Re: [sdcc-devel] Please comment on this HOWTO...

[Kim L. <lu...@di...>]

On Wed, 2005-11-23 at 14:03 -0800, Scott Dattalo wrote:
> Kim Lux wrote:
> > Here is a HOWTO I've made to help me and others do a port.  I'd like
> > your comments.  
> 
> <snip>
> 
> Hi Kim,
> 
> I was in the process of replying to the personal request you sent to me 
> when I saw your post. You covered everything I was going to say and then 
> some!

OK.  Thanks. 

> The only thing I can add is a little perspective.

Greatly appreciated...

>  When making the 
> initial changes from whichever port you chose to the xgate port, you'll 
> probably want to apply an invariance coding technique (I just made this 
> term up...). By this I mean attempt to make a literal one-for-one 
> mapping of all common components (e.g. changing MOV instructions to MOVE 
> instructions, or whatever). For things that don't have one-to-one 
> mapping you can still emit the original port's code -or- even better 
> debug statements which can serve as an indicator for the things that 
> need to be changed.

OK. 

> When I did the very first PIC port, I applied this technique and with 
> int a few weeks had some very preliminary code compiling.

Good to know.  I think the hardest part of the exercise will be
allocating the registers.

Question: did you have to make any structural changes to the iCode
production itself ?  Or were all your changes in the target directory
code ? 

>  At the time 
> there were no regression tests for SDCC, so I wrote some of my own (in 
> fact, there still in src/regression bit rotting away...). The regression 
> tests allow you to easily focus on corner cases.

Good to know.  Did you regression cases go in any particular order ?

Can you comment on how you renamed things/ removed things in some
logical order ?  Just search and replace mcs51 with pic and deal with
compile errors or what ? 

> I imagine after about 200 of coding the PIC port was of alpha quality. I 
> spent probably another 200 hours getting a back end optimizer working, 
> but at that point the code was still alpha quality. I have no idea how 
> much time has been spent on the PIC ports now, but I suspect probably 
> more than 1000 hours or more have been invested. 

Yikes. 

> And based on the bug 
> reports I see it appears the PIC port has dramatically improved perhaps 
> to high beta quality.
> 
> Expect to invest some time! And good luck!
> 
> Scott
> 
> 
> 
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-- 
Kim Lux,  Diesel Research Inc.