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In the process I found a bug in the Mu compiler. Limitations of just asserting
the emitted code but not running it.
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It's bad enough that metadata comments are restricted to integer literals;
let's at least make them work on _all_ integer literals.
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Convert comments about magic constants into metadata.
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Metadata is always ignored. It's purely for documentation purposes. But
as long as Mu has no named constants it's starting to feel increasingly
essential.
I'm still not going to bother to add metadata to other parts of the language.
Let's see if we need them. Even though it's a little warty that the rules
vary throughout the stack:
- bare SubX: metadata everywhere
- SubX with syntax sugar: no metadata in calls or addressing-mode sigil-expressions
- Mu: metadata only for literal integers
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This was tedious for three reasons beyond the usual one of having to
track and update offsets several time while I debug:
- The Bochs troubles of the previous commit kept polluting my brain
even though they were irrelevant.
- I had to keep some changes locally to allow myself to use Bochs,
which polluted my working directory.
- I had to travel the long way to the realization that I'm not
actually initializing the stack anywhere. BIOS was starting my stack
off at 0x10000, which was promptly clobbered by my second read from
disk.
The good news: while I'm here I grow the interrupt descriptor table. So
I don't have to go through this exercise when I get back to supporting
the mouse.
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https://en.wikipedia.org/wiki/GNU_Unifont#The_.hex_font_format
http://unifoundry.com/unifont/index.html
Since GNU Unifont is covered under the GPL v2, so I believe is this repo.
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Bring baremetal variant up to date with recent changes.
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Switch survey_elf to the new approach.
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Go back to commit 7448.
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Snapshot: this approach of disambiguating /disp32 based on metadata doesn't
work. The `survey` phase runs after `pack`, which gets rid of most metadata.
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A new phase for baremetal compilations. Doesn't work yet, but it passes
all its tests, so we can add it to CI.
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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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