Page 1 of 1
Trying to get a string printed on screen
Posted: Fri Mar 20, 2009 3:45 am
by bazi
Hi,
i'v done the bare bones tutorial and now i'm trying go write a small lib for i/o. Actually i'm on the functions for printing on screen.
I've done a function for printing a char on the screen, located 1 after the last char (code for this is attached after my post).
Now i'll try to write a function for printing a whole string instead of only on character, but it prints nothin....
Here's the code, which isn't working.
Code: Select all
void print(char str[]);
.....
print("hi");
.....
void print(char str[]) {
unsigned int count=0;
while(str[count] != 0) {
printc(str[count]);
count++;
}
}
This is the code for only one character, it's working:
Code: Select all
void printc(unsigned char c) {
unsigned char *videoram = (unsigned char *) 0xB8000;
unsigned char *video_mode = (unsigned char *) 0x500;
unsigned char x = video_mode[0];
unsigned char y = video_mode[1];
unsigned char color = video_mode[2];
int pos_char = (x*2)+(y*160);
videoram[pos_char] = c;
videoram[pos_char+1] = color;
x++;
if(x == 80) {
x = 0;
y++;
}
if(y == 25) {
y = 0;
}
video_mode[0] = x;
video_mode[1] = y;
set_cursor(x, y);
}
Re: Trying to get a string printed on screen
Posted: Fri Mar 20, 2009 3:52 am
by AJ
Hi,
Are you currently using a linker script and if so, do you explicitly place the .data and .rodata sections? If not, that's the first thing you need to look at.
I must say - the prototype for the print function looks...unusual too. Are you really able to compile that code with no warnings - at least about implicit conversion of a const char* to a char*? I'll take your word for it that the printc function is working.
Cheers,
Adam
Re: Trying to get a string printed on screen
Posted: Fri Mar 20, 2009 4:02 am
by jal
bazi wrote:void print(char str[])
Could you please change that to "void print(char* str)" and try again? Iirc, using [] in parameter lists doesn't always work well.
JAL
Re: Trying to get a string printed on screen
Posted: Fri Mar 20, 2009 4:04 am
by bazi
I'm compiling with gcc with -Wall, no warnings.
A Part of my linker script:
Code: Select all
.rodata ALIGN (0x1000) : {
*(.rodata)
}
.data ALIGN (0x1000) : {
*(.data)
}
I'll take your word for it that the printc function is working.
Yes, it's working
I wrote the function of printing on char within print(), but this didn't work...
Could you please change that to "void print(char* str)" and try again? Iirc, using [] in parameter lists doesn't always work well.
Ok, i'll try it
//Edit: hmmmm char* str doesn't work too... Would it help, if i post more source code? But there is not much more.... only a main file, bootloader (taken from the bare bones tutorial) and functions like clr_scr() and printc() ....
Re: Trying to get a string printed on screen
Posted: Fri Mar 20, 2009 4:49 am
by bazi
Now i'm confused.... I got it working, but not the way i want to.
With this print()
Code: Select all
void print(char str[]) {
unsigned int count=0;
while(str[count] != 0) {
printc(str[count]);
count++;
}
}
and this code:
But print("hallo"); isn't working...
Re: Trying to get a string printed on screen
Posted: Fri Mar 20, 2009 5:17 am
by AJ
Hmmm - this really sounds like a .rodata problem. I guess with the barebones you are using GRUB and therefore the section is being loaded properly?
The one other thing I can think of is a stack-based parameter passing problem. Are you happy that you have a reasonable sized stack that is stored away from the rest of your code?
Cheers,
Adam
Re: Trying to get a string printed on screen
Posted: Sat Mar 21, 2009 9:57 am
by bazi
ouh, it was a really stupid mistake...
I've exported CC and AS for easier use in Makefiles. But the bins were /usr/bin/gcc-linux-.... instead of /usr/cross-....
This was caused by copy&paste from a existing Makefile from another project...
I can't say why the other compiler didn't work correctly, but i can say that it did'nt
Now this problem is solved
Thanks a lot guys!