Hi Community,

I am having a problem that I cannot understand.

This simulation uses wreal only.

I have 2 internal signals which should react to a variation in the signal iload.

If iload > value the response signal should be high, otherwise the response signal should be low.

Example 1 (working as expected)
I am varying iload in steps of 1m.
Let's say value=100m
If iload  is 100m or higher, then the response signal should be high
If iload is 99m or lower then the response signal should be low
-> this is working fine


The problem occurs if I use another "value", let's say value=50m

Example 2 (not working as expected)
I am varying iload in steps of 1m.
Let's say value=50m
If iload  is 50m or higher, then the response signal should be high
If iload is 49m or lower then the response signal should be low
-> this is not working fine. When iload decreases the response signal should become low when iload=49m, but this is ocurring when iload=50m and this is not correct


This is the code that I am using:

     real        high_current_overload;
     real      low_current_overload;
     
     always @(iload) begin
     
           if (iload >= 100m) begin
                 high_current_overload = 1.0;
           end else begin
                 high_current_overload = 0.0;
           end
     
     end      
     
     always @(iload) begin
     
           if (iload >= 50m) begin
                 low_current_overload = 1.0;
           end else begin
                 low_current_overload = 0.0;
           end
     
     end      
     
See Picture 1.

Please any suggestion to understand what is causing this problem?      

Thank you!

Zorro.

Zorro wrote on Sep 17^th, 2015, 5:41am:
Accumulation of numerical errors. I am sure your code will behave as expected if you use 49.995m as threshold.
- B O E

Picture 2.

Zorro wrote on Sep 17^th, 2015, 10:59am:
Zorro,
the simulator (usually) uses a binary representation for numbers, and the binary representation of 1m is infinite. Therefore, numerical errors occur and propagate through your calculation.
You may want to try the following (pseudo-)code
Code:

sum = 0
for i = 1 to 10000
   sum = sum + 1m
   print i, ": ", sum - 0.001*i 

- B O E