Re: [Iverilog-devel] running iverilog and vvp from the build tree (no make install)

[Martin W. <ic...@ma...>]

Galen Seitz wrote:
> On 8/9/19 1:16 PM, Martin Whitaker wrote:
>> Martin Whitaker wrote:
>>> On 09/08/19 10:11, Evan Lavelle wrote:
>>>> On 09/08/2019 01:28, Galen Seitz wrote:
>>>>> Hello again,
>>>>>
>>>>> In order to track down the commit that caused the behavior change 
>>>>> between 0.9 and 0.10 that is being discussed in another thread,
>>>>
>>>> I wouldn't bother. If Martin's right (and I'm sure he is) then this is 
>>>> a 'feature' in the Lattice model, and whether or not Q initialises 
>>>> correctly is just a roll of the dice (but probably deterministic for a 
>>>> given simulator). You may be able to find a switch on one of the other 
>>>> simulators to randomise the initialisation order, which would be 
>>>> interesting - you should find that Q resets on some runs but not on 
>>>> others (Steve wanted to do this for Icarus, but I don't think it ever 
>>>> happened).
>>>>
>>>> This is exactly what SV's 'always_comb' is meant to fix. This was a 
>>>> very late attempt to rationalise simulation start-up in Verilog (to, 
>>>> curiously, exactly what VHDL had done since day #1).
>>>
>>> And indeed, replacing the "always @ QB" with "always_comb" fixes the 
>>> problem.
>>>
>>> However, Icarus tries to protect the user against such problems by 
>>> preferentially scheduling "always" processes ahead of "initial" 
>>> processes at time 0. The reason it is not working in this case is that 
>>> the initial process in a UDP is handled differently to normal initial 
>>> processes, and in v10 and later is being scheduled ahead of the "always" 
>>> processes. Although this is legal behaviour, I will look at changing it 
>>> to restore the more user-friendly behaviour of v0.9.
>>
>> I've pushed the change to both the master and v10 branches.
> 
> Thanks, I'll give it a try.
> 
> Regarding the question in the subject line, do you have a preferred way of 
> running iverilog and vvp when you are working on the Icarus code?
> 
I always run 'make install'. If you don't want to affect your working 
installation, run configure with the --prefix option to set the 
installation root to someplace else, or with the --suffix option to make 
the filenames unique. If you want to keep multiple builds for comparison, 
you can build out-of-tree.