7462 - SubX version of baremetal/ex2.subx

apps/survey_baremetal.subx

@@ -1143,7 +1143,7 @@ $emit-output:emit-disp8:
     # emit-hex(out, *address - address-of-next-instruction, 1)
     # . . push args
     68/push  1/imm32
-    8b/copy                         1/mod/*+disp8   6/rm32/esi    .           .             .           0/r32/eax   8/disp8         .                 # copy *(esi+8) to eax
+    8b/copy                         0/mod/indirect  6/rm32/esi    .           .             .           0/r32/eax   .               .                 # copy *esi to eax
     29/subtract                     3/mod/direct    0/rm32/eax    .           .             .           3/r32/ebx   .               .                 # subtract ebx from eax
     50/push-eax
     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)

baremetal/ex2.subx

@@ -0,0 +1,35 @@
+# Test out the video mode by filling in the screen with pixels.
+#
+# To build a disk image:
+#   ./translate_subx_baremetal baremetal/ex2.subx    # emits disk.img
+# To run:
+#   qemu-system-i386 disk.img
+# Or:
+#   bochs -f baremetal/boot.bochsrc  # boot.bochsrc loads disk.img
+
+# main:  (address 0x8800)
+
+== code
+
+# ecx <- start of video memory
+8b/-> 0/mod/indirect 5/rm32/use-disp32 0x7f28/disp32/video-memory  1/r32/ecx
+
+# eax <- final pixel of video memory
+8d/copy-address *(ecx + 0x0bffff) 0/r32/eax  # 0xbffff = 1024*768 - 1
+
+# for each pixel in video memory
+{
+  39/compare %eax 1/r32/ecx
+  7c/jump-if-< break/disp8
+  # write its column number to it
+  88/byte<- *eax 0/r32/AL
+  48/decrement-eax
+  eb/jump loop/disp8
+}
+
+# hang indefinitely
+{
+  eb/jump loop/disp8
+}
+
+# vim:ft=subx