Heavy RAM usage causes glitches on video output

The display subsystem(vpss) is a real time master trying to access the DDR. While another master(in your case the ARM, since memset is also causing it), is also trying to access it. Ideally the real-time master should have higher priority, and should not lead to any glitches. But since you are using only one bank of DDR memory this cannot be ruled out.

Trying to balance loads by using the other DDR banks may help.

Thanks for the fast response :-)

I tried to set highest priority to the display process (-20) och lowest to the test process (the process that performs memset()) using nice and renice, but the problem persists. I agree, the problem seems to be priority related. There is only one bank on the board, so we can not load balance using another bank.

Is i possible to give the VPSS higher priority than the ARM?

/Emil

IF the reason for the glitch is like I stated earlier, giving higher priority to display process using nice will not help. The HDVPSS is a hardware, and hence will not be influenced by any software process priortiy. There are some memory interfaces inside the device that will determine which hardware will have priority to the DDR. Since I am not an expert on this particular device I cannot help you with these settings.

What is the operation that you are doing using the ARM. Which is the memory area that you are trying to access. If you are trying to access the display buffers, then these are usually not data-cached on ARM and hence will lead to heavy DDR load. The same kind of accesses on a cached buffer(got using malloc) will lead to much better DDR accesses.

What is the size of your framebuffer(display resolution) ?

These are the stats we get from the application which sets up the DVO as a framebuffer.

Resolution = 480x800
Virtual Resolution = 480x800
bites per pixel = 24
vinfo.red.length= 8, vinfo.green.length= 8, vinfo.blue.length= 8
vinfo.transp.length = 0
vinfo.transp.offset = 0
vinfo.red.length = 8
vinfo.red.offset = 16
vinfo.green.length = 8
vinfo.green.offset = 8
vinfo.blue.length = 8
vinfo.blue.offset = 0
Line length = 1440
Physical Address = 88dd2000
Buffer Length = 16777216
Resolution = 480x800
bites per pixel = 24

And the frame buffer is set up using the following code:

        file_fb1 = open(device_name/*"/dev/fb0"*/, O_RDWR);
        if (file_fb1 == -1) {
                pabort( "failed to open display device\n");
        }
        printf("%s temporary opened\n", device_name);
        usleep(10000);
        
        printf("Configuring linux for the display DVO2 (Physical port VOUT0)\n");
        // Turn off display and graphics
        fp = fopen("/sys/devices/platform/vpss/graphics1/enabled", "w");
        fprintf(fp, "0\n");
        fclose(fp);
        usleep(10000);
        printf("Turn off display and graphics\n");
        fp = fopen("/sys/devices/platform/vpss/display1/enabled", "w");
        fprintf(fp, "0\n");
        fclose(fp);
        usleep(10000);
        
        // Configure the framebuffer1
        printf("Configure the framebuffer1\n");
        fp = fopen("/sys/class/graphics/fb1/bits_per_pixel", "w");
        fprintf(fp, "24\n");
        fclose(fp);
        fp = fopen("/sys/class/graphics/fb1/virtual_size", "w");
        fprintf(fp, "480,800\n");
        fclose(fp);
        usleep(10000);
        
        // Configure the display1 according to our display
        printf("Configure the display1 according to our display\n");
        fp = fopen("/sys/devices/platform/vpss/display1/clksrc", "w");
        fprintf(fp, "dclk\n");
        fclose(fp);
        
        fp = fopen("/sys/devices/platform/vpss/display1/mode", "w");
        fprintf(fp, "mobill\n");
        fclose(fp);
        
        fp = fopen("/sys/devices/platform/vpss/display1/output", "w");
        fprintf(fp, "triplediscrete,rgb888,0/0/1/1\n");
        fclose(fp);
        
        usleep(1000000);
        
        // Configure the graphics1 to be connected to display1 (DVO2 -> VOUT0 port). You must configure the display1 first for this to
        
        // Turn on display. Has to be done before /sys/devices/platform/vpss/graphics1/nodes can be changed
        printf("Turn on display. \n");
        fp = fopen("/sys/devices/platform/vpss/display1/enabled", "w");
        fprintf(fp, "1\n");
        fclose(fp);
        usleep(10000);
        
        // Connect the fb1/graphics1 with display1
        fp = fopen("/sys/devices/platform/vpss/graphics1/nodes", "w");
        fprintf(fp, "1:dvo2\n");
        fclose(fp);
        usleep(10000);

        // Turn on graphics
        fp = fopen("/sys/devices/platform/vpss/graphics1/enabled", "w");
        fprintf(fp, "1\n");
        fclose(fp);
        usleep(10000);

        close(file_fb1);