Re: printf not working, if buffering disabled

[Jeff Johnston <jjohnstn at redhat dot com>]

On 09/18/2011 08:13 AM, Marc Donner wrote:
> Hi,
>
> i've wrote a small program using newlib's printf funktion. All works
> well as long as buffering is enabled. If I disable buffering using the
> following code
>
> setvbuf(stdout, NULL, _IONBF, 0);
>
> the printf functions are not working anymore, while a call to putchar
> produces the expected result.
>
> The code looks like this
>
> #include<stdio.h>
>
> void
> main (void) {
> 	/* init USB CDC device */
> 	usbcdc_init();
>
> 	//setvbuf(stdout, NULL, _IONBF, 0);
> 	putchar('y');
> 	putchar('\n');
> 	iprintf("test\n"); /*<- not working if buffering disabled */
>
> 	while (1);
> }
>
> The _write syscall is implemented as
>
> int _write(int file, char *ptr, int len) {
> 	while (len--) {
> 		if (*ptr == '\n') {
> 			usbcdc_putch('\r');
> 		}
> 	}
> 	return len;
> }
>
> Anybody an idea?

Marc,

Your test case works fine on a mn10300 simulator using newlib so I would 
tend to suspect there is something wrong with your implementation.

If that is actually the code for _write, it has multiple flaws.  It 
doesn't move ptr forward and doesn't appear to write any characters to 
the system but '\r'.  It also returns -1 instead of number of bytes 
written.  I hope you are just summarizing your code, otherwise, there's 
no way this could work.  I'm guessing you have probably mapped putchar 
to usbcdc_putch somewhere.

Test out your write syscall by calling it directly instead of iprintf. 
If your _write works, try debugging and follow the iprintf down to 
__sfvwrite_r and then fp->_write, etc...   If you can't use a debugger 
for your platform, you might need to add appropriate usbcdc_xxxx 
statements so you can track your progress.

-- Jeff J.

> Regards,
>
> Marc