7437 - baremetal: draw pixel on keyboard event

It's now clear that our keyboard handler doesn't trigger after the first
event.

2 files changed, 68 insertions, 7 deletions

diff --git a/baremetal/boot.hex b/baremetal/boot.hex
index 6090eef3..cae8b456 100644
--- a/baremetal/boot.hex
+++ b/baremetal/boot.hex
@@ -240,7 +240,7 @@ e9 fb ff  # loop forever
   # . var index/ecx: byte
   8a  # copy m8 at r32 to r8
     0d  # 00/mod/indirect 001/r8/cl 101/rm32/use-disp32
-    cf 7d 00 00  # disp32 [label]
+    ce 7d 00 00  # disp32 [label]
   # . al = *(keyboard buffer + index)
   8a  # copy m8 at r32 to r8
     81  # 10/mod/*+disp32 000/r8/al 001/rm32/ecx
@@ -263,12 +263,12 @@ e9 fb ff  # loop forever
   # increment index
   fe  # increment byte
     05  # 00/mod/indirect 000/subop/increment 101/rm32/use-disp32
-    cf 7d 00 00  # disp32 [label]
+    ce 7d 00 00  # disp32 [label]
   # clear top nibble of index (keyboard buffer is circular)
   80  # and byte
     25  # 00/mod/indirect 100/subop/and 101/rm32/use-disp32
-    cf 7d 00 00  # disp32 [label]
-    f0  # imm8
+    ce 7d 00 00  # disp32 [label]
+    0f  # imm8
 # 14d:
   # epilogue
   61  # pop all registers
@@ -284,12 +284,16 @@ e9 fb ff  # loop forever
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
-00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+00 00 00 00 00 00 00 00 00 00 00 00 00 00
 
+# 1ce:
+# var keyboard circular buffer
+# write index: nibble
+00
 # 1cf:
-# var keyboard circular buffer index: nibble
+# read index: nibble
 00
-# var keyboard circular buffer: byte[16]
+# circular buffer: byte[16]
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 
 # padding
diff --git a/baremetal/ex3.hex b/baremetal/ex3.hex
new file mode 100644
index 00000000..79fe8cf8
--- /dev/null
+++ b/baremetal/ex3.hex
@@ -0,0 +1,57 @@
+# Draw pixels in response to keyboard events.
+#
+# To run, first prepare a realistically sized disk image:
+#   dd if=/dev/zero of=disk.img count=20160  # 512-byte sectors, so 10MB
+# Load the program on the disk image:
+#   cat baremetal/boot.hex baremetal/ex3.hex  |./bootstrap run apps/hex  > a.bin
+#   dd if=a.bin of=disk.img conv=notrunc
+# To run:
+#   qemu-system-i386 disk.img
+# Or:
+#   bochs -f apps/boot.bochsrc  # boot.bochsrc loads disk.img
+
+# main:  (address 0x8800)
+
+# eax <- LFB
+8b  # copy *rm32 to r32
+  05  # 00/mod/indirect 000/r32/eax 101/rm32/use-disp32
+  28 7f 00 00 # disp32 [label]
+
+# var read index/ecx: byte = 0
+31 c9  # ecx <- xor ecx;  11/direct 001/r32/ecx 001/rm32/ecx
+
+# $loop:
+  # CL = *read index
+  8a  # copy m8 at r32 to r8
+    0d  # 00/mod/indirect 001/r8/cl 101/rm32/use-disp32
+    cf 7d 00 00  # disp32 [label]
+  # CL = *(keyboard buffer + ecx)
+  8a  # copy m8 at r32 to r8
+    89  # 10/mod/*+disp32 001/r8/cl 001/rm32/ecx
+    d0 7d 00 00  # disp32 [label]
+  # if (CL == 0) loop (spin loop)
+  80
+    f9  # 11/mod/direct 111/subop/compare 001/rm8/CL
+    00  # imm8
+  74 ef  # loop -17 [label]
+# offset 0x19:
+  # otherwise increment read index
+  fe  # increment byte
+    05  # 00/mod/indirect 000/subop/increment 101/rm32/use-disp32
+    cf 7d 00 00  # disp32 [label]
+  # clear top nibble of index (keyboard buffer is circular)
+  80  # and byte
+    25  # 00/mod/indirect 100/subop/and 101/rm32/use-disp32
+    cf 7d 00 00  # disp32 [label]
+    0f  # imm8
+  # print a pixel in fluorescent green
+  c6  # copy imm8 to m8 at rm32
+    00  # 00/mod/indirect 000/subop 000/rm32/eax
+    31  # imm32
+  40  # increment eax
+  eb dc # loop -36 [label]
+
+# $break:
+e9 fb ff ff ff  # hang indefinitely
+
+# vim:ft=subx