diff --git a/src/xenia/cpu/ppc/testing/README.md b/src/xenia/cpu/ppc/testing/README.md
index e35adf40c..7bb2f52e2 100644
--- a/src/xenia/cpu/ppc/testing/README.md
+++ b/src/xenia/cpu/ppc/testing/README.md
@@ -5,25 +5,29 @@ runner.
 
 Each test is structured as a source `[name].s` PPC assembly file and the
 generated outputs. The outputs are made using the custom build of binutils
-setup when `xenia-build setup` is called and are checked in to make it easier
+setup when `xenia-build gentests` is called and are checked in to make it easier
 to run the tests on Windows.
 
 Tests are run using the `xenia-test` app or via `xenia-build test`.
 
 ## Execution
 
-The test binary is placed into memory at `0x82010000` and all other memory is
-zeroed.
+**On Xenia**: The test binary is placed into memory at `0x82010000` and all other
+memory is zeroed.
 
 All registers are reset to zero. In order to provide useful inputs tests can
-specify `# REGISTER_IN` values.
+specify `#_ REGISTER_IN` values.
 
-The code is jumped into at the starting address and executed until the last
-instruction in the input file is reached.
+The code is jumped into at the starting address and executed until a `blr`
+instruction is encountered.
 
-After all instructions complete any `# REGISTER_OUT` values are checked and if
+After all instructions complete any `#_ REGISTER_OUT` values are checked and if
 they do not match the test is failed.
 
+## Registers
+
+All registers **except lr, r1, and r13** are available for usage by tests.
+
 ## Annotations
 
 Annotations can appear at any line in a file. If a number is required it can
@@ -32,21 +36,21 @@ be in either hex or decimal form, or IEEE if floating-point.
 ### REGISTER_IN
 
 ```
-# REGISTER_IN [register name] [register value]
+#_ REGISTER_IN [register name] [register value]
 ```
 
 Sets the value of a register prior to executing the instructions.
 
 Examples:
 ```
-# REGISTER_IN r4 0x1234
-# REGISTER_IN r4 5678
+#_ REGISTER_IN r4 0x1234
+#_ REGISTER_IN r4 5678
 ```
 
 ### REGISTER_OUT
 
 ```
-# REGISTER_OUT [register name] [register value]
+#_ REGISTER_OUT [register name] [register value]
 ```
 
 Defines the expected register value when the instructions have executed.
@@ -55,7 +59,7 @@ the value given here the test will fail.
 
 Examples:
 ```
-# REGISTER_OUT r3 123
+#_ REGISTER_OUT r3 123
 ```
 
 TODO: memory setup/assertions
diff --git a/src/xenia/cpu/ppc/testing/instr_vpkd3d128.s b/src/xenia/cpu/ppc/testing/instr_vpkd3d128.s
index c366b3ab2..7156dc4a7 100644
--- a/src/xenia/cpu/ppc/testing/instr_vpkd3d128.s
+++ b/src/xenia/cpu/ppc/testing/instr_vpkd3d128.s
@@ -4,7 +4,7 @@
 #   1 = PACK_TYPE_SHORT_2
 #   2 = PACK_TYPE_2_10_10_10
 #   3 = PACK_TYPE_FLOAT16_2
-#   4 = ?
+#   4 = PACK_TYPE_SHORT_4
 #   5 = PACK_TYPE_FLOAT16_4
 # mask:
 #   must not be zero