Add source for compiling register write tests for firebeat.

source/register.s

@@ -0,0 +1,43 @@
+# Assembly code that is meant to be patched into memory location 0x8007ec5c of a BeatmaniaIII The Final executable
+# which converts the test screen DIPswitch code into a register write for experimenting with HW. Also, make sure to
+# patch location 0x80003b60 with the value 0x60 0x00 0x00 0x00 (NOP) to stop the WD thread from overwriting the
+# LEDs (this is a bug even in the test mode for a standard BMIII image, but we want to see what value we're writing
+# to the register).
+#
+# powerpc-linux-gnu-as -m403 -o register.o register.s
+# powerpc-linux-gnu-ld -e loc_register --oformat binary -o register.bin register.o
+# 
+# The resulting bin can be loaded into MAME like so, or patched onto a legit binary that was extracted using exe_utils:
+#
+# load hexify.bin,0x8007ec5c,0x4C
+
+    .section .text
+    .globl loc_register
+
+loc_register:
+    # Input location is R3, from previous code. 0x7D000500 is the register we are writing.
+    lis       %r12, 0x7D00
+    stb       %r3, 0x0500(%r12)
+
+    # Don't exit the loop, we will ignore the service/test prompt and spin forever.
+    li        %r3, 0x00000001
+
+loc_finished:   
+    # Done! We need nops to cover up original instructions, we need to
+    # cover 0x4C bytes.
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop