State definition and display: literal vs. symbolic in ModelSim

[Paul Urbanus]

I have a design with a state machine whose present state is also an
output at the top level. At the top level (corresponding to I/O pins),
this state signal is an slv. The values for the various states are also
defined in the FPGA application interface spec.

I have explicitly defined the various states as constants, but when I
look at 'dips_ctrl_state' in ModelSim's waveform viewer, I can't get it
to use the symbolic names I've assigned when I set the radix to
'symbolic'. For instance, I would like to see 'CS_RESET' instead of '0'.

Here's the code I have to define the various states and propagate the
state to the top level.

======== from the entity port declarations ==========
disp_ctrl_state : out std_logic_vector(2 downto 0);

======== from the architecture declarations ========
--
-- Display Control State (to reformatter)
--
signal i_disp_ctrl_state : std_logic_vector(2 downto 0);
constant CS_RESET : std_logic_vector(2 downto 0) := "000";
constant CS_IDLE : std_logic_vector(2 downto 0) := "001";
constant CS_LOAD_DMD : std_logic_vector(2 downto 0) := "010";
constant CS_RDY_EXP : std_logic_vector(2 downto 0) := "011";
constant CS_EXPOSING : std_logic_vector(2 downto 0) := "100";
constant CS_RDY_CLR : std_logic_vector(2 downto 0) := "101";
constant CS_PARKED : std_logic_vector(2 downto 0) := "110";
constant CS_RESVD : std_logic_vector(2 downto 0) := "111";

======== from the architecture code ========
disp_ctrl_state <= i_disp_ctrl_state;


If I try and assign the states be defining a unique state type and
enumerating the states, then I can't get the explicit state values I
need to meet the interface spec. And I get an (expected) type mismatch
when I try and assign the state type to the std_logic_vector at the top
level. However, the symbolic waveform display works great.

======== from the entity port declarations ==========
disp_ctrl_state : out std_logic_vector(2 downto 0);

======== from the architecture declarations ========
--
-- Display Control State (to reformatter)
--
-- type i_disp_ctrl_state_type is (
-- CS_RESET,
-- CS_IDLE,
-- CS_LOAD_DMD,
-- CS_RDY_EXP,
-- CS_EXPOSING,
-- CS_RDY_CLR,
-- CS_PARKED,
-- CS_RESVD );
-- signal i_disp_ctrl_state : i_disp_ctrl_state_type;

======== from the architecture code ========
disp_ctrl_state <= i_disp_ctrl_state;


QUESTION: Is there a way to get ModelSim to show my std_logic_vector
state values symbolically?

QUESTION: If not, is there a way I can assign literal values to the
state types so I can view them symbolically in ModelSim? Can I cast them
to std_logic_vector before assigning them to the top-level I/O pins, so
I can at least view the internal state symbolically?

TIA
Urb

 

[Mike Treseler]

See page 26 of
http://www.hep.wisc.edu/~gowrisha/Tutorial.pdf

--- Mike Treseler

 

[Paul Urbanus]

See page 26 of
http://www.hep.wisc.edu/~gowrisha/Tutorial.pdf

--- Mike Treseler

Mike,

Thanks for the pointer, but a newbie tutorial on ModelSim isn't what I
need. If you re-read my post, you'll see that I'm asking a deeper
question, the answer which is not "select the 'symbolic' radix for the
signal(s) in question, as indicated in the tutorial".

What I'm asking is how to get a symbolic display of a state if the
signal is a std_logic_vector and the states are defined as constants.

Or, how to assign explicit slv values to an enumerated type such as a
state type.

I know that I can brute force this and add a case statement to my code
that will allow me to convert the enumerated state type to an slv, which
I can than pass to the top level I/O pins. Then, I can view state
symbolically by just displaying the enumerated state signal from inside
the design. However, I was looking for a more elegant solution, which
may not exist.

Urb

 

[Mike Treseler]

Thanks for the pointer, but a newbie tutorial on ModelSim isn't what I
need.

Did you see the bit on virtual signals?
That is a modelsim feature that might do what you want.

You also might try using a vhdl record type,
I think modelsim handles those identifiers reasonably.

-- Mike Treseler

 

[Tim Hubberstey]

Mike,

Thanks for the pointer, but a newbie tutorial on ModelSim isn't what I
need. If you re-read my post, you'll see that I'm asking a deeper
question, the answer which is not "select the 'symbolic' radix for the
signal(s) in question, as indicated in the tutorial".

What I'm asking is how to get a symbolic display of a state if the
signal is a std_logic_vector and the states are defined as constants.

Or, how to assign explicit slv values to an enumerated type such as a
state type.

I know that I can brute force this and add a case statement to my code
that will allow me to convert the enumerated state type to an slv, which
I can than pass to the top level I/O pins. Then, I can view state
symbolically by just displaying the enumerated state signal from inside
the design. However, I was looking for a more elegant solution, which
may not exist.

This is not directly possible for a couple of reasons:

Firstly, you've got a scoping issue. The constants you are referring to
are defined *inside* the architecture while the pins you want to observe
are *outside*. As a result, the constants will not be "visible".

Secondly, constants and type definitions are in separate namespaces.
This means that even though you have enumerated your states with the
same names as your constants, they are NOT the same. However, there is a
real possibility that a synthesizer will not like your code *because*
you've used the same names (synthesizers tend to be excessively picky).

The cleanest way to do this, IMO, is to create an independent monitor
entity that understands the coding of your SLVs and outputs an
appropriate enumerated type. I suggest you move your constants into a
package and include the package in both your code and the monitor.

The way I often deal with this is to "cheat" and observe the enumerated
value inside the architecture. Unfortunately, this only works for RTL
and if you want to simulate gate-level code, you're stuck with a monitor
entity.