Merge pull request #10692 from Pokechu22/dsp-manual-set40-and-write-backlog

docs/DSP: Add sections on 16-bit and 40-bit modes and on main and extended opcode writing to the same register

Source/Core/Core/DSP/Interpreter/DSPIntArithmetic.cpp

@@ -45,7 +45,7 @@ void Interpreter::clrl(const UDSPInstruction opc)
 //----
 
 // ANDCF $acD.m, #I
-// 0000 001r 1100 0000
+// 0000 001d 1100 0000
 // iiii iiii iiii iiii
 // Set logic zero (LZ) flag in status register $sr if result of logic AND of
 // accumulator mid part $acD.m with immediate value I is equal to I.
@@ -61,7 +61,7 @@ void Interpreter::andcf(const UDSPInstruction opc)
 }
 
 // ANDF $acD.m, #I
-// 0000 001r 1010 0000
+// 0000 001d 1010 0000
 // iiii iiii iiii iiii
 // Set logic zero (LZ) flag in status register $sr if result of logical AND
 // operation of accumulator mid part $acD.m with immediate value I is equal
@@ -81,7 +81,7 @@ void Interpreter::andf(const UDSPInstruction opc)
 
 // TST
 // 1011 r001 xxxx xxxx
-// Test accumulator %acR.
+// Test accumulator $acR.
 //
 // flags out: --xx xx00
 void Interpreter::tst(const UDSPInstruction opc)
@@ -143,11 +143,12 @@ void Interpreter::cmpaxh(const UDSPInstruction opc)
   ZeroWriteBackLog();
 }
 
-// CMPI $amD, #I
-// 0000 001r 1000 0000
+// CMPI $acD, #I
+// 0000 001d 1000 0000
 // iiii iiii iiii iiii
-// Compares mid accumulator $acD.hm ($amD) with sign extended immediate value I.
-// Although flags are being set regarding whole accumulator register.
+// Compares accumulator with immediate. Comparison is executed
+// by subtracting the immediate (16-bit sign extended) from mid accumulator
+// $acD.hm and computing flags based on whole accumulator $acD.
 //
 // flags out: x-xx xxxx
 void Interpreter::cmpi(const UDSPInstruction opc)
@@ -166,8 +167,8 @@ void Interpreter::cmpi(const UDSPInstruction opc)
 
 // CMPIS $acD, #I
 // 0000 011d iiii iiii
-// Compares accumulator with short immediate. Comaprison is executed
-// by subtracting short immediate (8bit sign extended) from mid accumulator
+// Compares accumulator with short immediate. Comparison is executed
+// by subtracting the short immediate (8-bit sign extended) from mid accumulator
 // $acD.hm and computing flags based on whole accumulator $acD.
 //
 // flags out: x-xx xxxx
@@ -320,7 +321,7 @@ void Interpreter::notc(const UDSPInstruction opc)
 }
 
 // XORI $acD.m, #I
-// 0000 001r 0010 0000
+// 0000 001d 0010 0000
 // iiii iiii iiii iiii
 // Logic exclusive or (XOR) of accumulator mid part $acD.m with
 // immediate value I.
@@ -337,7 +338,7 @@ void Interpreter::xori(const UDSPInstruction opc)
 }
 
 // ANDI $acD.m, #I
-// 0000 001r 0100 0000
+// 0000 001d 0100 0000
 // iiii iiii iiii iiii
 // Logic AND of accumulator mid part $acD.m with immediate value I.
 //
@@ -354,7 +355,7 @@ void Interpreter::andi(const UDSPInstruction opc)
 }
 
 // ORI $acD.m, #I
-// 0000 001r 0110 0000
+// 0000 001d 0110 0000
 // iiii iiii iiii iiii
 // Logic OR of accumulator mid part $acD.m with immediate value I.
 //
@@ -489,8 +490,8 @@ void Interpreter::addaxl(const UDSPInstruction opc)
   UpdateSR64Add(acc, acx, GetLongAcc(dreg));
 }
 
-// ADDI $amR, #I
-// 0000 001r 0000 0000
+// ADDI $acD, #I
+// 0000 001d 0000 0000
 // iiii iiii iiii iiii
 // Adds immediate (16-bit sign extended) to mid accumulator $acD.hm.
 //

Source/Core/Core/DSP/Interpreter/DSPInterpreter.cpp

@@ -16,8 +16,23 @@
 
 namespace DSP::Interpreter
 {
-// Not needed for game ucodes (it slows down interpreter + easier to compare int VS
-// dspjit64 without it)
+// Correctly handle instructions such as `INC'L $ac0 : $ac0.l, @$ar0` (encoded as 0x7660) where both
+// the main opcode and the extension opcode modify the same register. See the "Extended opcodes"
+// section in the manual for more details.  No official uCode writes to the same register twice like
+// this, so we don't emulate it by default (and also don't support it in the recompiler).
+//
+// Dolphin only supports this behavior in the interpreter when PRECISE_BACKLOG is defined.
+// In ExecuteInstruction, if an extended opcode is in use, the extended opcode's behavior is
+// executed first, followed by the main opcode's behavior. The extended opcode does not directly
+// write to registers, but instead records the writes into a backlog (WriteToBackLog). The main
+// opcode calls ZeroWriteBackLog after it is done reading the register values; this directly
+// writes zero to all registers that have pending writes in the backlog. The main opcode then is
+// free to write directly to registers it changes. Afterwards, ApplyWriteBackLog bitwise-ors the
+// value of the register and the value in the backlog; if the main opcode didn't write to the
+// register then ZeroWriteBackLog means that the pending value is being or'd with zero, so it's
+// used without changes. When PRECISE_BACKLOG is not defined, ZeroWriteBackLog does nothing and
+// ApplyWriteBackLog overwrites the register value with the value from the backlog (so writes from
+// extended opcodes "win" over the main opcode).
 //#define PRECISE_BACKLOG
 
 Interpreter::Interpreter(DSPCore& dsp) : m_dsp_core{dsp}
@@ -809,7 +824,7 @@ void Interpreter::ConditionalExtendAccum(int reg)
 void Interpreter::ApplyWriteBackLog()
 {
   // Always make sure to have an extra entry at the end w/ -1 to avoid
-  // infinitive loops
+  // infinite loops
   for (int i = 0; m_write_back_log_idx[i] != -1; i++)
   {
     u16 value = m_write_back_log[i];
@@ -823,6 +838,11 @@ void Interpreter::ApplyWriteBackLog()
   }
 }
 
+// The ext ops are calculated in parallel with the actual op. That means that
+// both the main op and the ext op see the same register state as input. The
+// output is simple as long as the main and ext ops don't change the same
+// register. If they do the output is the bitwise OR of the result of both the
+// main and ext ops.
 void Interpreter::WriteToBackLog(int i, int idx, u16 value)
 {
   m_write_back_log[i] = value;
@@ -840,7 +860,7 @@ void Interpreter::ZeroWriteBackLog()
 {
 #ifdef PRECISE_BACKLOG
   // always make sure to have an extra entry at the end w/ -1 to avoid
-  // infinitive loops
+  // infinite loops
   for (int i = 0; m_write_back_log_idx[i] != -1; i++)
   {
     OpWriteRegister(m_write_back_log_idx[i], 0);

Source/Core/Core/DSP/Interpreter/DSPInterpreter.h

@@ -235,11 +235,6 @@ private:
 
   void ConditionalExtendAccum(int reg);
 
-  // The ext ops are calculated in parallel with the actual op. That means that
-  // both the main op and the ext op see the same register state as input. The
-  // output is simple as long as the main and ext ops don't change the same
-  // register. If they do the output is the bitwise OR of the result of both the
-  // main and ext ops.
   void WriteToBackLog(int i, int idx, u16 value);
   void ZeroWriteBackLog();
   void ZeroWriteBackLogPreserveAcc(u8 acc);

Source/Core/Core/DSP/Jit/x64/DSPJitArithmetic.cpp

@@ -53,7 +53,7 @@ void DSPEmitter::clrl(const UDSPInstruction opc)
 //----
 
 // ANDCF $acD.m, #I
-// 0000 001r 1100 0000
+// 0000 001d 1100 0000
 // iiii iiii iiii iiii
 // Set logic zero (LZ) flag in status register $sr if result of logic AND of
 // accumulator mid part $acD.m with immediate value I is equal to I.
@@ -88,7 +88,7 @@ void DSPEmitter::andcf(const UDSPInstruction opc)
 }
 
 // ANDF $acD.m, #I
-// 0000 001r 1010 0000
+// 0000 001d 1010 0000
 // iiii iiii iiii iiii
 // Set logic zero (LZ) flag in status register $sr if result of logical AND
 // operation of accumulator mid part $acD.m with immediate value I is equal
@@ -126,7 +126,7 @@ void DSPEmitter::andf(const UDSPInstruction opc)
 
 // TST
 // 1011 r001 xxxx xxxx
-// Test accumulator %acR.
+// Test accumulator $acR.
 //
 // flags out: --xx xx00
 void DSPEmitter::tst(const UDSPInstruction opc)
@@ -220,11 +220,12 @@ void DSPEmitter::cmpaxh(const UDSPInstruction opc)
   }
 }
 
-// CMPI $amD, #I
-// 0000 001r 1000 0000
+// CMPI $acD, #I
+// 0000 001d 1000 0000
 // iiii iiii iiii iiii
-// Compares mid accumulator $acD.hm ($amD) with sign extended immediate value I.
-// Although flags are being set regarding whole accumulator register.
+// Compares accumulator with immediate. Comparison is executed
+// by subtracting the immediate (16-bit sign extended) from mid accumulator
+// $acD.hm and computing flags based on whole accumulator $acD.
 //
 // flags out: x-xx xxxx
 void DSPEmitter::cmpi(const UDSPInstruction opc)
@@ -257,7 +258,7 @@ void DSPEmitter::cmpi(const UDSPInstruction opc)
 // CMPIS $acD, #I
 // 0000 011d iiii iiii
 // Compares accumulator with short immediate. Comparison is executed
-// by subtracting short immediate (8bit sign extended) from mid accumulator
+// by subtracting the short immediate (8-bit sign extended) from mid accumulator
 // $acD.hm and computing flags based on whole accumulator $acD.
 //
 // flags out: x-xx xxxx
@@ -472,7 +473,7 @@ void DSPEmitter::notc(const UDSPInstruction opc)
 }
 
 // XORI $acD.m, #I
-// 0000 001r 0010 0000
+// 0000 001d 0010 0000
 // iiii iiii iiii iiii
 // Logic exclusive or (XOR) of accumulator mid part $acD.m with
 // immediate value I.
@@ -498,7 +499,7 @@ void DSPEmitter::xori(const UDSPInstruction opc)
 }
 
 // ANDI $acD.m, #I
-// 0000 001r 0100 0000
+// 0000 001d 0100 0000
 // iiii iiii iiii iiii
 // Logic AND of accumulator mid part $acD.m with immediate value I.
 //
@@ -523,7 +524,7 @@ void DSPEmitter::andi(const UDSPInstruction opc)
 }
 
 // ORI $acD.m, #I
-// 0000 001r 0110 0000
+// 0000 001d 0110 0000
 // iiii iiii iiii iiii
 // Logic OR of accumulator mid part $acD.m with immediate value I.
 //
@@ -706,8 +707,8 @@ void DSPEmitter::addaxl(const UDSPInstruction opc)
   }
 }
 
-// ADDI $amR, #I
-// 0000 001r 0000 0000
+// ADDI $acD, #I
+// 0000 001d 0000 0000
 // iiii iiii iiii iiii
 // Adds immediate (16-bit sign extended) to mid accumulator $acD.hm.
 //