| Commit message (Collapse) | Author | Age | Files | Lines |
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We need a few pages of data for the keyboard mappings.
If I moved them to some later address I'd be able to keep the nice round
starting address unchanged. But that seems like a superficial aesthetic
concern. There's really no value in having an array of hex bytes represented
in SubX rather than just raw hex. And it's better to colocate data near
the handler code which uses it (and which runs instructions SubX doesn't
support).
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This currently works on Qemu, but not on Bochs. I'm now trying to make
sense of https://wiki.osdev.org/Bochs_VBE_Extensions#Using_a_linear_frame_buffer_.28LFB.29
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0xa0000 only contains a single bank's worth of memory-mapped video RAM.
The LFB is supposed to have everything.
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This works, but colors are unexpected. 0xff isn't white. Lots of colors
are black. Perhaps I need to initialize a palette.
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Design choice: all programs will use a graphics mode (1280x1024) with 256
colors. That should be fairly widely available. (It turns out text modes
larger than 80x25 are not widely available even among modern emulators.
Mu will need fonts sooner rather than later.)
Mu will never try to be smart and do things like autodetect your hardware.
We _will_ help you modify Mu for your hardware.
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Turns out the default 8MB stack is quite enough for the programs I'm
currently running.
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Some manual tweaks to boot.hex.html
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https://stackoverflow.com/questions/37618111/keyboard-irq-within-an-x86-kernel
is right, no need to mess with the status port at the start.
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I think https://stackoverflow.com/questions/37618111/keyboard-irq-within-an-x86-kernel
has more insight to provide. Among other things the comment about grub
may answer the distinction between entry 0x21 and entry 9.
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Snapshot. Keyboard interrupt being triggered.
This was hard to debug until https://stackoverflow.com/questions/37618111/keyboard-irq-within-an-x86-kernel
reminded me that I'd forgotten to enable IRQ1 on port 0x21.
For a while I was confused by never hitting a breakpoint at the start of
the keyboard handler. Then I found https://sourceforge.net/p/bochs/discussion/39592/thread/5e397455
and started skipping one instruction in my breakpoint.
I still don't understand the discrepancy between some people installing
the handler at entry 9, and others installing at entry 0x21 = 33.
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Turns out we just need a null handler at offset 8 rather than offset 9.
If the keyboard handler is indeed at offset 9 as
https://alex.dzyoba.com/blog/os-interrupts says (I don't understand
why), then the clock handler's at offset 8, which makes sense.
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Looks like the reset loops stop if we create null handlers for the first
10 indexes in the IDT.
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Ok, we're back at the reset loop. Let's keep going; maybe having a decent
keyboard handler will fix it.
The bug I fixed here was caused by misunderstanding what m16&32 mean in
the Intel manual. It's still a regular regmem operand that uses all of
the ModR/M byte (which can be interpreted in 16-bit mode, adding to the
complication). It's just constrained to not allow direct addressing (mod 00).
I needed to better internalize the format of the instruction set references
at the start of Volume 2, Chapter 3.
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I'm now back at the state of commit 7382 (including 7376). The existing
print to screen surprisingly seems to work without reset-looping, but when
I step through I notice that the lidt isn't doing what I expect.
Desired: at address 0x7cce, the processor executes:
0f 01 1e 00 7f # lidt ds:*idt_descriptor
Observed: at address 0x7cce, the processor executes:
0f 01 1e # lidt ds:*esi
As a result the next instruction is:
00 7f fb
So the `fb` isn't interpreted to enable interrupts. So the problem of commit
7376 is latent.
Past this point the instruction stream is lined up again, and everything
occurs as it should. Purely by chance.
I fully expect all hell to break loose again, like it did in commit 7376,
once I debug the lidt encoding. There's still something I don't understand
about enabling interrupts. Perhaps I need to fill in more entries in the
table.
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Redo commit 7381. There was a bug.
Current state: commit 7381 excluding 7376.
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Commit 7380 excluding 7376.
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Commit 7379 excluding 7376.
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Currently at commit 7378 (reset the A20 address line) except without 7376
(enabling interrupts).
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Currently at commit 7377 except without 7376 (enabling interrupts). Works
as advertised.
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Turns out I've been "testing" with a stale file since commit 7373. We need
to go over everything since then.
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Turns out we only had access to 50% of RAM so far. Closing my nose and
moving right along..
Though this _does_ give me practice interacting with ports. That'll be
handy for the keyboard.
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Ooh, look at that, the device number comes conveniently initialized in
the right register. No need to hardcode it.
https://wiki.osdev.org/MBR_(x86)
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A little more robustness after reading https://stackoverflow.com/questions/43786251/int-13h-42h-doesnt-load-anything-in-bochs/43787939#43787939
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apps/boot.hex doesn't need much by way of syntax highlighting. Have it
work even for people who haven't installed subx.vim
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