7842 - new directory organization

Baremetal is now the default build target and therefore has its sources
at the top-level. Baremetal programs build using the phase-2 Mu toolchain
that requires a Linux kernel. This phase-2 codebase which used to be at
the top-level is now under the linux/ directory. Finally, the phase-2 toolchain,
while self-hosting, has a way to bootstrap from a C implementation, which
is now stored in linux/bootstrap. The bootstrap C implementation uses some
literate programming tools that are now in linux/bootstrap/tools.

So the whole thing has gotten inverted. Each directory should build one
artifact and include the main sources (along with standard library). Tools
used for building it are relegated to sub-directories, even though those
tools are often useful in their own right, and have had lots of interesting
programs written using them.

A couple of things have gotten dropped in this process:
  - I had old ways to run on just a Linux kernel, or with a Soso kernel.
    No more.
  - I had some old tooling for running a single test at the cursor. I haven't
    used that lately. Maybe I'll bring it back one day.

The reorg isn't done yet. Still to do:
  - redo documentation everywhere. All the README files, all other markdown,
    particularly vocabulary.md.
  - clean up how-to-run comments at the start of programs everywhere
  - rethink what to do with the html/ directory. Do we even want to keep
    supporting it?

In spite of these shortcomings, all the scripts at the top-level, linux/
and linux/bootstrap are working. The names of the scripts also feel reasonable.
This is a good milestone to take stock at.

1 files changed, 48 insertions, 0 deletions

diff --git a/102keyboard.subx b/102keyboard.subx
new file mode 100644
index 00000000..df74c8e7
--- /dev/null
+++ b/102keyboard.subx
@@ -0,0 +1,48 @@
+# check keyboard for a key
+# return 0 on no keypress or unrecognized key
+#
+# We need to do this in machine code because Mu doesn't have global variables
+# yet (for the keyboard buffer).
+
+== code
+
+read-key:  # kbd: (addr keyboard) -> result/eax: byte
+    # . prologue
+    55/push-ebp
+    89/<- %ebp 4/r32/esp
+    # . save registers
+    51/push-ecx
+    # result = 0
+    b8/copy-to-eax 0/imm32
+    # ecx = keyboard
+    8b/-> *(ebp+8) 1/r32/ecx
+    81 7/subop/compare %ecx 0/imm32
+    {
+      75/jump-if-!= break/disp8
+      # var read/ecx: byte = keyboard buffer's read index
+      8b/-> *0x802c 1/r32/CL  # keyboard-buffer-read
+      # var next-key/eax: byte = *(keyboard buffer + ecx)
+      8a/byte-> *(ecx+0x8030) 0/r32/AL  # keyboard-buffer-data
+      # if (next-key != 0) lock and remove from keyboard buffer
+      81 7/subop/compare %eax 0/imm32
+      {
+        74/jump-if-= break/disp8
+        # TODO: add some instructions in this block to SubX if we ever want to
+        # use bootstrap on baremetal programs
+        fa/disable-interrupts
+        c6 0/subop/copy-byte *(ecx+0x8030) 0/imm8  # keyboard-buffer-data
+        ff 0/subop/increment *0x802c  # keyboard-buffer-read
+        81 4/subop/and *0x802c 0xf/imm32  # keyboard-buffer-read
+        fb/enable-interrupts
+      }
+      # return
+      eb $read-key:end/disp8
+    }
+    # TODO: fake keyboard
+$read-key:end:
+    # . restore registers
+    59/pop-to-ecx
+    # . epilogue
+    89/<- %esp 5/r32/ebp
+    5d/pop-to-ebp
+    c3/return