- else:
- si = Signal(max=stages + 1, reset_less=True)
- self.sync += si.eq(Array(s)[i])
- xi, yi, zi = x[1], y[1], z[1]
- self.sync += [
- self._stage(xi, yi, zi, xi, yi, zi, si, ai),
- i.eq(i + 1),
- If(i == stages,
- i.eq(0),
- ),
- If(i == 0,
- x[2].eq(xi), y[2].eq(yi), z[2].eq(zi),
- xi.eq(x[0]), yi.eq(y[0]), zi.eq(z[0]),
- )
- ]
- else:
- self.comb += [
- self.new_out.eq(1),
- self.new_in.eq(1),
- ]
- for i, si in enumerate(s):
- stmt = self._stage(x[i], y[i], z[i],
- x[i + 1], y[i + 1], z[i + 1],
- si, a[i])
- if eval_mode == "pipelined":
- self.sync += stmt
- else: # combinatorial
- self.comb += stmt
-
- def _constants(self, stages, bits):
- if self.func_mode == "circular":
- s = range(stages)
- a = [atan(2**-i) for i in s]
- g = [sqrt(1 + 2**(-2*i)) for i in s]
- #zmax = sum(a)
- # use pi anyway as the input z can cause overflow
- # and we need the range for quadrant mapping
- zmax = pi
- elif self.func_mode == "linear":
- s = range(stages)
- a = [2**-i for i in s]
- g = [1 for i in s]
- #zmax = sum(a)
- # use 2 anyway as this simplifies a and scaling
- zmax = 2.
- else: # hyperbolic
- s = []
- # need to repeat some stages:
- j = 4
- for i in range(stages):
- if i == j:
- s.append(j)
- j = 3*j + 1
- s.append(i + 1)
- a = [atanh(2**-i) for i in s]
- g = [sqrt(1 - 2**(-2*i)) for i in s]
- zmax = sum(a)*2
- # round here helps the width=2**i - 1 case but hurts the
- # important width=2**i case
- cast = int
- if log(bits)/log(2) % 1:
- cast = round
- a = [cast(ai*2**(bits - 1)/zmax) for ai in a]
- gain = 1.
- for gi in g:
- gain *= gi
- return a, s, zmax, gain
-
- def _stage(self, xi, yi, zi, xo, yo, zo, i, ai):
- dir = Signal()
- if self.cordic_mode == "rotate":
- self.comb += dir.eq(zi < 0)
- else: # vector
- self.comb += dir.eq(yi >= 0)
- dx = yi >> i
- dy = xi >> i
- dz = ai
- if self.func_mode == "linear":
- dx = 0
- elif self.func_mode == "hyperbolic":
- dx = -dx
- stmt = [
- xo.eq(xi + Mux(dir, dx, -dx)),
- yo.eq(yi + Mux(dir, -dy, dy)),
- zo.eq(zi + Mux(dir, dz, -dz))
- ]
- return stmt
-
-
-class Cordic(TwoQuadrantCordic):
- """Four-quadrant CORDIC
-
- Same as :class:`TwoQuadrantCordic` but with support and convergence
- for `abs(zi) > pi/2 in circular rotate mode or `xi < 0` in circular
- vector mode.
- """
- def __init__(self, **kwargs):
- TwoQuadrantCordic.__init__(self, **kwargs)
- if self.func_mode != "circular":
- return # no need to remap quadrants
-
- cxi, cyi, czi = self.xi, self.yi, self.zi
- self.xi = xi = Signal.like(cxi)
- self.yi = yi = Signal.like(cyi)
- self.zi = zi = Signal.like(czi)
-
- ###
-
- q = Signal()
- if self.cordic_mode == "rotate":
- self.comb += q.eq(zi[-2] ^ zi[-1])
- else: # vector
- self.comb += q.eq(xi < 0)
- self.comb += [
- If(q,
- Cat(cxi, cyi, czi).eq(
- Cat(-xi, -yi, zi + (1 << len(zi) - 1)))
- ).Else(
- Cat(cxi, cyi, czi).eq(Cat(xi, yi, zi))
- )
- ]
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