Bus: Calculation of memory timings for external devices

src/core/bus.cpp

@@ -51,14 +51,15 @@ void Bus::Reset()
   m_ram.fill(static_cast<u8>(0));
   m_MEMCTRL.exp1_base = 0x1F000000;
   m_MEMCTRL.exp2_base = 0x1F802000;
-  m_MEMCTRL.exp1_delay_size = 0x0013243F;
+  m_MEMCTRL.exp1_delay_size.bits = 0x0013243F;
-  m_MEMCTRL.exp3_delay_size = 0x00003022;
+  m_MEMCTRL.exp3_delay_size.bits = 0x00003022;
-  m_MEMCTRL.bios_delay_size = 0x0013243F;
+  m_MEMCTRL.bios_delay_size.bits = 0x0013243F;
-  m_MEMCTRL.spu_delay_size = 0x200931E1;
+  m_MEMCTRL.spu_delay_size.bits = 0x200931E1;
-  m_MEMCTRL.cdrom_delay_size = 0x00020843;
+  m_MEMCTRL.cdrom_delay_size.bits = 0x00020843;
-  m_MEMCTRL.exp2_delay_size = 0x00070777;
+  m_MEMCTRL.exp2_delay_size.bits = 0x00070777;
-  m_MEMCTRL.common_delay_size = 0x00031125;
+  m_MEMCTRL.common_delay.bits = 0x00031125;
   m_ram_size_reg = UINT32_C(0x00000B88);
+  RecalculateMemoryTimings();
 }
 
 bool Bus::DoState(StateWrapper& sw)
@@ -167,6 +168,61 @@ bool Bus::LoadBIOS()
   return true;
 }
 
+std::tuple<TickCount, TickCount, TickCount> Bus::CalculateMemoryTiming(MEMDELAY mem_delay, COMDELAY common_delay)
+{
+  // from nocash spec
+  s32 first = 0, seq = 0, min = 0;
+  if (mem_delay.use_com0_time)
+  {
+    first += s32(common_delay.com0) - 1;
+    seq += s32(common_delay.com0) - 1;
+  }
+  if (mem_delay.use_com2_time)
+  {
+    first += s32(common_delay.com2);
+    seq += s32(common_delay.com2);
+  }
+  if (mem_delay.use_com3_time)
+  {
+    min = s32(common_delay.com3);
+  }
+  if (first < 6)
+    first++;
+
+  first = first + s32(mem_delay.access_time) + 2;
+  seq = seq + s32(mem_delay.access_time) + 2;
+
+  if (first < (min + 6))
+    first = min + 6;
+  if (seq < (min + 2))
+    seq = min + 2;
+
+  const TickCount byte_access_time = first;
+  const TickCount halfword_access_time = mem_delay.data_bus_16bit ? first : (first + seq);
+  const TickCount word_access_time = mem_delay.data_bus_16bit ? (first + seq) : (first + seq + seq + seq);
+  return std::tie(byte_access_time, halfword_access_time, word_access_time);
+}
+
+void Bus::RecalculateMemoryTimings()
+{
+  std::tie(m_bios_access_time[0], m_bios_access_time[1], m_bios_access_time[2]) =
+    CalculateMemoryTiming(m_MEMCTRL.bios_delay_size, m_MEMCTRL.common_delay);
+  std::tie(m_cdrom_access_time[0], m_cdrom_access_time[1], m_cdrom_access_time[2]) =
+    CalculateMemoryTiming(m_MEMCTRL.cdrom_delay_size, m_MEMCTRL.common_delay);
+  std::tie(m_spu_access_time[0], m_spu_access_time[1], m_spu_access_time[2]) =
+    CalculateMemoryTiming(m_MEMCTRL.spu_delay_size, m_MEMCTRL.common_delay);
+
+  Log_DevPrintf("BIOS Memory Timing: %u bit bus, byte=%d, halfword=%d, word=%d",
+                m_MEMCTRL.bios_delay_size.data_bus_16bit ? 16 : 8, m_bios_access_time[0], m_bios_access_time[1],
+                m_bios_access_time[2]);
+  Log_DevPrintf("CDROM Memory Timing: %u bit bus, byte=%d, halfword=%d, word=%d",
+                m_MEMCTRL.cdrom_delay_size.data_bus_16bit ? 16 : 8, m_cdrom_access_time[0], m_cdrom_access_time[1],
+                m_cdrom_access_time[2]);
+  Log_DevPrintf("SPU Memory Timing: %u bit bus, byte=%d, halfword=%d, word=%d",
+                m_MEMCTRL.spu_delay_size.data_bus_16bit ? 16 : 8, m_spu_access_time[0], m_spu_access_time[1],
+                m_spu_access_time[2]);
+}
+
 bool Bus::DoInvalidAccess(MemoryAccessType type, MemoryAccessSize size, PhysicalMemoryAddress address, u32& value)
 {
   SmallString str;
@@ -292,7 +348,16 @@ bool Bus::DoReadMemoryControl(MemoryAccessSize size, u32 offset, u32& value)
 bool Bus::DoWriteMemoryControl(MemoryAccessSize size, u32 offset, u32 value)
 {
   FixupUnalignedWordAccessW32(offset, value);
-  m_MEMCTRL.regs[offset / 4] = value;
+
+  const u32 index = offset / 4;
+  const u32 write_mask = (index == 8) ? COMDELAY::WRITE_MASK : MEMDELAY::WRITE_MASK;
+  const u32 new_value = (m_MEMCTRL.regs[index] & ~write_mask) | (value & write_mask);
+  if (m_MEMCTRL.regs[index] != new_value)
+  {
+    m_MEMCTRL.regs[index] = new_value;
+    RecalculateMemoryTimings();
+  }
+
   return true;
 }
 

src/core/bus.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "YBaseLib/String.h"
+#include "common/bitfield.h"
 #include "types.h"
 #include <array>
 
@@ -95,6 +96,34 @@ private:
     MEMCTRL_REG_COUNT = 9
   };
 
+  union MEMDELAY
+  {
+    u32 bits;
+
+    BitField<u32, u8, 4, 4> access_time; // cycles
+    BitField<u32, bool, 8, 1> use_com0_time;
+    BitField<u32, bool, 9, 1> use_com1_time;
+    BitField<u32, bool, 10, 1> use_com2_time;
+    BitField<u32, bool, 11, 1> use_com3_time;
+    BitField<u32, bool, 12, 1> data_bus_16bit;
+    BitField<u32, u8, 16, 5> memory_window_size;
+
+    static constexpr u32 WRITE_MASK = 0b10101111'00011111'11111111'11111111;
+  };
+
+  union COMDELAY
+  {
+    u32 bits;
+
+    BitField<u32, u8, 0, 4> com0;
+    BitField<u32, u8, 4, 4> com1;
+    BitField<u32, u8, 8, 4> com2;
+    BitField<u32, u8, 12, 4> com3;
+    BitField<u32, u8, 16, 2> comunk;
+
+    static constexpr u32 WRITE_MASK = 0b00000000'00000011'11111111'11111111;
+  };
+
   union MEMCTRL
   {
     u32 regs[MEMCTRL_REG_COUNT];
@@ -103,18 +132,21 @@ private:
     {
       u32 exp1_base;
       u32 exp2_base;
-      u32 exp1_delay_size;
+      MEMDELAY exp1_delay_size;
-      u32 exp3_delay_size;
+      MEMDELAY exp3_delay_size;
-      u32 bios_delay_size;
+      MEMDELAY bios_delay_size;
-      u32 spu_delay_size;
+      MEMDELAY spu_delay_size;
-      u32 cdrom_delay_size;
+      MEMDELAY cdrom_delay_size;
-      u32 exp2_delay_size;
+      MEMDELAY exp2_delay_size;
-      u32 common_delay_size;
+      COMDELAY common_delay;
     };
   };
 
   bool LoadBIOS();
 
+  static std::tuple<TickCount, TickCount, TickCount> CalculateMemoryTiming(MEMDELAY mem_delay, COMDELAY common_delay);
+  void RecalculateMemoryTimings();
+
   template<MemoryAccessType type, MemoryAccessSize size>
   bool DoRAMAccess(u32 offset, u32& value);
 
@@ -172,6 +204,10 @@ private:
   SPU* m_spu = nullptr;
   MDEC* m_mdec = nullptr;
 
+  std::array<TickCount, 3> m_bios_access_time = {};
+  std::array<TickCount, 3> m_cdrom_access_time = {};
+  std::array<TickCount, 3> m_spu_access_time = {};
+
   std::array<u8, 2097152> m_ram{}; // 2MB RAM
   std::array<u8, 524288> m_bios{}; // 512K BIOS ROM
   std::vector<u8> m_exp1_rom;