docs/DSP: Document behavior of LRS/SRS/SI with CR

1 files changed, 11 insertions, 7 deletions

diff --git a/docs/DSP/GameCube_DSP_Users_Manual/GameCube_DSP_Users_Manual.tex b/docs/DSP/GameCube_DSP_Users_Manual/GameCube_DSP_Users_Manual.tex
index 6980489b8c..615a834bc0 100644
--- a/docs/DSP/GameCube_DSP_Users_Manual/GameCube_DSP_Users_Manual.tex
+++ b/docs/DSP/GameCube_DSP_Users_Manual/GameCube_DSP_Users_Manual.tex
@@ -534,7 +534,7 @@ If the value is not zero, then the PC is modified by the value from call stack \
 
 \section{Config register}
 
-Its purpose is unknown at this time. It is written with \Value{0x00FF} and \Value{0x0004} values.
+Serves as a base offset for \Opcode{SRS} and \Opcode{LRS}.  Zelda uCode writes it with \Value{0x0004}, but otherwise it is usually \Value{0x00FF}.
 
 This is an 8-bit register.  Writes to the upper 8 bits are ignored and those bits always read back as 0.
 
@@ -2558,12 +2558,12 @@ A ``-'' indicates that the flag retains its previous value, a ``0'' indicates th
   \end{DSPOpcodeFormat}
 
   \begin{DSPOpcodeDescription}
-    \item Move value from data memory pointed by address \Address{M} (8-bit sign-extended) to register \Register{\$(0x18+D)}.
+    \item Move value from data memory pointed by address \Address{(\$cr << 8) | M} to register \Register{\$(0x18+D)}.
           Perform an additional operation depending on destination register.
   \end{DSPOpcodeDescription}
 
   \begin{DSPOpcodeOperation}
-    $(0x18+D) = MEM[M]
+    $(0x18+D) = MEM[($cr << 8) | M]
     $pc++
   \end{DSPOpcodeOperation}
 
@@ -3843,14 +3843,18 @@ A ``-'' indicates that the flag retains its previous value, a ``0'' indicates th
   \end{DSPOpcodeFormat}
 
   \begin{DSPOpcodeDescription}
-    \item Store 16-bit immediate value \Value{I} to a memory location pointed by address \Address{M} (\Address{M} is an 8-bit sign-extended value).
+    \item Store 16-bit immediate value \Value{I} to a memory location pointed by address \Address{0xFF00 | M}.
   \end{DSPOpcodeDescription}
 
   \begin{DSPOpcodeOperation}
-    MEM[M] = I
+    MEM[0xFF00 | M] = I
     $pc += 2
   \end{DSPOpcodeOperation}
 
+  \begin{DSPOpcodeNote}
+    \item Unlike \Opcode{LRS} and \Opcode{SRS}, \Opcode{SI} does not use \Register{\$cr} to decide the base address and instead always uses \Address{0xFF00}.
+  \end{DSPOpcodeNote}
+
   \DSPOpcodeFlagsUnchanged
 \end{DSPOpcode}
 
@@ -3979,12 +3983,12 @@ A ``-'' indicates that the flag retains its previous value, a ``0'' indicates th
   \end{DSPOpcodeFormat}
 
   \begin{DSPOpcodeDescription}
-    \item Store value from register \Register{\$(0x18+S)} to a memory pointed by address \Address{M} (8-bit sign-extended).
+    \item Store value from register \Register{\$(0x18+S)} to a memory pointed by address \Address{(\$cr << 8) | M}.
           Perform an additional operation depending on destination register.
   \end{DSPOpcodeDescription}
 
   \begin{DSPOpcodeOperation}
-    MEM[M] = $(0x18+S)
+    MEM[($cr << 8) | M] = $(0x18+S)
     $pc++
   \end{DSPOpcodeOperation}