Didj and Explorer: boot pixel format

Tutorial to help the user set a framebuffer pixel format that will display the boot logo correctly.

The excellent work by nirvous has given us a frame buffer driver, this is a work in progress, it currently has some hard-coded settings to make it work primarily with the gpsp gba emulator, so things like the linux boot logo don't show up in the correct colours (my tux in 565 mode has a bit of a tint, and the background for the layer is red).

Prerequisites Working toolchain Explorer kernel Sources with lf1000fb drivers already patched in correctly set environment variables lf1000 frame buffer drivers from nirvous github gpsp sources from nirvous github (optional)

The reason for the boot logo being skewed is the default pixel format and some other non default settings, the available pixel formats are:

RGB565-8bit (not sure what this mode is exactly) RGB565-16bit (Default) RGB888-24bit (this and 32bit are pretty much used universally for images like jpg,bmp,png etc.) ABGR888-32bit (like BGR888 24bit but with a transparency byte?)

These are currently dealt with in a switch case in lf1000fb.c in the function set_mode:

static void set_mode(struct lf1000fb_info *fbi)

with a test to see what bits_per_pixel is set to, bits_per_pixel is hardcoded to take BITSPP which is derived from BYTESPP*8 elsewhere in the code.

The important parts here are the offset, length and the pix_fmt variables. There is a list of the possible pix_fmt values in lf1000fb.h, I have commented the ones we use above, you can also see where BYTESPP and how BITSPP are set:

/* Formats: * 	RGB565		= 0x4432, // 16 bits per pixel mode 2 BYTESPP BGR565		= 0xC432, XRGB1555	= 0x4342, XBGR1555	= 0xC342, XRGB4444	= 0x4211, XBGR4444	= 0xC211, XRGB8332	= 0x4120, XBGR8332	= 0xC120, ARGB1555	= 0x3342, ABGR1555	= 0xB342, ARGB4444	= 0x2211, ABGR4444	= 0xA211, ARGB8332	= 0x1120, ABGR8332	= 0x9120, RGB888	= 0x4653, // 24 bits per pixel mode 3 BYTESPP BGR888	= 0xC653, XRGB8888	= 0x4653, XBGR8888	= 0xC653, ARGB8888	= 0x0653, ABGR8888	= 0x8653, // 32 bits per pixel mode 4 BYTESPP PTRGB565	= 0x443A //  8 bits per pixel mode 1 BYTESPP * */
 * 1) define BYTESPP				2
 * 1) define BITSPP				BYTESPP*8
 * 2) define VISUALTYPE			FB_VISUAL_TRUECOLOR //FB_VISUAL_PSEUDOCOLOR, FB_VISUAL_TRUECOLOR

We now know what modes we are using, changing the default mode should be easy, change BYTESPP to be an integer between 1 and 4, as I'm using SDL and I want to display some png and bmp images I tested with 3.

Oh Dear, one Tux with blue feet and a blue background, testing my app and the colours in my image are well off :/ what's going wrong? Look at the code for BYTESPP = 3, 24bit:

fbi->fb.var.red.offset     = 0;//0 for bgr. 16 for rgb fbi->fb.var.red.length     = 8; fbi->fb.var.green.offset   = 8; fbi->fb.var.green.length   = 8; fbi->fb.var.blue.offset    = 16;//16 for bgr. 0 for rgb fbi->fb.var.blue.length    = 8; fbi->fb.var.transp.offset  = 0; fbi->fb.var.transp.length  = 0; fbi->pix_fmt               = 0x4653;

Its been nicely commented so we can easily see what is happening, it looks like the pix_fmt is correctly set for RGB888, the BYTESPP are set correctly, so from the comments its definitely the offsets, swap them back so they are RGB

fbi->fb.var.red.offset     = 16;//0 for bgr. 16 for rgb ...            fbi->fb.var.blue.offset     = 0;//16 for bgr. 0 for rgb Time to recompile your kernel, Success, tux displays correctly, getting a blue background this time around, testing the SDL app and I get my image displayed in glorious technicolour. Great, what about other apps?

I'm also testing with gpsp, in 565 mode, gpsp works fine, with or without the fb driver. In 24bit or 32bit mode using the fb driver gpsp is displayed wrong, so it appears that gpsp isn't setting the mode settings correctly when its using the framebuffer driver. What do we do about it?

We know that gpsp will display correctly if it's using the lf1000 mlc/dpc drivers, so lets take a look in the /lf1000 folder at lf1000.c from the gpsp sources, the video init functions are what we need to look at:

static void fb_video_init {  struct fb_fix_screeninfo fbfix; int i, ret; fbdev = open("/dev/fb0", O_RDWR); if (fbdev < 0) { perror("can't open fbdev"); printf("attempting mlc\n"); //nirvous - added support for MLC driver fbdev = open("/dev/layer0", O_RDWR); if (fbdev < 0) { perror("can't open mlc"); exit(1); } 	fb_paddr[0] = ioctl(fbdev, MLC_IOCQADDRESS, 0); if (ret == -1) { 		perror("ioctl(fbdev) failed"); exit(1); } //capture original mlc settings, then change to RGB565 original_mlcformat = ioctl(fbdev, MLC_IOCQFORMAT, 0); original_mlchstride = ioctl(fbdev, MLC_IOCQHSTRIDE, 0); original_mlcvstride = ioctl(fbdev, MLC_IOCQVSTRIDE, 0); ioctl(fbdev, MLC_IOCTFORMAT, 0x4432); ioctl(fbdev, MLC_IOCTHSTRIDE, 2); ioctl(fbdev, MLC_IOCTVSTRIDE, 320*2); ioctl(fbdev, MLC_IOCTDIRTY, 0); printf("mlc framebuffer: @ %08lx\n", fb_paddr[0]); }  else { 	 ret = ioctl(fbdev, FBIOGET_FSCREENINFO, &fbfix); if (ret == -1) { 		perror("ioctl(fbdev) failed"); exit(1); } 	 printf("framebuffer: \"%s\" @ %08lx\n", fbfix.id, fbfix.smem_start); fb_paddr[0] = fbfix.smem_start; }

The basic breakdown of the code is: try to open the framebuffer /dev/fb0 if we fail, try the mlc driver if we get mlc success then store the original format settings and set 565 mode for gpsp if we succeeded in opening the framebuffer device we just assume we're in the right mode....

That last bit is the issue, we never set the mode if we use the framebuffer driver.

Simple to rectify in this instance, copy the mlc code for handling the mode and format settings, the else should now look like this: else { 	 ret = ioctl(fbdev, FBIOGET_FSCREENINFO, &fbfix); if (ret == -1) { 		perror("ioctl(fbdev) failed"); exit(1); } // copied and pasted by reggie //capture original mlc settings, then change to RGB565 ioctl(fbdev, MLC_IOCTENABLE, 1); // added by reggie original_mlcformat = ioctl(fbdev, MLC_IOCQFORMAT, 0); original_mlchstride = ioctl(fbdev, MLC_IOCQHSTRIDE, 0); original_mlcvstride = ioctl(fbdev, MLC_IOCQVSTRIDE, 0); ioctl(fbdev, MLC_IOCTFORMAT, 0x4432); ioctl(fbdev, MLC_IOCTHSTRIDE, 2); ioctl(fbdev, MLC_IOCTVSTRIDE, 320*2); ioctl(fbdev, MLC_IOCTDIRTY, 0); printf("framebuffer: \"%s\" @ %08lx\n", fbfix.id, fbfix.smem_start); fb_paddr[0] = fbfix.smem_start; }

Testing it now shows that gpsp will work with 24 and 32bit modes, we get the added bonus that we've cleaned up another little gpsp quirk, quitting the app. no longer stops other apps and gpsp from displaying an image, before this (at least for me) gpsp would load fine the first time, then anything else I loaded after that wouldn't display anything on screen.

I've added the MLC_IOCTENABLE control to the routine as well, this is used because we are going to disable the layer on exit, this will tidy up the screen when gpsp has finished but obviously breaks other apps that don't enable the layer when they open the framebuffer, we should really be doing this in the framebuffer driver I think.

static void fb_video_exit {  int ret; /* switch to default fb mem, turn portrait off */ //nirvous comments out support for layer1 //gpsp_gp2x_memregl[0x406C>>2] = fb_paddr[0]; //gpsp_gp2x_memregl[0x4058>>2] |= 0x10; //nirvous adds support for layer0 gpsp_gp2x_memregl[0x4038>>2] = fb_paddr[0]; gpsp_gp2x_memregl[0x4024>>2] |= 0x10; wiz_lcd_set_portrait(0); ret = ioctl(fbdev, MLC_IOCQADDRESS, 0); if (ret == -1) { 	//nirvous - restore original mlc settings ioctl(fbdev, MLC_IOCTFORMAT, original_mlcformat); ioctl(fbdev, MLC_IOCTHSTRIDE, original_mlchstride); ioctl(fbdev, MLC_IOCTVSTRIDE, original_mlcvstride); ioctl(fbdev, MLC_IOCTENABLE, 0); // added by reggie ioctl(fbdev, MLC_IOCTDIRTY, 0); close(fbdev); }  else { 	//nirvous - restore original mlc settings ioctl(fbdev, MLC_IOCTFORMAT, original_mlcformat); ioctl(fbdev, MLC_IOCTHSTRIDE, original_mlchstride); ioctl(fbdev, MLC_IOCTVSTRIDE, original_mlcvstride); ioctl(fbdev, MLC_IOCTENABLE, 0); // added by reggie ioctl(fbdev, MLC_IOCTDIRTY, 0); close(fbdev); }	 }

Notes

I think we need a better method for doing things, changing the background colour via ioctl doesn't seem to do much, even though the background register displays the change when queried, it might be more useful if we use layer0 as a seperate background layer, and work with either layer 1 or layer 2 as our main layer, I wonder if it's possible to allow us to pass fb1 and fb2 to the driver and have it react accordingly? Or pass the driver an 'active layer' flag?