Bug in Imagecraft AVR?

Seems the type 'char' is unsigned, isn't it?

Vadim

I've always mistrusted the 'break' function---seems too much like BASIC to me! i would code the function more like:

#define MAXFIELD 5 for (i=0;i 0) { do something.... } }

About the only only place I use 'break' is after the case elments in a switch statement.

It would be interesting to see what assembly language is being generated by your compiler for this code. Perhaps there is an obvious error in the generated object code.

Mark Borgerson

Another thought: Is it possible that get_data_field is returning zero?

Mark Borgerson

No. char is signed.

Meindert

What happens for r==0?

No. Plain char, signed char, and unsigned char are three distinct types. It is implementation-defined as to whether plain char is signed or not. Most 8-bit compilers I'm familiar with make it unsigned by default.

If you want a small int, use signed char. Typedef it if the name bugs you. I use S8 or SI8

Never use plain char for anything. It's useless, even dangerous. Particularly unsuitable for character data.

Regards,

-=Dave

Yes, sometimes. But I found the culprit (with apologies to Vladimir): a char type in unsigned in ICC AVR. So I have to explicitly declare 'signed char get_data_field()' So now it works OK.

Meindert

It's time for some old-fashioned debugging. You are assuming that char is signed, which may be true for your compiler, but needn't be for C in general (it is good practice to type the variable signed char, which will force it to be signed on any conforming compiler). What is the return type for get_data_field()? If it is int and the return value is outside the range of r, you could get a false indication.

I suggest looking at the generated code. You may be able to have the compiler generate assembly output or you can look at disassembled code. In either case, verify the code for the first test on r.

It may be that the value returned in r isn't what you think it is. You can use a simulator, ICE, or other means to inspect the returned data. For debugging realtime applications on the fly I have inserted code to generate pulse patterns on a spare pin at certain critical points in the code.

Thad

And so I have noticed :-(....

When I write in C builder, char is always signed. In my older versions of '51 compiler, it was signed. Even in my Z80 compiler. Sigh..... Thanks for the hint though.

Meindert

I'd use a loop that allows me to do checks, eg a while loop.

You're aware that imagecraft have their own list servers to answer questions related to the ICCAVR ? Available at the imagecraft website.

Rene

... Yes, I am still here :-) and yes, the problem is that "char" is unsigned.

-- // richard

No, the problem is the programmer _assumed_ it was signed.

-- Grant Edwards grante Yow! Where's th' DAFFY at DUCK EXHIBIT?? visi.com

"Meindert Sprang" wrote in news: snipped-for-privacy@news.nb.nu:

Although the folks in comp.lang.c don't approve of this, I find it has saved me many a time in my embedded work with C compilers. Once I include this file I never use C's char, int, short, etc., only these base types.

#ifndef fixed_types_h_included #define fixed_types_h_included

/* fixed_types.h

#endif /* fixed_types_h_included */

HTH.

Well, it does not make much difference which loop you use. Even the for loop does a check. Instead of usgin the obvious

for (i=0;i You're aware that imagecraft have their own list servers to answer questions

Didn't know that. I'll take a look there. Thanks.

Meindert

Hi Richard,

Yes, I have noticed it. And read it in the help file when I specifically looked for it. Thanks.

Meindert

unsigned.

Yes. But it was an assumption based on experience. All compilers I have previously used treated char as signed unless an option was set. But you learn something everyday :-)

Meindert

Here's my usage, which I recommend:

signed char for 8-bit (or more) signed values unsigned char for 8-bit (or more) unsigned values char for actual characters.

This is portable to any conforming C compiler.

Thad

I thought the same but I just looked in K&R and they specifically state that the sign of char is _not_ defined.

Actually I always do a typedef of unsigned char to byte which seems much more sensible to me for an embedded system.

Mike Harding

They're the worst kind, because you don't much think about them.

I've decided it's time to start using the C99 standard names when I want to specify exactly how many bits to use:

If your compiler doesn't suppor them via stdint.h, you can certainly make your own typedefs.

And here's a clever hack from

static union { char int8_t_incorrect[sizeof( int8_t) == 1]; char uint8_t_incorrect[sizeof( uint8_t) == 1]; char int16_t_incorrect[sizeof( int16_t) == 2]; char uint16_t_incorrect[sizeof(uint16_t) == 2]; char int32_t_incorrect[sizeof( int32_t) == 4]; char uint32_t_incorrect[sizeof(uint32_t) == 4]; };

From a practical standpoint, I would suggest using unsigned char for "actual" characters. In all cases, the char value of a member of the execution character set cast to unsigned char will have the same representation (and vice-versa), so there's no real downside, even for standard library functions expecting char or char*. And it prevents errors like the following:

A number of years ago, I had a system with a custom terminal for the user interface. The terminal had a set of function keys, and would return 0xF1 for F1, 0xF2 for F2, etc. I learned the hard way that the following is an infinite loop if char is signed (functions simplified for the sake of the example):

#define EXIT_KEY 0xF1 char get_key(void){return EXIT_KEY;} void process(char k){printf("key is %02x\n",k);}

char key; do{ key = get_key(); process(key); } while (key != EXIT_KEY);

The example might be familiar to some of you. I've posted it before. Several times. ;-)

Regards,

-=Dave