[SOLVED] I am getting mad with with AVR-GCC . Why while(p) {data(p++);} not working?

vinodstanur · Feb 19, 2012

I am new to avr-gcc.
I am just trying an lcd program for atmega16.

Now,

data('H'); data('E'); data('L'); data('L'); data('O');

The above code is working fine!!!

But...
below code is not

const char *p = "HELLO";
while(*p) data(*p++);

below code is also not working,
char *p = "HELLO";
while(*p) data(*p++);

But the below code is WORKING!!
const char *p = "HELLO";
data(*p++);
data(*p++);
data(*p++);
data(*p++);
data(*p++);

!!!!!

Why ???????

alexan_e · Feb 19, 2012

p is a pointer and p++ increments the pointer address , how do you expect to get the value pointed by p without using the * (as you do in data(p++))

---------- Post added at 23:48 ---------- Previous post was at 23:42 ----------

c = *p++; // assign to c the value pointed by p, and then increment the address p
c = *++p; // increment the address p, then assign c the value pointed to by p
c = ++*p; // increment the value pointed to by p,then assign it to c, leaving the address of p untouched
c = (*p)++ // assign c the value pointed to by p, then increment the value pointed to by p leaving the address of p untouched

vinodstanur · Feb 19, 2012

Sir it was a typing mistake..
I really mean data(*p++) is also not working!!!!!!!!

I tried a lot...

my function
void string(const char *p) {
data(*p++);
}

is not working!!!!

if I call it with
string("HELLO WORLD");

it seems strange ...

alexan_e · Feb 19, 2012

I'm not very clear on the problem, I don't understand what you are trying to do.

Post your string function and the way you call it.
Does string("HELLO WORLD"); work or not?

this while(*p) data(*p++); works fine for me.

vinodstanur · Feb 19, 2012

My complete code:

Code:

#include<avr/io.h>
#define F_CPU 12e6
#include <util/delay.h>
#define RS 6 //PD6
#define EN 7 //PD7
#define databits PORTC

void port_init()
{
    DDRC = 0xff;
   	DDRD = (1 << RS)|(1 << EN);
}

void LCD_STROBE(void)
{
    PORTD |= (1 << EN);
    _delay_us(1);
    PORTD &= ~(1 << EN);
}

void data(unsigned char c)
{
    PORTD |= (1 << RS);
    _delay_us(50);
    databits = (c >> 4);
    LCD_STROBE();
    databits = (c);
    LCD_STROBE();
}

void cmd(unsigned char c)
{
   	PORTD &= ~(1 << RS);
    _delay_us(50);
    databits = (c >> 4);
    LCD_STROBE();
    databits = (c);
    LCD_STROBE();
}

void clear(void)
{
    cmd(0x01);
    _delay_ms(5);
}

void lcd_init()
{
    _delay_ms(15);
    cmd(0x38);
    _delay_ms(1);
    cmd(0x38);
    _delay_us(100);
    cmd(0x38);
    cmd(0x28);			// Function set (4-bit interface, 2 lines, 5*7Pixels)
    cmd(0x28);			// Function set (4-bit interface, 2 lines, 5*7Pixels)
    cmd(0x0c);			// Make cursorinvisible
    clear();			// Clear screen 
    cmd(0x6);			// Set entry Mode(auto increment of cursor)
}

void string(const char *q)
{
while(*q)
	data(*q++);
}

int main()
{
    _delay_ms(50);
    port_init();
    lcd_init();
    cmd(0x80);
	data('H');
	_delay_ms(1000); //to cofirm H is printed on LCD (Working fine)
	string("HELLO WORLD"); //NOT WORKING FOR ME :-( DONT KNOW WHY!!
	while(1);
	return 0;
}

command line I used:

Code:

avr-gcc -mmcu=atmega16 -Os lcd.c
avr-objcopy -j .text -O ihex a.out a.hex

---------- Post added at 23:28 ---------- Previous post was at 23:24 ----------

If some one could compile it using avr-gcc and provide the hex, then I could confirm if it is some thing wrong with my packge or not,,,

alexan_e · Feb 19, 2012

This is the compiled hex View attachment m16.zip

You don't have a loop inside string

Code:

void string(const char *q)
{
   while (*q)  data(*q++);
}

Was that what you tried and wasn't working?

FvM · Feb 19, 2012

this while(*p) data(*p++); works fine for me

Do you mean with AVR-GCC?

I guess the problem is related to the necessity to generate LPM instructions for const data located in Flash memory. The *p++ syntax is generally O.K., but it's not working for Flash memory without special compiler prerequisites. But I'm not familiar with AVR-GCC and don't know how they are solving this problems. You should find informations about handling of flash memory pointers in the documentation.

When facing problems like this, I would generally inspect the generated assembly code to understand why it's not working. Or use a hardware debugger or possibly a simulator.

P.S.: Sounds like a more trivial problem. But then the observations in post #1 aren't fully correct?

You don't have a loop inside string

vinodstanur · Feb 19, 2012

alexan_e said:
This is the compiled hex View attachment 69422

You don't have a loop inside string

Code:

void string(const char *q) { while (*q) data(*q++); }

Was that what you tried and wasn't working?

AM AGAIN SORRY...IT WAS ALSO A TYPING MISTAKE....pls don't mind

alexan_e · Feb 19, 2012

Yes I meant AVR-GCC.
He is not using flash memory data, the const data is still in RAM memory but can't be changed.
In order to use flash he needs to include #include <avr/pgmspace.h> and use the PROGMEM

https://www.avrfreaks.net/index.php...ic&t=38003&start=all&postdays=0&postorder=asc

---------- Post added at 00:40 ---------- Previous post was at 00:38 ----------

vinodstanur said:
AM AGAIN SORRY...IT WAS ALSO A TYPING MISTAKE....pls don't mind

Should I recompile it using the string function with the while (*q) addition?

vinodstanur · Feb 19, 2012

alexan_e said:
Yes I meant AVR-GCC.
He is not using flash memory data, the const data is still in RAM memory but can't be changed.
In order to use flash he needs to include #include <avr/pgmspace.h> and use the PROGMEM

https://www.avrfreaks.net/index.php...ic&t=38003&start=all&postdays=0&postorder=asc

---------- Post added at 00:40 ---------- Previous post was at 00:38 ----------

Should I recompile it using the string function with the while (*q) addition?

Yes Sir,
I would be happy if you could ones again compile it with while(*p)

alexan_e · Feb 19, 2012

This is the compiled hex of the code posted is message #5 View attachment m16v2.zip
The previous hex was from the code you have send using PM which was missing the while loop

vinodstanur · Feb 19, 2012

Oh!!!!!!! IT IS WORKING!!!!!
So what may be wrong with my avr-gcc?!!

alexan_e · Feb 19, 2012

I can't imagine there is something wrong with your gcc, since you said that data('H'); worked fine but you only had problem to print a string.
Try to recompile with the while inside the string function.

Are you using winAVR as standalone or with AVRstudio?

---------- Post added at 00:58 ---------- Previous post was at 00:55 ----------

I'm using AVRstudio v4.18 with winavr20090313

FvM · Feb 19, 2012

the const data is still in RAM memory

Then there's absolutely no reason why it shouldn't work.

vinodstanur · Feb 19, 2012

alexan_e said:
I can't imagine there is something wrong with your gcc, since you said that data('H'); worked fine but you only had problem to print a string.
Try to recompile with the while inside the string function.

Are you using winAVR as standalone or with AVRstudio?

---------- Post added at 00:58 ---------- Previous post was at 00:55 ----------

I'm using AVRstudio v4.18 with winavr20090313

I really don't know WinAVR or avrstudio. Am new to avr..
Now using avr-gcc and the command line which I posted in previous post,,,
Here is a screenshot of terminal...

vinodstanur · Feb 19, 2012

char *p = "HELLO";
data(*p++);data(*p++);data(*p++);data(*p++);data(*p++);

Above sample is WORKING FINE!!

Now it is becoming hard to find what is the exact problem...
At present, it seems some thing like,
inside while condition, *p is not possible..
(in my case)

Because I checked below code:

char *p = "HELLO";
while(*p) {data('A'); p++};
this is printing more that 5 'A' ...
exactly more than 32 As, since I could observe lcd is filled with letter A,,.

alexan_e · Feb 19, 2012

Have you recompiled it making sure that you use

Code:

void string(const char *q)
{
   while (*q)  data(*q++);
}

You are using a linux OS, I have never used any AVR tool-chain in a linux environment so I have no idea about it

Avrstudio can be download from Atmel but it is intended for windows.

---------- Post added at 01:29 ---------- Previous post was at 01:27 ----------

vinodstanur said:
char *p = "HELLO";
data(*p++);data(*p++);data(*p++);data(*p++);data(*p++);

Above sample is WORKING FINE!!

Now it is becoming hard to find what is the exact problem...
At present, it seems some thing like,
inside while condition, *p is not possible..
(in my case)

Because I checked below code:

char *p = "HELLO";
while(*p) {data('A'); p++};
this is printing more that 5 'A' ...
exactly more than 32 As, since I could observe lcd is filled with letter A,,.

Use a null terminated string, while(*p) will continue until it finds a null character

vinodstanur · Feb 19, 2012

Yes I have recompiled it with while(*p)...

still not working...
lcd is showing many symbols and all...Entire screen...

but this is printing zero in LCD...

char *p = "HELLO";
data(*(p + 5) + '0');

Above code is printing NUMBER 0 in lcd...So it confirms that the string is terminating with null!!

bigdogguru · Feb 19, 2012

If you would like an IDE compatible with both Linux and AVR-GCC.

You might want to take a look at Code::Blocks.

BigDog

vinodstanur · Feb 19, 2012

But is there a chance for such a bug in avr-gcc since it is much popular already...

I wan;t to find some one who already have avr-gcc in their system to compile it for me...Then only I could confirm what is wrong..

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[SOLVED] I am getting mad with with AVR-GCC . Why while(*p) {data(*p++);} not working?

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[SOLVED] I am getting mad with with AVR-GCC . Why while(p) {data(p++);} not working?