On Thu, Dec 20, 2007 at 01:31:06AM +0900, Kohsuke Ohtani wrote: > Hi Alex, > > >Has anyone booting prex with an image that's larger than 128kb? Any > >suggestions > >for what might be done? I'm considering trying to get grub or some other > >boot > >sector to load the image and see if that does anything.. > > I investigated this symptom today, and got the hang up reason. There are > two limitations about the size of boot image in the current Prex-i386 > version. > > 1) Boot Sector > A boot sector reads a file named "PREXOS" in the root directory. The > file image is copied to 0x40000 by using BIOS disk service. Since we can > use only conventional memory area with BIOS, the max file size is > limited to 384K (0xA0000 - 0x40000 = 0x60000) bytes. > > 2) Boot Loader > After reading image, the boot sector jumps to the entry point (at > 0x40000) of the boot loader. Then, the loader reads the raw file data > from memory and load the kernel/driver/task images into 0x10000. You can > find the second limitation here because the loader may overwrite itself > if the load image is too large. In this case, the total image size is > limited to 192K (0x40000 - 0x10000 = 0x30000) bytes. > > I'll apply the following fixes in the next Prex release. > > - Change the boot loader to move its code and whole file image to > 0x100000. So, we can use the address from 0x10000 to 0xA0000. > (Image max: 192K -> 576K bytes) > > - Change the boot sector to copy the file into 0x30000. > (File max: 384K -> 448K bytes) > Cool! I figured it was something related to image size, I'm happy I was right about that. Would it be possible to get a patch for these changes?
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