The implementation of the A20 wraparound check was off in some way,
which is why the new implementation was copied from osdev.org, just
using minor modifications to the label naming.
The value of the GDTR register was set to be 8 bytes too small, with
the effect that an accurate emulation software would error out because
of trying to read over the buffer size, as was noticed when using KVM.
This was due to the perception that the 0th index wouldn't be taken
into account; for that reason, the length of the GDTR was one index
short of what it should've been.
With this change, the driver's setup function only has to be added
to the 'driver_init_functions'-array and it will be called once
'setup_drivers' is called.
The driver setup, which in turn calls all the drivers' setup functions
wasn't being called until now. Now, it is included and being called.
The test text which was used to test some display functions in older
revisions is also gone now.
The setup_drivers routine existed locally for some time now, so now
it also exists in the repository. It has gone through two iterations:
1. The drivers are all listed in a null-terminated array of function
pointers to initialization functions (this didn't work and the time
for debugging just wasn't there).
2. All drivers (currently, only the PCI driver, because that's the
only one that exists) are initialized after each other; their
initialization functions are called manually.
It might be possible that the bug from the first iteration was due to
the memory space being offset by 128 or 256 bytes; it might be useful
to use that concept again because then, it will be easier to add new
drivers. That's not of high importance now, though.
The newly added utility routine reads the content of a known PCI
device's register given the index assigned to the device during
enumeration and the index of the register (and the PCI driver area,
but that is implied).
Because the calculation of the byte offset within the framebuffer was
wrong, the framebuffer could only be written to on the first line.
That is now fixed.
The function which is added with this commit writes a caller-supplied
hexadecimal string of a caller-supplied length to the display, nibble
by nibble, leaving the background black and making the text white.
The error in the GDT caused the whole memory space to be offset by
128B or 256B (It's not entirely sure which one of those). This was
only made visible by later changes, but now it's fixed.
This commit changes the final jump from the bootsector to the second
stage (the partition which gets loaded completely) to be a near jump.
That's important to keep consistency with protected mode.
This commit deletes the gdt.asm for the i386 architecture as it was
quite buggy in that state. In a short while, the real GDT code which
works is going to be committed.
This commit adds a README.md file for the loader partition in the i386
architecture version. The README contains basic information about what
the loader partition has to do and to some degree on how it should be
accomplishing those tasks.
It is just general information which can be useful to have for looking
information up after some time.
This commit adds a build script for the loader partition. Currently,
it is very simplistic, but it works for assembling the entry.asm,
which in turn includes all other files.
This commit adds the entry point for the second stage of the loader.
It currently doesn't contain a lot of code, but it will have to expand
in the next bit of time.
This commit adds the well known primitive memory functions:
- Copy Memory
- Compare Memory for being equal
- Set Memory to a value
It also adds a math utility file at the according location.
This commit adds a check for whether the A20 line is usable; checking
whether more than one megabyte of RAM can be used. If it isn't usable,
it currently isn't activated, but rather, the boot process is stopped.
This commit adds a basic .gitignore which only contains machine code
file endings; files which shouldn't be committed as they're better to
be distributed in other ways.
Eric-Paul Ickhorn