pofo.cpp: Atari Portfolio fixes and improvements. (#8191)

* Fixed RAM expander reads.
* Implemented magic port 0x61.
* Fixed external drive B: detection.
* Improved control register 0x8051 emulation.

src/devices/bus/pofo/hpc104.cpp

@@ -169,7 +169,7 @@ uint8_t pofo_hpc104_device::nrdi_r(offs_t offset, uint8_t data, bool iom, bool b
 		{
 			if (offset >= 0x1f000 && offset < 0x5f000)
 			{
-				data = m_nvram[offset - 0x1f000] = data;
+				data = m_nvram[offset - 0x1f000];
 			}
 		}
 	}

src/mame/drivers/pofo.cpp

@@ -113,10 +113,10 @@ private:
 
 	enum
 	{
-		ROM_APP,
+		ROM_APP = 0b000, // 0
-		CCM_A,
+		CCM_A   = 0b011, // 3
-		CCM_B,
+		CCM_B   = 0b111, // 7
-		ROM_EXT
+		ROM_EXT = 0b010, // 2
 	};
 
 	uint8_t mem_r(offs_t offset);
@@ -233,9 +233,17 @@ WRITE_LINE_MEMBER( portfolio_state::keyboard_int_w )
 
 uint8_t portfolio_state::irq_status_r()
 {
-	return m_ip;
+	uint8_t data = m_ip;
-}
+	/*
+		The BIOS interrupt 11h (Equipment list) reports that the second floppy drive (B:) is
+		installed if the 3rd bit is set (which is also the external interrupt line).
+		It is not clear if the ~NMD1 line is OR or XORed or muxed with the interrupt line,
+		but this way seems to work.
+	*/
+	data |= !m_exp->nmd1_r() << 3;
 
+	return data;
+}
 
 //-------------------------------------------------
 //  irq_mask_w - interrupt enable mask
@@ -361,10 +369,10 @@ uint8_t portfolio_state::battery_r()
 
 	    bit     signal      description
 
-	    0       ?           1=boots from B:
+	    0       ?           bit 0 from bus select (m_rom_b)
-	    1       ?           1=boots from external ROM
+	    1       ?
-	    2       ?           1=boots from B:
+	    2       ?           bit 2 from bus select (m_rom_b)
-	    3       ?           1=boots from ???
+	    3       ?
 	    4       ?
 	    5       PDET        1=peripheral connected
 	    6       LOWB        0=battery low
@@ -374,6 +382,14 @@ uint8_t portfolio_state::battery_r()
 
 	uint8_t data = 0;
 
+	/*
+		Partially stores what has been written into this port.
+		Used by interrupt 61h service 24h (Get ROM/CCM state).
+		Setting bit 1 here causes the BIOS to permanently wedge the external ROM
+		select on, so mask it out as a workaround.
+	*/
+	data |= (m_rom_b & 0b101);
+
 	// peripheral detect
 	data |= m_exp->pdet_r() << 5;
 
@@ -407,13 +423,7 @@ void portfolio_state::select_w(uint8_t data)
 
 	if (LOG) logerror("%s %s SELECT %02x\n", machine().time().as_string(), machine().describe_context(), data);
 
-	switch (data & 0x0f)
+	m_rom_b = data & 0x0f;
-	{
-	case 3: m_rom_b = CCM_A; break;
-	case 7: m_rom_b = CCM_B; break;
-	case 0: m_rom_b = ROM_APP; break;
-	case 2: m_rom_b = ROM_EXT; break;
-	}
 }
 
 
@@ -530,6 +540,10 @@ uint8_t portfolio_state::mem_r(offs_t offset)
 		case ROM_EXT:
 			// TODO
 			break;
+
+		default:
+			logerror("%s %s Invalid bus read %05x\n", machine().time().as_string(), machine().describe_context(), offset & 0x1ffff);
+			break;
 		}
 	}
 	else if (offset >= 0xe0000)
@@ -574,6 +588,14 @@ void portfolio_state::mem_w(offs_t offset, uint8_t data)
 		case CCM_B:
 			ncc1 = 0;
 			break;
+
+		case ROM_EXT:
+		case ROM_APP:
+			break;
+
+		default:
+			logerror("%s %s Invalid bus write %05x\n", machine().time().as_string(), machine().describe_context(), offset & 0x1ffff);
+			break;
 		}
 	}
 
@@ -632,6 +654,11 @@ uint8_t portfolio_state::io_r(offs_t offset)
 			break;
 		}
 	}
+	else if (offset == 0x61)
+	{
+		// Magic port to detect the Pofo
+		data = 0x61;
+	}
 
 	data = m_exp->nrdi_r(offset, data, iom, bcom, ncc1);