From 2f2b9b319fd36b6f9ccd98271c8fbe60b83cb982 Mon Sep 17 00:00:00 2001 From: Florent Kermarrec Date: Sat, 11 May 2019 09:36:53 +0200 Subject: [PATCH] soc/cores: remove cordic Cordic is useful for DSP cores but not as a Soc building block. --- litex/soc/cores/cordic.py | 361 -------------------------------------- 1 file changed, 361 deletions(-) delete mode 100644 litex/soc/cores/cordic.py diff --git a/litex/soc/cores/cordic.py b/litex/soc/cores/cordic.py deleted file mode 100644 index 14a928532..000000000 --- a/litex/soc/cores/cordic.py +++ /dev/null @@ -1,361 +0,0 @@ -# Copyright 2014-2015 Robert Jordens -# -# 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 . - -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)) - ) - ]