//==========================================================================
// This is the entrypoint from real-mode which functions exactly as it did
// before. Multiboot does its own runtime initialization, does some of its
// own things, and then calls common_boot.
void boot(int biosdev)
{
initialize_runtime();
// Enable A20 gate before accessing memory above 1Mb.
enableA20();
common_boot(biosdev);
}
// Starts off in the multiboot context 1 MB high but eventually gets into low memory
// and winds up with a bootdevice in eax which is all that boot() wants
// This lets the stack pointer remain very high.
// If we were to call boot directly from multiboot then the whole multiboot_info
// would be on the stack which would possibly be using way too much stack.
void multiboot_to_boot(int multiboot_magic, struct multiboot_info *mi_orig)
{
uint32_t bootdevice = hi_multiboot(multiboot_magic, mi_orig);
if(bootdevice != BAD_BOOT_DEVICE)
{
// boot only returns to do a chain load.
for(;;)
{ // NOTE: boot only uses the last byte (the drive number)
common_boot(bootdevice);
if(chainbootflag)
chainLoad();
else
waitThenReload();
}
}
// Avoid returning to high-memory address which isn't valid in the segment
// we are now in.
// Calling sleep() ensures the user ought to be able to use Ctrl+Alt+Del
// because the BIOS will have interrupts on.
for(;;)
sleep(10);
// NOTE: *IF* we needed to return we'd have to fix up our return address to
// be in low memory using the same trick as below.
// However, there doesn't seem to be any point in returning to assembly
// particularly when the remaining code merely halts the processor.
}