How to get current field polarity of interlaced video output?

[Thomas Hilber]

On Wed, Jul 30, 2008 at 11:01:00PM +0200, Thomas Hilber wrote:
> ah, maybe I now found something:
> 
> register RADEON_CRTC_VLINE_CRNT_VLINE
> 
> alternatively counts from
> 
> 0 - 624    and from
> 0 - 622    the next time.
> 
> probably I can derive the field polarity from this?

Problem fixed! Please find attached a small test program how
to fiddle this.

 Cheers
    Thomas
-------------- next part --------------
#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/mman.h>

#define RADEON_PHYS_BASE 0xeaf00000
#define RADEON_IO_SIZE   0x10000

#define RADEON_CRTC_VLINE_CRNT_VLINE        0x0210
#define RADEON_CRTC_STATUS                  0x005c

#define A(reg) (*(unsigned *)(map_base + (reg)))

/*
 * only works with a modeline like this:
 *
 * Modeline "720x576i" 13.875 720 744 808 888 576 580 585 625 -HSync -Vsync interlace
 *
 * both RADEON_CRTC_VLINE_CRNT_VLINE and RADEON_CRTC_STATUS give the same
 * information about fields. 
 *
 * using RADEON_CRTC_VLINE_CRNT_VLINE you have to wait for
 * transition 622/624 -> 0
 *
 * using RADEON_CRTC_STATUS you can determine the status anytime
 */
main()
{
    int fd;
    int cnt;
    int vline_prev = 0;
    u_char *map_base;

    if ((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) {
        printf("open /dev/mem: %s\n", strerror(errno)); exit(-1);
    }
    map_base = mmap(0, RADEON_IO_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, RADEON_PHYS_BASE);
    if ((int)map_base == -1) {
        printf("mmap hw fails: %s\n", strerror(errno)); exit(-1);
    }
    cnt = 500000;
    while (--cnt) {
    	int vline = A(RADEON_CRTC_VLINE_CRNT_VLINE) >> 16;
	int field = A(RADEON_CRTC_STATUS) >> 3 & 1;

	if (vline < vline_prev) {
	    if (vline_prev == 622 && field) {
		printf("ODD\n");
	    } else if (vline_prev == 624 && !field) {
		printf("EVEN\n");
	    } else {
		printf("inconsistency detected, exiting\n"); exit(1);
	    }
	}
	vline_prev = vline;
    }
}