joris
/
vhdl-sincos-gen
1
0
Fork 0
Code Issues Pull Requests Activity

Fix mistakes in changes related to phase_extrabits.

This commit is contained in:
Joris van Rantwijk 2016-04-20 23:10:11 +02:00
parent ba096abf16
commit fe5dfa9133
1 changed files with 7 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
rtl/sincos_gen.vhdl
View File

@ -245,7 +245,7 @@ begin
-- Extract phase remainder as signed number
-- (by simply inverting the sign bit).
v1_rphase(rphase_bits-1 downto 0) :=
v1_rphase(rphase_bits-1) :=
not in_phase(rphase_bits-1);
v1_rphase(rphase_bits-2 downto 0) :=
signed(in_phase(rphase_bits-2 downto 0));
@ -255,9 +255,10 @@ begin
-- Multiply phase remainder by Pi/2, first step.
-- t1 = rphase + (rphase >> 4)
-- (left-shift to add extra phase bits to increase accuracy)
-- (add extra '0' bits to increase accuracy)
-- (apply rounding constant for truncation due to shift)
v1_xphase := shift_left(v1_rphase, phase_extrabits);
v1_xphase(v1_xphase'high downto phase_extrabits) := v1_rphase;
v1_xphase(phase_extrabits-1 downto 0) := (others => '0');
r1_dphase <= resize(v1_xphase, dphase_bits) +
resize(shift_right(v1_xphase, 4), dphase_bits) +
signed("0" & v1_xphase(3 downto 3));
@ -291,9 +292,10 @@ begin
-- Multiply phase remainder by Pi/2, final step.
-- dphase = t2 + (rphase >> 1)
-- (left-shift to add extra phase bits to increase accuracy)
-- (add extra '0' bits to increase accuracy)
-- (apply rounding constant for truncation due to shift)
v3_xphase := shift_left(r2_rphase, phase_extrabits);
v3_xphase(v3_xphase'high downto phase_extrabits) := r2_rphase;
v3_xphase(phase_extrabits-1 downto 0) := (others => '0');
v3_dphase := r2_dphase +
resize(shift_right(v3_xphase, 1), dphase_bits) +
signed("0" & v3_xphase(0 downto 0));