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

Source/DSPSpy/tests/cr_test.ds

@@ -0,0 +1,81 @@
+incdir "tests"
+include "dsp_base.inc"
+
+; Tests the behavior of SI, SRS, and LRS when CR is changed
+
+; Register that is writable but with contents that doesn't matter (COEF_A1_0)
+TEST_REG: equ 0xFFA0 ; 0xFF00 (not writable)
+; This is separate because SRS and SI currently require value 0..7f or ff80..ffff,
+; though the actual behavior doesn't match that
+TEST_ADDR: equ 0xFFA0 ; 0x0000
+; Memory addresses
+TEST_MEM: equ 0x00A0 ; 0x0000
+TEST_MEM_2: equ 0x01A0 ; 0x0100
+
+	LRI $AC0.L, #0xf00f
+	SR @TEST_REG, $AC0.L
+	SR @TEST_MEM, $AC0.L
+	SR @TEST_MEM_2, $AC0.L
+	CALL send_regs
+
+	; Observed: writes to TEST_REG
+	SI @TEST_ADDR, #0xf11f
+	CALL send_regs
+
+	LRI $AC0.L, #0xf22f
+	; Observed: writes to TEST_REG
+	SRS @TEST_ADDR, $AC0.L
+	CALL send_regs
+
+	LRI $CR, #0x0000
+	; Observed: still writes to TEST_REG
+	SI @TEST_ADDR, #0xf33f
+	CALL send_regs
+
+	LRI $AC0.L, #0xf44f
+	; Observed: writes to TEST_MEM
+	SRS @TEST_ADDR, $AC0.L
+	CALL send_regs
+
+	LRI $CR, #0x0001
+	; Observed: still writes to TEST_REG
+	SI @TEST_ADDR, #0xf55f
+	CALL send_regs
+
+	LRI $AC0.L, #0xf66f
+	; Observed: writes to TEST_MEM_2
+	SRS @TEST_ADDR, $AC0.L
+	CALL send_regs
+
+	; At this point, TEST_REG should be f55f, TEST_MEM should be f44f,
+	; and TEST_MEM_2 should be f66f.  Test the behavior of LRS.
+	; Changes to prod.l are for display only.
+	LRI $CR, #0x00ff
+	LRI $prod.l, #0xf55f
+	LRS $AC0.L, @TEST_ADDR
+	CALL send_regs
+
+	LRI $CR, #0x0000
+	LRI $prod.l, #0xf44f
+	LRS $AC0.L, @TEST_ADDR
+	CALL send_regs
+
+	LRI $CR, #0x0001
+	LRI $prod.l, #0xf66f
+	LRS $AC0.L, @TEST_ADDR
+	CALL send_regs
+
+; We're done, DO NOT DELETE THIS LINE
+	JMP end_of_test
+
+send_regs:
+	; For display purposes only
+	LRI $prod.m1, #TEST_REG
+	LRI $prod.h,  #TEST_MEM
+	LRI $prod.m2, #TEST_MEM_2
+	; Actual registers
+	LR $AC1.L, @TEST_REG
+	LR $AC0.M, @TEST_MEM
+	LR $AC1.M, @TEST_MEM_2
+	CALL send_back
+	RET

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}