ColdFire/68K Microcontrollers and ProcessorsのトピックRe: Newbie question

Newbie question

gbaars — Thu, 03 Jul 2008 02:29:59 GMT

In a first try on the DEMOJM with MCF51JM128

(blinking a led) the watch dog is disabled.

Before blinking loop the line

MCGC2 = MCGC2 && 0b11111111;

seems to double the busfreq (why effect at all?)??

Re: Newbie question

JimDon — Thu, 03 Jul 2008 02:36:25 GMT

Because && resolves to true or false.

Did you mean '&'?

Re: Newbie question

gbaars — Thu, 03 Jul 2008 03:15:33 GMT

MCGC2 = MCGC2 & 0b11111111;

does not compile (int to unsigned char conversion error).

Re: Newbie question

RichTestardi — Thu, 03 Jul 2008 08:02:22 GMT

Hi,

> MCGC2 = MCGC2 & 0b11111111;
>
> does not compile (int to unsigned char conversion error).

Arithmetic operators produce integer results by default, and an implicit cast from an integer to an unsigned char produces a warning/error by default.

You might try an unsigned char operator:

MCGC2 &= 0b11111111;

Or an explicit cast:

MCGC2 = (unsigned char)(MCGC2 & 0b11111111);

Or just disable the error/warning:

turn off "Implicit Arithmetic Conversions" in project settings -> C/C++ Warnings

I actually run with that error/warning disabled.

-- Rich

Re: Newbie question

gbaars — Thu, 03 Jul 2008 16:25:42 GMT

Works fine.

Re: Newbie question

JimDon — Thu, 03 Jul 2008 22:24:33 GMT

Well, some would recommend that you not turn off warnings, and that you explicitly cast to eliminate the warnings.

If fact, if you need to comply with a standard, like MIRSA, you are not permitted to turn warnings off.

Although it may seem warnings are just an annoyance, sometimes they do point to a problem.
I have used pragmas to disable certain warnings for a small block of code, but never disable them completely.
Also, if you work professionally, you may be required to leave them on, so you should learn about them.

Code that compiles clean with warnings off is not code that really is clean, and if you decide later to turn them back on you will have a big job to go fix them all.