[TriEmbed] Hacking a fake vintage radio (with Arduino + Pi 0)

Huan Truong htruong at tnhh.net
Tue Jun 30 11:48:12 CDT 2020


Oh yeah, that explains my issue. I definitely ran into that issue
where I have checked and had no reason to believe I was doing
something wrong, yet, when I evacuated each switch to a function, the
switch worked correctly. But neither scoping with an anonymous scope
nor renaming the variables work.

The reason I used the switch was that I read on stackoverflow at one
point and someone said that we should use switches instead of elseifs
when we have a lot of cases. Then, using switches, the compiler will
be able to (at some point) create a lookup table for you so it's
faster. I doubt that was what happening at least on the Arduino case.
You'll need a giant lookup table which the uCs don't have memory for.
I suspect that in a lot of cases, using switches is probably just as
slow as using elseifs. Now as I see that it is so buggy, I probably
will not use switches, at least on Arduino.

Cheers,
- Huan.

On Tue, Jun 30, 2020 at 9:23 AM Brian via TriEmbed
<triembed at triembed.org> wrote:
>
> Side note:
>
> The arduino compiler has bugs in how it handles switch statements.  I've
> run into situations lately where the order of the case statements matter
> (which it never should); cases are completely ignored, etc.
>
> I believe it may be tied to the use of local scoping within a case, e.g.:
>
> switch(thing) {
>     case 1:
>        {
>           // stuff with case-local scope
>        }
>        break;
> }
>
> Syntactically- and semantically-correct code has proven to generate
> incorrect runtime results.
>
> I haven't had time/motivation to submit a bug report, but I should do
> that.  At any rate, a potential workaround is to reorder your cases.
>
> -B
>
> On 6/24/20 9:51 PM, Huan Truong via TriEmbed wrote:
> > Thanks Pete!
> >
> > I feel like there was something really mysterious about the switch statement. Even if I pasted the whole blocks of code of each function I would have called to the {} inside a case, the code still wouldn’t work. That baffled me by a mile.
> >
> > But yeah, I spent way too much time on the project that I’m comfortable with the idea of not understanding some of it now. The watchdog timer code was baffling too.
> >
> > Please excuse my typos, sent from phone.
> >
> > On Jun 24, 2020, at 10:14 AM, Pete Soper via TriEmbed <triembed at triembed.org> wrote:
> >
> > What a beautifully presented adventure. Loved reading it. And when you say a problem "could be bad" you make your point. :-) (meant as a "find Waldo" exercise for alert readers)
> >
> > Hadn't heard of "kev" or any other Arduino emulator for that matter. That aspect was interesting too.
> >
> > The other issue with redeclaration of the vars local to the switch statement is that they literally don't exist outside it, so communicating their values outside the block would be difficult. :-)  In general, every {} defines a local scope in C/C++ and you can declare variables inside that scope but they cease to be defined outside the scope. The scope outside any {} (aka "global") or vars declared "static" can avoid this issue but not the redefine issue.
> >
> > Thanks for sharing this!
> >
> > Pete
> >
> >
> >> On 6/24/20 12:43 PM, Huan Truong via TriEmbed wrote:
> >> This has taken me way more time than I thought, but finishing this
> >> retrofit is a big achievement for me. It's really silly and serves
> >> exactly no purpose other than RE'ing something no one cares about.  So
> >> I just want to share for some shits and giggles.
> >>
> >> http://www.tnhh.net/posts/adventures-hacking-fake-vivitar-vintage-radio.html
> >>
> >>
> >>
> >>
> >>
> >
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-- 

Huan Truong
www tnhh.net / twitter @huant



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