Forum Discussion
Honored ContributorFixed Point VHDL Support in Quartus
I am asking how people have found the synthesis results with the new VHDL2008 package for fixed point. I have created a design that is a cascaded filter simulating a three phase RL load for a motor control application. I haven't synthesized it into quartus yet, but even if it compiles just fine, I am wondering if anyone in the community at large has had any issues with the implementation of these packages in Quartus?
This will be very influential in doing various types of controllers; PI, sliding mode, model reference adaptive control, etc . . . Thanks, James
library IEEE;
use IEEE.STD_LOGIC_1164.all;
use ieee.numeric_std.all;
use ieee.math_real.all;
use ieee.fixed_pkg.all;
entity ModelVoltage is
port(
MCLK : in STD_LOGIC;
HRST : in STD_LOGIC;
START : in std_logic;
VA : in STD_LOGIC;
VB : in STD_LOGIC;
VC : in STD_LOGIC;
DCBUSVOLTS : in STD_LOGIC_VECTOR(11 downto 0);
VAx : out sfixed(16 downto -16);
VBx : out sfixed(16 downto -16);
VCx : out sfixed(16 downto -16);
Vn : out sfixed(16 downto -16);
IA : out sfixed(16 downto -16);
IB : out sfixed(16 downto -16);
IC : out sfixed(16 downto -16);
DONE : out std_logic
);
end ModelVoltage;
architecture RTL of ModelVoltage is
type stateType is (S0,S1,S2,S3,S4,S5,S6,S7,S8);
signal state : stateType;
constant Cx: integer := 8;
constant Dx: integer := 16;
constant R : integer := 16;
constant N : integer := 16;
constant P : integer := 16;
constant M : integer := 40;
type abcType is record
a : sfixed(R downto -N);
b : sfixed(R downto -N);
c : sfixed(R downto -N);
n : sfixed(R downto -N);
nX : sfixed(R downto -N);
aR : sfixed(P downto -M);
bR : sfixed(P downto -M);
cR : sfixed(P downto -M);
aV : sfixed(R downto -N);
bV : sfixed(R downto -N);
cV : sfixed(R downto -N);
aVk1 : sfixed(R downto -N);
bVk1 : sfixed(R downto -N);
cVk1 : sfixed(R downto -N);
ak : sfixed(P downto -M);
bk : sfixed(P downto -M);
ck : sfixed(P downto -M);
ak1 : sfixed(P downto -M);
bk1 : sfixed(P downto -M);
ck1 : sfixed(P downto -M);
end record;
signal v : abcType;
signal i : abcType;
constant RecipThree : sfixed(8 downto -8) := to_sfixed(0.333,8,-8);
constant Rx : sfixed(8 downto -8) := to_sfixed(0.55,8,-8);
constant Ts2 : sfixed(8 downto -24) := to_sfixed(0.0004,8,-24);
begin
process(all) begin
if HRST then
v.a <= to_sfixed(0,R,-N);
v.b <= to_sfixed(0,R,-N);
v.c <= to_sfixed(0,R,-N);
elsif rising_edge(MCLK) then
if START then
if VA then
v.a <= to_sfixed(signed(DCBUSVOLTS),R,-N);
else
v.a <= to_sfixed(-200,R,-N);
end if;
if VB then
v.b <= to_sfixed(signed(DCBUSVOLTS),R,-N);
else
v.b <= to_sfixed(-200,R,-N);
end if;
if VC then
v.c <= to_sfixed(signed(DCBUSVOLTS),R,-N);
else
v.c <= to_sfixed(-200,R,-N);
end if;
end if;
end if;
end process;
VAx <= v.Av;
VBx <= v.Bv;
VCx <= v.Cv;
process(all) begin
if HRST then
v.n <= to_sfixed(0,R,-N);
elsif rising_edge(MCLK) then
if state = S2 then
v.n <= resize((v.a + v.b + v.c),R,-N);
end if;
end if;
end process;
process(all) begin
if HRST then
v.nX <= to_sfixed(0,R,-N);
elsif rising_edge(MCLK) then
if state = S3 then
v.nX <= resize(RecipThree*v.n,R,-N);
end if;
end if;
end process;
/*--------------------------------
Resistive voltage drop
--------------------------------*/
process(all) begin
if HRST then
v.aR <= to_sfixed(0,P,-M);
v.bR <= to_sfixed(0,P,-M);
v.cR <= to_sfixed(0,P,-M);
elsif rising_edge(MCLK) then
if state = S4 then
v.aR <= resize(Rx*i.ak,P,-M);
v.bR <= resize(Rx*i.bk,P,-M);
v.cR <= resize(Rx*i.ck,P,-M);
end if;
end if;
end process;
process(all) begin
if HRST then
v.aV <= to_sfixed(0,R,-N);
v.bV <= to_sfixed(0,R,-N);
v.cV <= to_sfixed(0,R,-N);
elsif rising_edge(MCLK) then
if state = S5 then
v.aV <= resize((v.a - v.aR - v.nX),R,-N);
v.bV <= resize((v.b - v.bR - v.nX),R,-N);
v.cV <= resize((v.c - v.cR - v.nX),R,-N);
end if;
end if;
end process;
process(all) begin
if HRST then
i.ak <= to_sfixed(0,P,-M);
i.bk <= to_sfixed(0,P,-M);
i.ck <= to_sfixed(0,P,-M);
elsif rising_edge(MCLK) then
if state = S6 then
i.ak <= resize(((v.aV + v.aVk1)*Ts2 + i.ak1),P,-M);
i.bk <= resize(((v.bV + v.bVk1)*Ts2 + i.bk1),P,-M);
i.ck <= resize(((v.cV + v.cVk1)*Ts2 + i.ck1),P,-M);
end if;
end if;
end process;
process(all) begin
if HRST then
i.ak1 <= to_sfixed(0,P,-M);
i.bk1 <= to_sfixed(0,P,-M);
i.ck1 <= to_sfixed(0,P,-M);
v.aVk1 <= to_sfixed(0,R,-N);
v.bVk1 <= to_sfixed(0,R,-N);
v.cVk1 <= to_sfixed(0,R,-N);
elsif rising_edge(MCLK) then
if state = S7 then
i.ak1 <= i.ak;
i.bk1 <= i.bk;
i.ck1 <= i.ck;
v.aVk1 <= v.aV;
v.bVk1 <= v.bV;
v.cVk1 <= v.cV;
end if;
end if;
end process;
IA <= i.ak(16 downto -16);
IB <= i.bk(16 downto -16);
IC <= i.ck(16 downto -16);
process(all) begin
if HRST then
state <= S0;
done <= '0';
elsif rising_edge(MCLK) then
case state is
when S0 =>
if START then
state <= S1;
else
state <= S0;
end if;
done <= '0';
when S1 =>
state <= S2;
when S2 =>
state <= S3;
when S3 =>
state <= S4;
when S4 =>
state <= S5;
when S5 =>
state <= S6;
when S6 =>
state <= S7;
when S7 =>
state <= S0;
done <= '1';
when others =>
null;
end case;
end if;
end process;
end RTL;18 Replies
Altera_ForumHi James,
I played with the fixed package briefly. Under Modelsim I could use the IEEE packages, but under Quartus I had to use David Bishop's _c.vhdl compatibility packages. http://www.eda.org/fphdl/ Other that that, they worked fine. (Though my tests were hardly exhaustive). Cheers, Dave- Altera_Forum
Dave,
That is excellent feedback. It gives me motivation to synthesize this design and others that I have thought about, and test them in the lab. For filter and controller design I think this will prove most useful. I just wish that Altera paid a little more attention to VHDL versus Verilog. Thanks. James - Altera_Forum
I have had great results with it (using the 93 compatible versions that is!). I've infered multipliers and RAMs using sfixed and ufixed types without a problem.
Target was an Arria 2. - Altera_Forum
Tricky, That is very good news. I take it you also used David Bishops package for actual compilation under Quartus? Best, James
- Altera_Forum
yes, those are the 93 compatible ones. please make an enhancement request for full vhdl 2008 support.
quartus is actually good at inference. I've made it infer rams from constrained integers and used character type as a address aswell (that was just an experiment, not a real design). - Altera_Forum
I have submitted a service request to Altera for full support of the fixed point package in VHDL2008. I will be curious to see what they have to say about this, and will let you know what they say. Thanks, James
- Altera_Forum
Tricky, in terms of an enhancement request for Altera, is there a specific channel to go through? I went through my support and it is not working too well. Thanks, James
- Altera_Forum
Hi James,
--- Quote Start --- in terms of an enhancement request for Altera, is there a specific channel to go through? I went through my support and it is not working too well. --- Quote End --- Do you have an FAE contact, at say Arrow, that you buy parts through? If so, then if you give them your SR number, they can internally apply pressure further up the support hierarchy. Cheers, Dave - Altera_Forum
Dave, Thanks for the feedback. I went ahead and corresponded on mysupport, where I had a case opened, and explicitly stated that I wanted an enhancement request for fixed point support in VHDL 2008 within Quartus. They said that they would pass it onto the software team; I also mentioned that it would be nice to have a more direct channel on the website for enhancement requests . . . Since I am new to Silicon Valley I haven't met my FAE's yet, but hopefully will soon. Thanks, James
- Altera_Forum
Hi James,
--- Quote Start --- ... I am new to Silicon Valley .... --- Quote End --- ... ahhh, Mountain View, such nice restaurants .... If you're also new to California, then make sure to visit Yosemite. If you feel like driving a little further (through to the other side of the park), you can come visit me, and I'll give you a tour ... http://www.mmarray.org/ Cheers, Dave
