Re: [Qemu-devel] [PATCH] Timer/clock for Linux

[NyOS <lista@nyos.homelinux.net>]

On Mon, 24 Apr 2006 23:41:23 +0200, Fabrice Bellard <fabrice@bellard.org>  
wrote:

> Hi,
>
> Can other people confirm that it is better to always use /dev/rtc on  
> Linux ? Is there a way to get the real resolution of the host timer ?
>
> Fabrice.

Hi!

There must be one.
Mplayer says this after setting /proc/sys/dev/rtc/max-user-freq below 1024:

Linux RTC init error in ioctl (rtc_irqp_set 1024): Permission denied
Try adding "echo 1024 > /proc/sys/dev/rtc/max-user-freq" to your system  
startup scripts.
Using nanosleep() timing

URL=http://mplayerhq.hu/homepage/design7/dload.html

this code can be found in mplayer.c file aprox. 1100th line:

#ifdef HAVE_RTC
   if(!nortc)
   {
     // seteuid(0); /* Can't hurt to try to get root here */
     if ((rtc_fd = open(rtc_device ? rtc_device : "/dev/rtc", O_RDONLY)) <  
0)
	mp_msg(MSGT_CPLAYER, MSGL_WARN, "Failed to open %s: %s (it should be  
readable by the user.)\n",
	    rtc_device ? rtc_device : "/dev/rtc", strerror(errno));
      else {
	unsigned long irqp = 1024; /* 512 seemed OK. 128 is jerky. */

	if (ioctl(rtc_fd, RTC_IRQP_SET, irqp) < 0) {
     	    mp_msg(MSGT_CPLAYER, MSGL_WARN, "Linux RTC init error in ioctl  
(rtc_irqp_set %lu): %s\n", irqp, strerror(errno));
	    mp_msg(MSGT_CPLAYER, MSGL_HINT, "Try adding \"echo %lu >  
/proc/sys/dev/rtc/max-user-freq\" to your system startup scripts.\n",  
irqp);
    	    close (rtc_fd);
     	    rtc_fd = -1;
	} else if (ioctl(rtc_fd, RTC_PIE_ON, 0) < 0) {
	    /* variable only by the root */
     	    mp_msg(MSGT_CPLAYER, MSGL_ERR, "Linux RTC init error in ioctl  
(rtc_pie_on): %s\n", strerror(errno));
     	    close (rtc_fd);
	    rtc_fd = -1;
	} else
	    mp_msg(MSGT_CPLAYER, MSGL_INFO, MSGTR_UsingRTCTiming, irqp);
     }
   }

I've never used RTC in my programs, but ioctl seems to return negative  
value on such an error. A hint like that can also be good on startup.

Miklos Gyozo (Nyos)