Connecting std_logic to std_logic_vector in component declaration

[Chris Jones]

Hello,

I am using the System Generator tool from Xilinx to generate VHDL code
for a DSP design. The Sys Gen tool creates components that have all
signals defined as std_logic_vector even if they are a single bit, (0
downto 0).

At the next higher level, I had to create a bunch of dummy std_logic
vector signals that is assigned from a std_logic and then I use the
dummy signal in the component definition.

I did this to clear up errors pertaining to mixing types.

See code below ...


Is there a cleaner way to solve this problem?

Thanks,

Chris Jones
Engenium Technologies
(e-mail address removed)


----------------------------------------------

U3_MODEM: flex_modem
port map (
adc => ADC,
addrbus => Address,
ctrlregdataout => CtrlRegDataOut,
ctrlregen => CtrlRegEn_slv,
datain => DataIn,
dspwrite => WrPulse_slv,
profileen => ProfileEn_slv,
profiledataout => ProfileDataOut,
reqdataword => ReqDataWord_slv,
reset => (others => '0'),
rxdataout => RxDataOut,
rxgainhi => open,
txrxen => TxRxEn_slv);


-- Convert signals to standard_logic_vector in order
-- to connect to component
WrPulse_slv(0) <= WrPulse;
CtrlRegEn_slv(0) <= CtrlRegEn;
TxRxEn_slv(0) <= TxRxEn;
ProfileEn_slv(0) <= ProfileEn;

 

[Jonathan Bromley]

I am using the System Generator tool from Xilinx to generate VHDL code
for a DSP design. The Sys Gen tool creates components that have all
signals defined as std_logic_vector even if they are a single bit, (0
downto 0).

At the next higher level, I had to create a bunch of dummy std_logic
vector signals that is assigned from a std_logic and then I use the
dummy signal in the component definition. [...]

Is there a cleaner way to solve this problem?

Yes; use polymorphic conversion functions on the port map.

-- input conversion ---------------------------------------

function vectorize(s: std_logic) return std_logic_vector is
variable v: std_logic_vector(0 downto 0);
begin
v(0) := s;
return v;
end;

function vectorize(v: std_logic_vector) return std_logic_vector is
begin
return v;
end;

----Output conversion ---------------------------------------

.... can be very similar ...

function scalarize(v: in std_logic_vector) return std_ulogic is
begin
assert v'length = 1
report "scalarize: output port must be single bit!"
severity FAILURE;
return v(v'LEFT);
end;

-------------------------------------------------------------

OK, armed with these functions (in a package, I hope) you
can connect up either a std_logic or a std_logic_vector
to any suitable 1-bit vector port:

component blah
port (
a: in std_logic_vector(0 downto 0);
b: in std_logic_vector(0 downto 0);
c: out std_logic_vector(0 downto 0)
);
end component;

.....

signal s1, s2: std_logic;
signal v: std_logic_vector(0 downto 0);
--instantiation...
I1: blah port map (
a => vectorize(s1),
b => vectorize(v),
scalarize(c) => s2);

The conversion vectorize(v) is, of course, quite unnecessary;
but it has a certain symmetrical appeal, don't you think?

Cooler yet, you could make the component have ports to suit
your testbench, leave the entity with its silly one-bit
vector ports, and build a port map with conversion
functions in a configuration.

There's a really nice description of port-map conversion
functions in Ben Cohen's "VHDL Answers to Frequently
Asked Questions".
--

Jonathan Bromley, Consultant

DOULOS - Developing Design Know-how
VHDL * Verilog * SystemC * Perl * Tcl/Tk * Verification * Project Services

Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, Hampshire, BH24 1AW, UK
Tel: +44 (0)1425 471223 mail: (e-mail address removed)
Fax: +44 (0)1425 471573 Web: http://www.doulos.com

The contents of this message may contain personal views which
are not the views of Doulos Ltd., unless specifically stated.

 

[Jim Lewis]

You should also be able to index array ports in
the association:

signal s1, s2: std_logic;
signal v: std_logic_vector(0 downto 0);

--instantiation...
I1: blah port map (
a(a'left) => s1,
b => v,
c(c'left) => s2);


Cheers,
Jim

An additional comment follows below.
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jim Lewis
Director of Training mailto:[email protected]
SynthWorks Design Inc. http://www.SynthWorks.com
1-503-590-4787

Expert VHDL Training for Hardware Design and Verification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Jonathan Bromley wrote:

Cooler yet, you could make the component have ports to suit
your testbench, leave the entity with its silly one-bit
vector ports, and build a port map with conversion
functions in a configuration.

Or of course you could also do bit association in the port
map in the configuration. This one is a little closer to
my heart as we did this after picking an ASIC vendor when
we were well into a project and learned that the ASIC
vendor required bit ports on the top level of the ASIC.
So rather than switching the ports of our design to bit
ports, we let the synthesis tool do this and fixed the
port mapping in the configuration that ran the gate
simulations.

However, in hind site, it would have been easier to
change the design source to bit ports rather than fussing
with the configurations. We also used configurations for
selecting test cases and mapping generics. The additional
requirement of either mapping the gate design with bit
ports or the original design with array ports ended up
doubling the number of configurations we had.