cpu/m68000: Stub out the Coprocesor Interface Registers found on '010-'030 so that Mac ROMs can detect if an FPU is present. [R. Belmont]

src/devices/cpu/m68000/m68kcpu.h

@@ -656,6 +656,16 @@ inline u32 m68ki_read_8_fc(u32 address, u32 fc)
 	m_mmu_tmp_fc = fc;
 	m_mmu_tmp_rw = 1;
 	m_mmu_tmp_sz = M68K_SZ_BYTE;
+	// Check for reading the FPU's CIRs if this is an '020 or '030.
+	// In CPU space (FC 7), addresses 0x0002xxxx are coprocessor interface registers.
+	// Bits 15-13 are the coprocessor ID, and bits 0-4 are the register select.
+	if ((fc == 7) && CPU_TYPE_IS_020_PLUS() && !CPU_TYPE_IS_040_PLUS())
+	{
+		if ((address & 0xffffeff0) == 0x00022000)
+		{
+			return m6888x_read_cir(address);
+		}
+	}
 	return m_read8(address);
 }
 inline u32 m68ki_read_16_fc(u32 address, u32 fc)
@@ -667,6 +677,13 @@ inline u32 m68ki_read_16_fc(u32 address, u32 fc)
 	m_mmu_tmp_fc = fc;
 	m_mmu_tmp_rw = 1;
 	m_mmu_tmp_sz = M68K_SZ_WORD;
+	if ((fc == 7) && CPU_TYPE_IS_020_PLUS() && !CPU_TYPE_IS_040_PLUS())
+	{
+		if ((address & 0xffffeff0) == 0x00022000)
+		{
+			return m6888x_read_cir(address);
+		}
+	}
 	return m_read16(address);
 }
 inline u32 m68ki_read_32_fc(u32 address, u32 fc)
@@ -678,6 +695,13 @@ inline u32 m68ki_read_32_fc(u32 address, u32 fc)
 	m_mmu_tmp_fc = fc;
 	m_mmu_tmp_rw = 1;
 	m_mmu_tmp_sz = M68K_SZ_LONG;
+	if ((fc == 7) && CPU_TYPE_IS_020_PLUS() && !CPU_TYPE_IS_040_PLUS())
+	{
+		if ((address & 0xffffeff0) == 0x00022000)
+		{
+			return m6888x_read_cir(address);
+		}
+	}
 	return m_read32(address);
 }
 
@@ -686,6 +710,14 @@ inline void m68ki_write_8_fc(u32 address, u32 fc, u32 value)
 	m_mmu_tmp_fc = fc;
 	m_mmu_tmp_rw = 0;
 	m_mmu_tmp_sz = M68K_SZ_BYTE;
+	if ((fc == 7) && CPU_TYPE_IS_020_PLUS() && !CPU_TYPE_IS_040_PLUS())
+	{
+		if ((address & 0xffffeff0) == 0x00022000)
+		{
+			m6888x_write_cir(address, value);
+			return;
+		}
+	}
 	m_write8(address, value);
 }
 inline void m68ki_write_16_fc(u32 address, u32 fc, u32 value)
@@ -697,6 +729,14 @@ inline void m68ki_write_16_fc(u32 address, u32 fc, u32 value)
 	m_mmu_tmp_fc = fc;
 	m_mmu_tmp_rw = 0;
 	m_mmu_tmp_sz = M68K_SZ_WORD;
+	if ((fc == 7) && CPU_TYPE_IS_020_PLUS() && !CPU_TYPE_IS_040_PLUS())
+	{
+		if ((address & 0xffffeff0) == 0x00022000)
+		{
+			m6888x_write_cir(address, value);
+			return;
+		}
+	}
 	m_write16(address, value);
 }
 inline void m68ki_write_32_fc(u32 address, u32 fc, u32 value)
@@ -708,6 +748,14 @@ inline void m68ki_write_32_fc(u32 address, u32 fc, u32 value)
 	m_mmu_tmp_fc = fc;
 	m_mmu_tmp_rw = 0;
 	m_mmu_tmp_sz = M68K_SZ_LONG;
+	if ((fc == 7) && CPU_TYPE_IS_020_PLUS() && !CPU_TYPE_IS_040_PLUS())
+	{
+		if ((address & 0xffffeff0) == 0x00022000)
+		{
+			m6888x_write_cir(address, value);
+			return;
+		}
+	}
 	m_write32(address, value);
 }
 

src/devices/cpu/m68000/m68kfpu.cpp

@@ -2548,3 +2548,44 @@ void m68000_musashi_device::m68881_ftrap()
 		}
 	}
 }
+
+// Read the FPU's Coprocessor Interface Registers (CIRs).
+// References: MC68881/68882 Coprocessor User's Manual 1st Edition,
+// pages 7-1 to 7-8 and M68030 User's Manual 3rd Edition page 7-69.
+u32 m68000_musashi_device::m6888x_read_cir(offs_t offset)
+{
+	// If no FPU is present, reading any CIRs causes a bus error.
+	// Pre-1992 Macintosh ROMs use this method to detect the presence
+	// of an FPU.  1992 and later ROMs just execute FNOP and check for
+	// an F-line trap, because this mechanism does not exist on the 68040.
+	if (!m_has_fpu)
+	{
+		m68k_cause_bus_error();
+	}
+
+	// TODO: actually try to return meaningful values?
+	// offset   function
+	// 0x00     Response            read-only       16 bit (value in D31-D16)
+	// 0x02     Control             write-only      16
+	// 0x04     Save                read            16
+	// 0x06     Restore             read/write      16
+	// 0x08     Operation Word      read/write      16
+	// 0x0a     Command             write-only      16
+	// 0x0c     (reserved)          N/A             16
+	// 0x0e     Condition           write-only      16
+	// 0x10     Operand             read/write      32 bit
+	// 0x14     Register Select     read-only       16
+	// 0x18     Instruction Address write-only      32
+	// 0x1c     Operand Address     read/write      32
+	return 0;
+}
+
+void m68000_musashi_device::m6888x_write_cir(offs_t offset, u32 data)
+{
+	if (!m_has_fpu)
+	{
+		m68k_cause_bus_error();
+	}
+
+	// TODO: actually do something with these values?
+}

src/devices/cpu/m68000/m68kmusashi.h

@@ -378,6 +378,8 @@ protected:
 	void m68040_do_frestore(u32 addr, int reg);
 	void m68040_fpu_op1();
 	void m68881_ftrap();
+	u32 m6888x_read_cir(offs_t offset);
+	void m6888x_write_cir(offs_t offset, u32 data);
 };
 
 #endif // MAME_CPU_M68000_M68KMUSASHI_H