diff --git a/software/videomixer/dvisamplerX.c b/software/videomixer/dvisamplerX.c
index 01f7e029c..cf2a50f7b 100644
--- a/software/videomixer/dvisamplerX.c
+++ b/software/videomixer/dvisamplerX.c
@@ -7,12 +7,13 @@
 #include <hw/flags.h>
 
 #include "time.h"
+#include "fb.h"
 #include "dvisamplerX.h"
 
 #define FRAMEBUFFER_COUNT 4
 #define FRAMEBUFFER_MASK (FRAMEBUFFER_COUNT - 1)
 
-static unsigned int dvisamplerX_framebuffers[FRAMEBUFFER_COUNT][640*480] __attribute__((aligned(16)));
+static unsigned int dvisamplerX_framebuffers[FRAMEBUFFER_COUNT][800*600] __attribute__((aligned(16)));
 static int dvisamplerX_fb_slot_indexes[2];
 static int dvisamplerX_next_fb_index;
 
@@ -49,7 +50,7 @@ void dvisamplerX_init_video(void)
 	mask |= 1 << DVISAMPLERX_INTERRUPT;
 	irq_setmask(mask);
 
-	dvisamplerX_dma_frame_size_write(sizeof(dvisamplerX_framebuffers[0]));
+	dvisamplerX_dma_frame_size_write(fb_hres*fb_vres*4);
 	dvisamplerX_fb_slot_indexes[0] = 0;
 	dvisamplerX_dma_slot0_address_write((unsigned int)dvisamplerX_framebuffers[0]);
 	dvisamplerX_dma_slot0_status_write(DVISAMPLER_SLOT_LOADED);
diff --git a/software/videomixer/fb.c b/software/videomixer/fb.c
new file mode 100644
index 000000000..58b90bcae
--- /dev/null
+++ b/software/videomixer/fb.c
@@ -0,0 +1,103 @@
+#include <stdio.h>
+
+#include <hw/csr.h>
+#include <hw/flags.h>
+
+#include "fb.h"
+
+int fb_hres = 640;
+int fb_vres = 480;
+
+static void fb_clkgen_write(int cmd, int data)
+{
+	int word;
+
+	word = (data << 2) | cmd;
+	crg_cmd_data_write(word);
+	crg_send_cmd_data_write(1);
+	while(crg_status_read() & CLKGEN_STATUS_BUSY);
+}
+
+void fb_set_mode(int mode)
+{
+	int clock_m, clock_d;
+
+	switch(mode) {
+		default:
+		case FB_MODE_640_480: // Pixel clock: 25MHz
+			fb_hres = 640;
+			fb_vres = 480;
+			clock_m = 2;
+			clock_d = 4;
+			fb_fi_hres_write(640);
+			fb_fi_hsync_start_write(656);
+			fb_fi_hsync_end_write(752);
+			fb_fi_hscan_write(800);
+			fb_fi_vres_write(480);
+			fb_fi_vsync_start_write(492);
+			fb_fi_vsync_end_write(494);
+			fb_fi_vscan_write(525);
+			break;
+		case FB_MODE_800_600: // Pixel clock: 50MHz
+			fb_hres = 800;
+			fb_vres = 600;
+			clock_m = 2;
+			clock_d = 2;
+			fb_fi_hres_write(800);
+			fb_fi_hsync_start_write(848);
+			fb_fi_hsync_end_write(976);
+			fb_fi_hscan_write(1040);
+			fb_fi_vres_write(600);
+			fb_fi_vsync_start_write(636);
+			fb_fi_vsync_end_write(642);
+			fb_fi_vscan_write(665);
+			break;
+		case FB_MODE_1024_768: // Pixel clock: 65MHz
+			fb_hres = 1024;
+			fb_vres = 768;
+			clock_m = 13;
+			clock_d = 10;
+			fb_fi_hres_write(1024);
+			fb_fi_hsync_start_write(1048);
+			fb_fi_hsync_end_write(1184);
+			fb_fi_hscan_write(1344);
+			fb_fi_vres_write(768);
+			fb_fi_vsync_start_write(772);
+			fb_fi_vsync_end_write(778);
+			fb_fi_vscan_write(807);
+			break;
+		case FB_MODE_1920_1080: // Pixel clock: 148MHz
+			fb_hres = 1920;
+			fb_vres = 1080;
+			clock_m = 74;
+			clock_d = 25;
+			fb_fi_hres_write(1920);
+			fb_fi_hsync_start_write(2008);
+			fb_fi_hsync_end_write(2052);
+			fb_fi_hscan_write(2200);
+			fb_fi_vres_write(1080);
+			fb_fi_vsync_start_write(1084);
+			fb_fi_vsync_end_write(1089);
+			fb_fi_vscan_write(1125);
+			break;
+	}
+	fb_dma0_length_write(fb_hres*fb_vres*4);
+	fb_dma1_length_write(fb_hres*fb_vres*4);
+
+	fb_clkgen_write(0x1, clock_d-1);
+	fb_clkgen_write(0x3, clock_m-1);
+	crg_send_go_write(1);
+	printf("waiting for PROGDONE...");
+	while(!(crg_status_read() & CLKGEN_STATUS_PROGDONE));
+	printf("ok\n");
+	printf("waiting for LOCKED...");
+	while(!(crg_status_read() & CLKGEN_STATUS_LOCKED));
+	printf("ok\n");
+
+	printf("VGA: mode set to %dx%d\n", fb_hres, fb_vres);
+}
+
+void fb_enable(int en)
+{
+	fb_enable_write(!!en);
+}
diff --git a/software/videomixer/fb.h b/software/videomixer/fb.h
new file mode 100644
index 000000000..7b9cc926c
--- /dev/null
+++ b/software/videomixer/fb.h
@@ -0,0 +1,16 @@
+#ifndef __FB_H
+#define __FB_H
+
+enum {
+    FB_MODE_640_480,
+    FB_MODE_800_600,
+    FB_MODE_1024_768,
+    FB_MODE_1920_1080
+};
+
+extern int fb_hres, fb_vres;
+
+void fb_set_mode(int mode);
+void fb_enable(int en);
+
+#endif /* __FB_H */
diff --git a/software/videomixer/main.c b/software/videomixer/main.c
index aa92c0f87..4a44be7df 100644
--- a/software/videomixer/main.c
+++ b/software/videomixer/main.c
@@ -8,6 +8,7 @@
 #include <console.h>
 
 #include "time.h"
+#include "fb.h"
 #include "dvisampler0.h"
 #include "dvisampler1.h"
 
@@ -80,10 +81,10 @@ static void fb_service(void)
 	if(readchar_nonblock()) {
 		c = readchar();
 		if(c == '1') {
-			fb_enable_write(1);
+			fb_enable(1);
 			printf("Framebuffer is ON\n");
 		} else if(c == '0') {
-			fb_enable_write(0);
+			fb_enable(0);
 			printf("Framebuffer is OFF\n");
 		}
 	}
@@ -98,9 +99,10 @@ int main(void)
 	puts("Minimal video mixer software built "__DATE__" "__TIME__"\n");
 	
 	time_init();
+	fb_set_mode(FB_MODE_640_480);
 	dvisampler0_init_video();
 	dvisampler1_init_video();
-	fb_enable_write(1);
+	fb_enable(1);
 
 	while(1) {
 		dvisampler0_service();