Delta Time 'View' in ModelSim

Introduction

For some people learning the language the concept of delta time is one of the most tough to understand. It's not the objective of this article to discuss about delta delay, but to let you to know the tools available in ModelSim to 'see' the delta delays.

How to 'see' the delta delays

I'll explain in few steps the procedures to follow to find out how many delta delays happens until a signal has an stable value.
First, here is the simple code I'll use

 1 library ieee;
 2 use eee.std_logic_1164.all;
 3
 4 entity aoi is
 5 port(A, B, C, D: in std_logic;
 6      E         : out std_logic);
 7 end aoi;
 8
 9 architecture beha4 of aoi is
10 signal O1, O2, O3:std_logic;
11
12 begin
13 b4: process(A, B, C, D, O1, O2, O3)
14  begin
15   E  <= not O3;
16   O1 <= A and B;  
17   O2 <= C and D;  
18   O3 <= O1 or O2;
19 end process b4;
20 end dflow1;

and this is the simple test bench used

 1 library ieee;
 2 use eee.std_logic_1164.all;
 3
 4 entity aoi_tb is
 5 end aoi_tb;
 6
 7 architecture test of aoi_tb is
 8 signal O1, O2, O3   : std_logic;
 9 signal a, b, c, d, e: std_logic;
10 component  aoi is
11   port(A, B, C, D: in std_logic; E: out std_logic);
12 end component;
13
14 begin
15    a <= '0', '1' after 6 ns;
16    b <= '0', '1' after 5 ns, '0' after 8 ns;
17    c <= '0', '1' after 7 ns;
18    d <= '0';
19
20 uut: aoi  port map(
21   E => e, a => a ,b => b ,c => c, d => d
22   );
23 end test;
24

Once you have executed the test bench, the Wave window will show the respective waveform, as you can see in this figure (a point to keep in mind is that you will likely have to add the internal signals, in this case O1, O2, O3, to the Wave window):

So, if you want to know the delta delays that happened at the simulation time 8 ns, you have to: 
1- Place a cursor on the 8 ns simulation time.
2- Click on the 'Expanded Time Delta Mode" button

3- Click on the "Expand Time at Active Cursor" button

4- Click on the "Zoom In At Active Cursor"

5- ReAdY !

The following figure details the above steps and the expected result.

Other way

ModelSim offers another way of seeing the delta delay. In the 'View->List' option, the signals and their respective events and delay are detailed in a table. 

The following figure is the respective 'list' of the above case. 

FINALLY

So, if you ever had doubt on how the delta delays works, here is an easy way of find it out !. 

See you soon.... 

Quartus-ModelSim: How to customize the waveforms to facilitate the debug

In a previous blog I described how to customize the waveforms in ModelSim in the Xilinx ISE environment. Due to the request of many of you, I now describe the waveform customization for the Altera Quartus users.  

As you'll read in the application note that I present; when invoking any simulation (functional or gate level) from the Quartus environment, ModelSim is automatically started up, displaying the waveforms resulting from the test bench in the panel called Wave View. Due to the ModelSim's settings (detailed in a script file) by default, only the entity signals are displayed in the waveform viewer, no other signal ... So, once opened this Wave View window if you wish to display internal signals of the design under test, or change the position and / or color of the signals, or add dividers, and many other features offered by ModelSim, you can do it (following certain steps explained later), but once you close ModelSim all modifications are lost!. Hence, when you run the same simulation again, you must start again with the modifications. The problem sound familiar?????

In the 'Application Note' that I present here, I detail the steps to follow, so that when you invoke ModelSim from Quartus, the Wave View will contain all the information you set and saved for proper verification and easy debug.

Here is the link to download the 'Application Note':  AN-08 C7T

Until next time!

ISE-ModelSim: How to Customize the Wave View Window

In case your simulation is executed using ModelSim, when you invoke any kind of simulation within the ISE environment, ModelSim is automatically opened. By default one of the window that comes up is the Wave View window. In this window only the top entity signals are shown, and ... no any other signal ... So if you want to see internal signals of your design, or maybe you want to change the position and/or color of a signal, maybe you want to add dividers,or utilize many other features offered by ModelSim, you can do that in the window that is automatically opened, but. . . any change in the Wave View window will be kept until ModelSim is closed. When running the same simulation again, you should start with the changes that you want once again from scratch.

I've written a kind of application note that describes the necessary steps to follow, so when you invoke ModelSim from ISE, the Wave View will open (keep) any change you have done to the initial (default) window, containing all the information you want/need for proper verification and easy debug:

C7T AN-05

Happy design!